In this talk, we present the development of massive MIMO antenna technologies for the 5G and associated challenges. The overall system performance and antenna design-choice in terms of spectrum and channel propagation properties are discussed. In particular, we further present the novel massive MIMO antenna design to achieve higher capacity with same antenna aperture size and the field trial results. We also discuss the directions for the evolution of massive MIMO antenna for 6G.

Metamaterials are artificial materials with electromagnetic properties that go well beyond what offered by nature, providing unprecedented opportunities to tailor and enhance the interaction between waves and matter. In this talk, I discuss our recent research activity in this area of technology, with special emphasis on the opportunities offered by metamaterials for wireless, radio-frequency and mm-wave applications. In particular, I will discuss how suitably tailored meta-atoms and careful arrangements of them can open exciting venues to manipulate and control electromagnetic waves in unprecedented ways. I will discuss our recent work on metamaterials for scattering suppression applied to antenna technologies, metasurfaces to control wave propagation and radiation in extreme ways, circulators and isolators that do not require a magnetic bias, and active metasurfaces for next-generation wireless systems. Physical insights into the exotic phenomena underlying these device functionalities, new technologies based on these concepts, and their practical impact will be discussed during the talk.

Antennas are the ears and eyes of the satellites and allows them to communicate and deliver the information to the users. There is an historical trend to improve the efficiency of satellite antennas in all aspects. Larger sizes, more power handling, lower passive intermodulation, more flexibility and adaptability are required and always taking into account the special needs of space applications. Satellite antennas need to keep all performances in a very harsh environment including extreme temperatures, high radiation and launch loads, all with a minimum mass and compact enough to be fitted into the launchers fairing. Satellite antennas have large differences depending on the orbit of the application, from Low Earth Orbit (LEO) to interplanetary missions. A look around different applications and orbits will be presented showing the latest trends in the different solutions that are used.

A low profile three element half cylindrical dielectric resonator antenna with Multiple Input Multiple Output (MIMO) application is demonstrated. Antenna element and the feeding scheme is arranged orthogonally in space to minimize mutual coupling between antenna elements. This antenna arrangement offers space diversity with radiation pattern diversity. Proposed antenna is fabricated and experimentally verified. Rogers TMM10 (εr = 11.2), a low loss dielectric material is used to fabricate the antenna. Antenna offers a close agreement between simulated and measured results. Proposed antenna element DRA-1 offers 9 - 11.1 GHz, DRA -2 offers 9.2 - 10.6 GHz and DRA -3 offers 8.7 - 11.6 GHz frequency band of operation respectively. It offers 8.3 dBi peak gain at 10 GHz frequency and more than 80% radiation efficiency over the operating frequency range.

The Degrees of Freedom (DoF) of the radiated field are linked to the MIMO antenna design, since the DoF represent an upperbound for the effective number of degrees of freedom of a MIMO channel and also they represent a limit to the number of users in multi-user MIMO communications. The DoF are normally defined at a certain distance from a minimum surface enclosing the sources, so that the reactive field is negligible. This paper suggests an extension of the DoF concept to include a dependency on the frequency bandwidth, and a process for its calculation. This is done by introducing the ratio between the reactive energy stored in the vicinity of the radiating surface and the radiated power as a measure of the source frequency bandwidth. The problem is here treated analytically for a spherical source region by using spherical wave harmonics.

This paper presents a sequentially rotated quad-element, triple-band MIMO antenna, operating in the sub 6 GHz frequency bands. The individual antenna elements have three resonant frequencies at 3.74, 4.87, and 5.87 GHz, with a frequency separation ratio of 1:1.3:1.56. The three frequency bands are achieved using an inverted F shaped structure connected to a rectangular microstrip patch, with a slot along the width of the patch. The antenna elements have an edge-to-edge gap of 1.9 mm. The achieved isolation between the antenna elements is more than 20 dB and 15 dB respectively at adjacent and diagonal element over all three frequency bands. The proposed quad-element antenna provides a gain of 6.73, 6.06, and 5.83 dBi and efficiency of 84.6%, 80%, and 88% at 3.74, 4.87, and 5.87 GHz, respectively. The ECC, TARC and CCL values are less than 0.05, -10 dB, and 0.5 bits/s/Hz respectively over all three bands.

A planar multi-beam microstrip antenna (MSA) array with low SLL is presented in this paper. The beam forming network is integrated with a 11x5 MSA array to form a low profile multi-beam antenna array design. Each linear array is fed by multiple meandered feed lines, which provide desired phase shift for beam-forming. The multi-beam antenna elements are tapered with binomial distribution to suppress SLL below -20dB in E-Plane. The array generates five beams and the individual gain of the beams are 14, 15, 14.5, 14.4, 12 dBi at 3.42 GHz. The |S11| less than equal to -10dB impedance bandwidth of all the ports is from 3.3-3.5 GHz and the isolation between consecutive ports is better than 20 dB for most of the bandwidth.

This paper presents SICL fed wideband MIMO antenna array for 5G endfire applications. The radiating element in the array is a modified dipole antenna formed by titled at ±45degree to avoid overlapping between successive element in the array configuration. One arm is placed on the top while the other arm is placed on the bottom substrate and are respectively fed by top and middle plate (using a feeding via) of SICL line. The top-bottom arrangement of the arms of dipole antenna enables further compactness in the dimension of the array. SICL technology adds another advantage by reducing the coupling in the other port when one port is excited thereby high isolation is achieved using SICL. A four element MIMO antenna array for 360degree azimuth coverage is proposed to exhibit a gain of 6 dBi with wide impedance bandwidth of 5.6 GHz and cross-polarization level below 13.6 dB at 28 GHz.

This paper presents some of the last solutions studied to fulfill the flexibility and high capacity demand of complex Very High Throughput and Government Satellites. A description of the concept and two antenna samples have been included.

This paper presents a metal-only reflectarray antenna made of 3D phoenix cells and its fabrication using additive manufacturing. An electric circuit is proposed for analyzing the behavior and capabilities of the considered cell. The agreement between full-wave simulations and the circuit predictions is very satisfactory when varying the cell geometrical parameters on a large range of values. The simulated gain of the designed reflectarray at 20 GHz is 30.3 dBi with an efficiency of 50.33% and a 1 dB-gain bandwidth of 10.75%. The proposed reflectarray is suitable for working in severe environments due to its metal-only characteristics.

This article presents a matrix antenna operating in the L-band and designed for signal jamming applications. The matrix, composed of pixel elements is reduced to 0.31 ∗ λ at 1.2 GHz by filling the cavity with a dielectric. This allows the matrix to achieve a wide bandwidth of 1.21 GHz to 1.6 GHz. The maximum steering angle achieved over the whole band is 70° while maintaining side-lobes levels lower than -9.3 dB and a stable gain.

NISAR (NASA ISRO SAR, National Aeronautics and Space Administration, Indian Space Research Organization, Synthetic Aperture Radar) is an Earth science project currently in its final development phases at NASA Jet Propulsion Laboratory (JPL) and at ISRO. Due for launch in 2023 it will assess how our planet changes over time by measuring differences in the Earth's solid surface due to factors like climate change, movement and melting of glaciers, earthquakes, land-slides, deforestation, agriculture and others. The enabling instrument for this mission is a dual band radar (L-Band and S-Band) that feeds a 12m deployable mesh reflector. Given the extreme accuracy needed to perform these measurements from Low Earth Orbit (LEO) some of the most stringent requirements were pushed onto the antenna subsystem to control phase and gain stability over time. In this paper we describe how environmental requirements affected the antenna design and what techniques were used to meet these requirements.

Autonomous underwater vehicles (AUVs) gain increasing popularity in the underwater domain. They are particularly suitable for carrying out surveys in areas where manned operation is too dangerous or too expensive, examples being deep sea environments or naval mine clearing operations. However, to make full use of their capabilities, a communication link between AUV and its host platform is necessary. This paper proposes a design for an ultra high frequency (UHF) wideband antenna that can be mounted on mid-sized AUVs. The antenna covers the entire naval UHF frequency band from 225MHz to 400MHz with a reflection coefficient lower than -10dB and an omni-directional radiation pattern. Water effects are taken into account in both, simulations and measurements indicating a stable antenna performance.

Demonstration of the electromagnetic hardening properties of a plasma-based electrically small VHF antenna is presented in this paper. It is shown that when illuminated by an electromagnetic pulse, the maximum voltage collected by the antenna grows linearly with the maximum magnitude of the incident electric field, but beyond a certain threshold around 70 kV/m, the maximum voltage collected ceases to grow linearly and seems to saturate around a value of 200 V.

This paper presents three handset antenna array configurations when each array is 1×4, with a capability of multiple steering angles at an operating frequency of 28GHz. The purpose is to maximize the overall achievable directivity to provide quasi-omni-directional coverage to the handset in millimeter wave (mmWave) 5G frequency bands. Generally, radiation fields from a mmWave antenna suffer high and low directivity regions that severely impact the mmWave 5G service quality. The main objective of this paper is to investigate thoroughly and provide a practical yet simple solution to this problem and ensure close to 100% coverage of a mmWave 5G handset antenna. Antenna array design and investigation around a mobile handset are studied in MATLAB, where combined (resultant) radiation patterns have been numerically calculated as a response of different antenna positions. As commonly used, a standard patch antenna is considered as the handset antenna array unit-cell while cardioid radiation pattern of the single antenna is used for analysis. An overall directivity larger than 0 dB is targeted all around the handset. The result shows that more than 95% of the spherical region can be covered with as low as 6 or 7 steering angle states when used with the proposed antenna array architecture and placement. This investigation focuses only on the handset in free space, while the same investigative approach can be extended for other scenarios like handset in the hand, or handset close of the head, etc.

This paper presents substrate integrated waveguide (SIW) phase shifter that can be reconfigured using liquid metal. The phase shifter is developed to be used for antenna applications. This digital phase shifter incorporates a series of holes which can be filled or emptied of liquid metal, enabling us to add or remove via connections dynamically, on-the-fly. We employ a switched line approach to achieve course phase control along with reactive loading to achieve fine steps of phase control. By employing both forms of reconfiguration in unison the proposed phase shifter is able to deliver a phase shift of up to 180° in steps of 10°. The proposed phase shifter operates at 10 GHz and exhibits a measured insertion loss of less than 2.3 dB over its entire operating band.

In this paper, we critically examine the frequency dependent path-loss characteristics and impacts of multiple additional side-lobes in the radiated beams (i.e. scalloping) in an IRS (intelligent reflecting surface) assisted SISO (single-input single-output) communication link. Using Method-of-Moment based MATLAB Antenna Toolbox, we analyze a system of two half-wavelength thin-wire dipoles placed near a planar IRS comprising of circular thin-wire loops. We showcase that, besides the IRS aperture size, the IRS unit-cell dimensions also play a crucial role in shaping the frequency dependent path-loss features. Considering the transmitter and IRS as a unified radiator, we further highlight the importance of properly accounting for multiple additional lobes appearing in the radiating beam due to presence of large reflector, which can cause ripple like variation in the path-loss characteristics. Finally, we demonstrate the significant impact of IRS positioning with respect to the transmit-receive system in altering the frequency dependent pathloss behaviour.

This paper introduces a 3D printed slotted waveguide linear antenna array at 28 GHz. The proposed antenna offers the advantages of low fabrication cost and reduced weight compared to the metallic slotted waveguide antenna array. The proposed design can achieve a high gain, low losses, and simplicity with the fabrication. The proposed antenna geometry suggests an operating bandwidth of 15.8% (26.45 GHz - 31 GHz) suitable to fulfil 5G demands with the high gain performance of 12.0 dBi over the operating bandwidth.

A two directional scanning conformal array that can be used as transmitter for wirelessly powered sensors, is presented. The array consists of two perpendicular threeelement linear arrays that form a cross. Prob-fed square patch antennas form the basic radiating element. The total gain of each array is 9 dBi. Each linear array is conformed around a cylindrical surface and can direct the main beam in three directions; the broadside and two oblique directions that form +/- 37 o angle with the broadside direction. In total, the main beam can be directed in 5 distinct directions. The direction can be selected from a microcontroller that provides the DC biasing voltage to the single pole double through (SPDT) switches which are used for the implementation of a phase shifter. The in-phase or 120 o phase difference signals are produced from the phase shifter that is cascaded with a 4-port power divider, which has one input and three output ports with output power ratios 1:2:1. At any time, only one of the two perpendicular linear arrays can radiate, since the output of the commonly used phase sifter can be directed either to one the other array. Despite the non-symmetric geometry of the phase shifter and the distinct different biasing states of the used SPDT switches, the array remains well matched regardless the selected main beam direction.

Next-generation wireless communication systems are characterized by stringent requirements in terms of data rates, integrability and reconfigurability. The paradigm of metasurfaces offers an exciting platform to address the associated challenges, especially when considering the opportunity to integrate conventional metasurface elements with active, nonlinear and time-varying components suitably tailored and controlled in real-time to respond to changes in the background. These components can tackle large signal-to-noise ratios, nonreciprocal scattering matrices, real-time reconfigurability and broadband responses, beyond the limitations of conventional communication technologies. By leveraging the latest advances in metasurface technologies and connecting them with the recent progress of the wireless communications and systems community, it may be possible to envision disruptive directions for antenna and beamforming technologies beyond 5G systems.

In this paper we propose a novel real-time tracking method of a moving UHF-RFID tag. Two antenna pairs fixed at predefined positions monitor the moving tag collecting phase measurements. Phase differences are calculated for each pair and then mapped to distance-differences of the two antennas from the target tag. The latter corresponds to a hyperbola for each pair of antenna. The intersection of the two hyperbolas denotes the position of the tag. Since solving the system of hyperbolas to find the intersection point is not feasible with standard practices, a neural network is exploited to approximate the solution. Compared to prior art, the proposed method does not require knowledge of the tag's initial position or the trace followed (e.g. conveyor belt). Experiments were conducted by placing a tag on a moving robot capable of performing SLAM (Simultaneous Localization and Mapping) to know the ground truth. The results showed a mean error under 0.5m throughout the experimental campaign.

In this paper, we propose a novel encoding strategy for chipless-RFID systems based on near-field coupling and sequential bit reading, where the bits are read synchronously. The main purpose of this encoding strategy is to increase the data density per unit length (DPL) and surface (DPS) of the tags, as compared to those data densities achievable with a conventional encoding scheme. Such new encoding uses both the rising and falling edges of a clock signal, generated by the motion of the tag over the sensitive part of the reader. Experimental validation is demonstrated by fabricating and reading two 19-bit tags. Such tags consist of two chains of rectangular metallic patches, whereas the sensitive part of the reader is based on a microstrip transmission line loaded with two different and uncoupled complementary split ring resonators (CSRRs).

This paper presents a safety system based on passive UHF-RFID technology to be applied in agricultural and forestry working areas where human workers and remote-control farm machineries operates concurrently. Workers and obstacles are equipped with at least a pair of tags, whereas the machineries carry an on-board RFID reader and an array antenna. An Unscented Kalman Filter, which exploits ranging and Direction of Arrival (DoA) measurements, computes the relative location of worker/obstacle with respect to the machinery. In case of unsafe distance, an alert signal is emitted. This smart system is conceived within the SMARTGRID project, in collaboration with INAIL (Italian National Institute for the prevention of accidents at work).

Automated Guided Vehicles (AGVs) are mobile robots that are capable of navigating with little or no human intervention. AGVs are found in different fields such as measurements, scanning, and automation. In industry, AGVs are used to improve efficiency and productivity. This growing use of AGVs drives the research towards developing and optimizing navigation accuracy. In this paper, a lateral misalignment radiofrequency sensor for navigation of AGV is presented. The navigation principle is based on laying down a path of resonators that guides the vehicle along the required trajectory. The wireless sensor design presented here can detect deviations from the desired path in the range of 10 cm. However, one of the key features of the proposed sensor is its scalability for different ranges and operating frequencies that may be required in different practical scenarios. The sensing concept was verified using electromagnetic simulations, and finally, a navigation control logic is proposed.

Herein we present a compact sensing system based on a surface acoustic wave (SAW) device coupled to a thin flexible antenna for health monitoring. The system operates in the 2.4GHz ISM band. It provides interesting radiation characteristics when tattooed on the human skin and preserves a satisfactory behavior even when it is conformed to the deformations of the human body. In addition, the simulations show that the specific absorption rate (SAR) of this system respects the international standards and regulations for RF exposure, which makes it harmless to the human health.

In this communication, we describe the proof-of-concept for an interconnect-free DRA-SAW high temperature sensing system. The basic concept is the following: a SAW sensor is integrated within the same layer with a DRA antenna's circular slot feed. The DRA ceramic radiator can also serve as package. A 2.48GHz ISM low temperature demonstrator associating a FR-4 substrate and a commercial SAW resonator was simulated and fabricated. Simulations predict a very good impedance matching, 4.7dB gain and a HPBW of 100° in both E and H planes, an attractive feature for practical sensing applications. Sensing measurements were carried out for the first time with heating between 30°C and 100°C. These initial results pave the way for a fully integrated AlN/Sapphire high temperature SAW-DRA sensing system.

In this paper we design and implement a mobile handheld human operated device used to guide the user towards the desired RFID target and provide estimations of the distance and the angle from the user to the target. The main components of the device are a UHF RFID reader operating with one antenna, and an IMU used to measure rotation angles. The user is instructed by the device to perform one of three different actions: SCAN, TURN and MOVE. During these actions phase of arrival and rotation angle data are collected by the RFID reader and the IMU respectively. A particle filter algorithm leverages the collected data to estimate the distance and angle of the user, with respect to the user's current pose. Experimental results show a mean angle estimation error of 4 degrees, and distance estimation error less than 0.5m when the user approaches the target.

An indoor global robot localization problem is considered, where the robot is a differential drive kinematics vehicle. It is equipped with an RFID reader which measures phase shift in the RFID signal back-scattered by a set of RFID passive tags, located on the ceiling of the environment in a known position. The main contribution is the introduction of a special kind of tag, including three antennas close one each other (TriLateration Tag), allowing to obtain an estimate of the robot pose even if only one of these tags is detected. An Extended Kalman Filter is used to fuse odometry readings (encoder steps on robot wheels) with phase measurements obtaining a pose estimate which significantly improves results obtained when using standard one-antenna tags deployed with the same density. Simulation results show the effectiveness of the approach, which is particularly suited for large warehouses where RFID tags cannot be deployed too densely.

In recent years, automatic RFID inventory systems at the UHF band are becoming largely diffused. Therefore, the need to study their effectiveness in terms of inventory accuracy is raising. In this paper, we present a performance assessment analysis of a UHF-RFID robotic inventory system in a real indoor industrial environment. The experimental analysis is conducted at the facilities of Aircraft Cabin Modification - ACM Aerospace GmbH, Memmingen, Germany. In particular, the choice of antenna radiation pattern, distance from the metallic shelving, robot speed, and RFID reader inventory configuration had turned out to be relevant in order to maximize the inventory accuracy. With a proper parameter configuration, a 100% inventory accuracy can be achieved in the company warehouse with high-density tag deployment, by highlighting the robustness of the proposed robot-based RFID inventory system to multipath effect and electromagnetic coupling among tags.

RFID epidermal electronics recently gave us the possibility to connect our body to the external world and gather information about our health and state directly from the skin. To increase the acceptance of the monitoring platforms and overcome the limitations of current technology, i.e. the need of a dedicated reader and a limited bandwidth, new architectures of battery-less backscattering-based communications have been considered. Among them, 5G appears particularly promising thanks to the large bandwidth, the interoperability among devices and the pervasive coverage. In this perspective, this paper proposes the first epidermal chemical sensor for the sampling of the human sweat and the monitoring of the pH. The devices communicate with the external reader through a frequency modulation of the backscattered wave, whose parameters depend on the measured analyte. Early simulations and tests corroborate the feasibility of the approach.

Boasting low cost, complexity, and energy consumption, scatter-based communications has emerged as a prime technology for real time sensing of spectral and environmental behaviors in contentious environments. Successful deployment of scatter networks require RF path loss modeling capability that does not readily exist in commercial tools.

This work uses the terrain-integrated rough earth model (TIREM) -- a knife-edge diffraction-based propagation engine -- to generate models for bistatic radio links. Using geographical information services (GIS) data, RF prediction maps are generated to determine regions of coverage that will support link establishment and is uniquely focused on smaller scale environment.

Prediction maps are generated to observe the effects of realistic environments on bistatic link receive power, SNR, and SIR, illuminating the concerns that face these sensor network topologies and making an argument for the use of tools like TIREM to generate quick, accurate information for researchers and designers.

This paper describes the design, manufacturing and range measurement of an UHF (ultra high frequency) RFID (radio frequency identification) tag to apply on a glass bottle filled with water. To achieve this, a free-space matched RFID antenna is studied and modifications are made in order reduce its size drastically and to turn it functional when applied to a bottle with water. Later, range measurement tests are made on the fabricated tag.

A microwave imaging approach for the detection of neck tumors is proposed in this paper. Specifically, a preliminary artificial neural network (ANN) is adopted for the reconstruction of the properties of a cross section of the neck starting from scattered electric fields. To this end, realistic neck phantoms are developed to test the feasibility of the proposed method. Several test cases are performed to evaluate the performance of the ANN to discriminate different size of the tumor and different position in the neck. The preliminary results indicate quite good detection capabilities.

Microwave Imaging (MWI) has been studied to aid early breast cancer detection. Current prototypes in more advanced stages of development include both monostatic or multistatic setups. However, multistatic configurations usually include a high number of antennas which consequently require complex and computationally-intensive signal processing algorithms to ensure a good target detection. We previously presented a novel approach using a dielectric lens which reduces the signal processing burden of multistatic setups, while ensuring good spatial resolution. In this paper, we evaluate this novel setup using an anatomically realistic breast phantom and its capability of selecting targets inside the breast. We show a successful detection of the targets using an artefact removal algorithm based on singular value decomposition when the Bessel beam is centered at the target location.

This study presents the design and the experimental validation of a slot-loaded antipodal Vivaldi antenna for to monitor liver microwave thermal ablation through microwave imaging techniques. The antenna's overall dimension is equal to 40mm×65mm, and its working bandwidth goes from 600 MHz up to 3 GHz, with the possibility to operate at a higher frequency. The antenna is designed to operate inside a coupling medium that allows to scale down the antenna dimensions, as well as to improve the coupling of the electromagnetic power to the tissue. The antenna's S-parameters well agree with the simulation result. Finally, the antenna proposed in this work shows the most compact aperture dimension, as compared with other similar antennas designed for biomedical applications, working within the same bandwidth.

In this work, we present a preliminary study of three classifiers - Linear Discriminant Analysis (LDA), Support Vector Machines (SVMs) and k-Nearest Neighbors (kNN) - to differentiate between malignant and benign tumors extracted from Magnetic Resonance (MR) images, based on their morphological features. The dataset in this study comprises 24 tumors: 12 malignant and 12 benign. Twelve morphological features were initially considered for tumor classification. The Mann-Whitney test was employed for feature selection, and the performance of the classifiers was evaluated with accuracy, sensitivity, specificity, F1-score and Matthew's Correlation Coefficient (MCC) metrics. kNN (with k=6 and Chebyshev distance) outperformed the other classifiers with an accuracy, sensitivity, and specificity of 87.5%, 83.3% and 91.7%, respectively.

This paper presents considerations on co-design and co-optimization of a chip-package to a near-field PCB antenna transition operating at K-Band frequencies. The transition and the on-PCB antenna are intended for use with a stepped FMCW radar chipset, operating in the frequency range from 16 GHz to 24 GHz. The target application is the realization of a large MIMO imaging array for breast cancer imaging. In this paper we first present the system level considerations. We describe the intended system itself, system partitioning, as well as the arrangement of antennas and radar transceivers. Next, we discuss in detail the antenna design. Unlike the classical free-space scenario, in this case the antenna radiates into the skin and fat tissue. Secondly, we show the package transition design considerations. The transition is realized in the embedded wafer level ball grid array (eWLB) packaging technology.

Tracking the characteristics of microwave-induced thermoacoustic (TA) signals is an emerging method for real-time monitoring of microwave ablation (MWA) performed with microsecond-duration microwave pulses. Extensive understanding of how tissue properties impact TA signal characteristics is necessary to enable the effective use of TA signals to monitor the evolution of an ablation zone. In this study, we investigate the impact of salinity content in water on TA signal characteristics that are generated as a result of pulsed microwave absorption. Experimentally measured TA signals are compared to computed TA signals using known salinity-dependent dielectric, thermal, and acoustic properties in a multi-physics simulation model. The predicted and observed trends with saline content are in agreement, and demonstrate the potential for monitoring a changing tissue environment during microwave heating by exploiting the thermoacoustic effect.

New technologies in a vehicle increase the effort for the safeguarding of electromagnetic interaction between novel bus-/communication systems (e.g. Automotive Ethernet 100Base-T1 and 1000Base-T1) and vehicle antennas. Characteristic transfer functions measured in the real vehicle environment with a vector network analyzer can be used as an approach to determine the electromagnetic interaction of wiring harnesses and antennas in the vehicle. In this contribution, several antenna structures and vehicle models are analyzed with respect to the induced emission signal at the antennas. The analysis thus allows a first insight into the electromagnetic interaction of a multi-antenna system in the application of a 100Base-T1 communication system. The advantage of different antenna structures for the multiantenna system in terms of the interaction with a wire harness is discussed.

An automotive 4x4 MIMO Antenna set for 5G mobile communication with decoupling- and matching circuit is presented which can be integrated in a symmetrical double shark fin. The antenna system with circuit is well performing in a low 5G-frequency band from 617 MHz up to 960 MHz as well as in a high band from 1.7 GHz up to 6 GHz. The decoupling circuit yields a transmission factor between adjacent antennas of about -10dB in the low band and less than -15dB in the high band. Matching is achieved with less than -6dB in the low band and less than -10dB in the high band. Measured and simulated scattering-parameter values are shown in comparison with each other. The decoupling and matching circuit yields low losses which can be shown by the total efficiency of the antennas depending on the frequency.

This paper presents a new wideband right-hand circular polarized antenna with a homogenous high Gain (4 dBiC) and a good-cross polar discrimination (XPD) over a bandwidth of 85 MHz. The proposed antenna is optimized for the L1-Band of the global navigation satellite service. The return loss between 1.525 GHz and 1.61 GHz is lower than -15 dB without the need of any matching circuit. The compact antenna structure is made of panel and can be fabricated easily by an industrial punch bending process.

Vehicular communication systems can be used for enhancing the safety level of road users by exchanging safety/warning messages. In this paper, we propose an antenna for a pedestrian-to-vehicular (P2V) device which provides safety service to road workers on the highway or road environment. A metasurface antenna system was fabricated and tested in the anechoic chamber. The device is worn close to the body of the road worker and at a distance of less than 200 mm. In this framework, the SAR has to be evaluated and compared to the threshold values recommended by standards. Experimental results showed that the proposed antenna, backed by a metasurface reflector, is an excellent candidate for P2V communications based on IEEE802.11p systems with desirable radiation pattern, polarisation, and safety limits. Finally, a comparison between our antenna system performance in terms of full coverage direction and other systems is done.

This paper presents fully integrated low-profile antenna systems for multiple-input multiple-output (MIMO) 5G and global navigation satellite system (GNSS) for L1/L5 frequency bands. The designs can be used on the vehicle's roof inside a low-profile housing due to its physical parameters and performance. Two samples are presented using HFSS simulation. The first sample shows the 5G MIMO integration performance with the L1 GNSS band while the second sample is integrated with the L5 GNSS band. The measurement results are discussed and plotted in terms of VSWR, passive isolation, and radiation patterns.

A novel synthesis method using an incident angle dependent impedance mapping for holographic multi-feed antennas is presented. In the proposed multi-beam synthesis, a individual merged impedance hologram for each feeding point is determined, which has the lowest impedance error to the corresponding analytical holograms. Subsequently, a non pixel-based genetic optimization is used to account for global error minimization across all feeds. The antenna is going to be realized on glass due its lower loss and dispersive properties compared to Teflon-based materials at mm-wave frequencies. In addition to the incident angle dependent hologram synthesis method, an appropriate sub-wavelength pixel has been design and optimized with enhanced anisotropic properties. The implemented holographic multi-feed antenna design has an antenna gain of 23.3 dBi and 23.0 dBi, a polarization purity of 23.0 dB and 20.3 dB and a side-lobe level of -18.5 dB and -19.0 dB with 2 feeds at 77 GHz.

In the framework of reconfigurable intelligent surfaces, it is of key importance to be able to tailor spatially and temporally with large flexibility the impinging radio-wave signals. In this context, conventional metasurfaces relying on spatial gradients to manipulate the optical wavefront are fundamentally limited on their overall efficiency to reroute the impinging waves towards arbitrary directions in reflection and transmission. In addition, due to their fastly varying profiles of surface impedance, metasurfaces usually require high-resolution fabrication processes, limiting their applicability and bandwidth of operation. Metagratings, i.e., periodic or locally periodic arrays operated in the few-diffraction order regime, on the contrary can manipulate electromagnetic waves with unitary efficiency even in the limit of extreme responses. In this talk, we will review the physical mechanisms behind the functionality of metagratings and provide an outlook of the recent progress in this field of science and technology, of particular relevance to reconfigurable intelligent surfaces.

A reconfigurable intelligent surface (RIS) is capable of manipulating electromagnetic waves with its flexibly configurable unit cells, thus is an appealing technology to resist fast fading caused by multi-path in wireless communications. In this paper, a two-path propagation model for RIS-assisted wireless communications is proposed by considering both the direct path from the transmitter to the receiver and the assisted path provided by the RIS. The proposed propagation model unveils that the phase shifts of RISs can be optimized by appropriate configuration for multi-path fading mitigation. In particular, four types of RISs with different configuration capabilities are introduced and their performances on improving received signal power in virtue of the assisted path to resist fast fading are compared through extensive simulation results. In addition, an RIS operating at 35 GHz is used for experimental measurement. The experimental results verify that an RIS has the ability to combat fast fading and thus improves the receiving performance, which may lay a foundation for further researches.

Huygens' metasurfaces provide a platform for realizing low-profile antennas without sophisticated feeding networks. In particular, they can synthesize radiating apertures by passively transforming the incident fields. In this paper, we summarize recent progress on the field of beamforming and beamsteering with Huygens' metasurfaces. Several strategies to overcome the limitations posed by the passivity of Huygens' metasurfaces and to achieve arbitrary beamforming are explored. Furthermore, ways to integrate tunable metasurfaces with leaky-wave antennas are discussed with the purpose of obtaining electronically steerable far-field patterns.

In this paper we review our works on reconfigurable intelligent surfaces over the past 10 years, summarize our main results, and underline the problems we have faced while trying to push this idea towards applications. This allows us give a pioneer's point of view of the future of RIS, that we foresee as a technology that should be as autonomous as possible.

The use of reconfigurable intelligent surfaces (RIS) for optimization of propagation channels is one of the currently actively studied techniques for improving the efficiency of the next generation of communications systems. In this work, we combine the physical optics approximation and the theory of diffraction gratings to derive simple analytical formulas for far-zone fields reflected and scattered by anomalously reflecting metasurface panels mounted on walls. In the talk, we will present numerical examples, illustrating the difference in performance of conventional phase-gradient reflectors (reflectarrays) and optimized nonlocal metasurface reflectors.

A method is presented here for ray-representation of the scattered field from polygonal, metasurface (MTS)-based Reflective Intelligent Surfaces (RIS). The method is-based on the use of an infinite periodic problem for finding the current distribution over the RIS aperture, which is eventually windowed for calculating the radiated field. Stokes theorem is applied on the windowed radiating aperture to find a closed form representation of the radiated field in terms of rays. The formulation developed here is in the far zone; it is however suggested how it can be extended to the Fresnel region by introducing proper Fresnel transition functions.

We introduce a closed form for the solution of the Stochastic Green functions in closed chaotic environments. The solution is an alpha-stable random distribution whose parameters (stability, skewness, scale and location) depend on the distance between source and observation, frequency and dissipation in low dissipative problems. Excellent comparisons with infinite-sum stochastic Green function and numerical problems is shown, which will allows, in the future, the use of simple stochastic expressions in Surface Integral Equation methods for chaotic environments.

Integral equation methods are widely used in computational electromagnetics (CEM). Galerkin and Nyström are two possible schemes to discretize any integral equation. Among the CEM community, Galerkin is by far the most common scheme used. Nyström has some advantages when dealing with second kind integral equations, nevertheless it has some disadvantages when dealing with multiscale geometries. In this paper we propose a fix for that and apply this to the Charge-current integral equation.

Among the most mature approaches to stabilize the electric field integral equation (EFIE) for low frequencies are quasi-Helmholtz projectors. In this work, we show how to adapt these projectors such that the right-hand side can be discretized in a stable manner on multiply-connected geometries, preventing otherwise occurring catastrophic round-off errors. To this end, an approach to combine the quasi-Helmholtz projectors with a scalar-potential representation of solenoidal functions is presented. Furthermore, we provide a strategy to efficiently compute the corresponding projectors via the Schur complement, all of which is corroborated by numerical results.

We use the Method of Moments to study the iso-frequency dispersion curve of conducting patches of general shape printed on a grounded dielectric substrate. To accelerate the method, we use a specialized interpolation technique to rapidly evaluate the periodic impedance matrix of the system for many different phase shifts between consecutive unit cells. The interpolation procedure is based on the extraction of an easy-to-compute rapidly varying term and the interpolation of the smooth remainder. Using the proposed method, computing the periodic impedance matrix for a new phase shift is a matter of milliseconds without sacrificing the accuracy. To validate the method, we reproduced results that are available in the literature.

This paper presents a model developed to numerically determine the radiation pattern presented by a given geodesic lens. A simplified model describing the trajectory of a TEM-mode wave through the lens was required as a time-efficient alternative to commercial software. Geometrical optics have been used to approximate the ray trajectory from the source to the aperture of the lens. The power conservation in ray tubes is then used to evaluate the amplitude of the electric field in the aperture, knowing the distribution at the source. The Kirchhoff diffraction formula is finally numerically approximated to evaluate the far-field. Three examples have been simulated with our algorithm and compared with full-wave simulations. We demonstrate that our assumptions provide a good agreement with full-wave simulation while reducing significantly the computation time, thus providing an efficient method for design optimization. Most notably, this more general formulation may be extended to non-rotationally symmetric lenses.

In this work, we propose Monte Carlo sampling as a technique to avoid communication overhead in the numerical solution of complex electromagnetic scattering problems. The method is based on statistically sampling a formal representation of the solution of the scattering problem, based on a modified Born series. The sampling process can be independently carried out in different processors with no need for communication between them. This lack of communication makes the algorithm suitable for massively parallel computational environments.

With the need for ever faster codes, a limiting factor that must be dealt with is the accurate yet efficient evaluation of interaction integrals between the more problematic near-field elements. Several recent works have together shown that all evaluations of source potential integrals and their derivatives for the most common bases and elements can be reduced to the evaluation of boundary line integrals; these can be evaluated by Gauss-Legendre quadrature, though integrand-smoothing transforms are often needed to accelerate their computation. In this paper, we modify the reported approach to eliminate cancellation errors in the line integral integrand, reinterpret the integral as a vertex function, and study the scalar potential integral form under the sinh transform and static subtraction acceleration methods.

We consider a method of evaluating Galerkin matrix elements of surface integral equations involving the normal derivative of Green's function, for basis functions supported on parallel planes. Our method uses the previously introduced representations of integral-equation kernels as Laplacians of non-singular auxiliary functions, and Gauss's theorem resulting in conversion of surface integrals to integrals over triangle perimeters. However, unlike in the previously considered kernels, the discontinuity (across the plane of the basis function support), of the normal derivative of Green's function affects also the corresponding auxiliary functions. We examine their behavior and its effects on the numerical evaluation of the line integrals. Our analysis allows us to improve the accuracy of the numerical line integration and avoid instabilities associated with cancellation of large terms in the line integrals. The derived Laplacian representation is also used to obtain analytic expressions for the double line integrals, in terms of elementary functions.

In this work we present the combination of the JMCFIE formulation in synergy with the discontinuous Galerkin surface integral equation method for the electromagnetic analysis of piecewise homogeneous objects. The interfaces between different materials can be independently modeled, without need to add restrictions at the junctions between them. The proposed scheme avoids the need to joint and delete extra coefficients to enforce the boundary conditions at the multi-material junctions. Numerical experiments will be shown to illustrate the great flexibility of this approach for the solution of composite objects with multiple high contrast materials in contact.

In this talk, I will review our latest progress towards the design and implementation of metamaterials and metasurfaces that can manipulate electromagnetic waves in exotic ways by operating at the quantum limit. I will discuss various examples of opportunities enabled by quantum engineering metasurfaces, discussing coupled nanocavities supporting embedded eigenstates that enable single-photon trap-and-release mechanisms, nonlinearity-based isolators for guided light and free-space radiation, and giant nonlinearities in tailored metasurfaces. I will also discuss polaritonic systems that enhance light-matter interactions through quantum phenomena. During the talk, I will discuss opportunities, potentials, challenges enabled by metamaterial approaches to manipulate quantum and classical electromagnetic waves.

Recently, we have seen an extensive and growing interest in leveraging reconfigurable intelligent surfaces towards smart radio environments. One key question arises on how to efficiently select the phase configuration that produces a desired reflective wavefront. In this work, we proposed a physics-based optimization approach inspired by the quantum mechanical physics of correlated spins. The new idea is grounded on the isomorphism between the electromagnetic scattered power and Ising Hamiltonian. Thereby, the problem of optimizing phase configuration is converted into finding the ground state of the target Ising Hamiltonian. Under this framework, we successfully demonstrated the feasibility of combinatorial optimization for weighted beamforming and diffusive scattering applications.

In this work, within the framework of Boundary Integral Equations (BIEs) and the Boundary Element Method (BEM), we present a novel modeling scheme that considers the multiple scattering of light by metallic nanoparticles. Different from the classical treatments where the optical properties of metals are captured by the local response model, we describe the metals by a nonlocal model, i.e., the hydrodynamic model. This nonlocal model is very important for the cases where the nanoparticles are of deep-nm sizes or the nanoparticles have a deep-nm feature, e.g., a dimer with a gap size of a few nm's. To fully consider the nonlocal effects, we write down the BIEs and implement the BEM for the following three different interface configurations: the local - local interface, i.e., an interface separating two media described by the local models; the local - nonlocal interface, i.e., an interface separating one medium described by the local model from another medium described by the nonlocal model; and the nonlocal - nonlocal interface, i.e., an interface separating two media described by the nonlocal models. The results from our BEM implementation are compared to the analytical ones from the Mie theory, and a good agreement is demonstrated.

Advances in additive manufacturing techniques and materials have enabled the fabrication of complex 3D microwave scatterers that until very recently were beyond the reach of experimental science. These show powerful isotropic scattering behaviour, with negligible dependence on incident angle or polarization for several resonant modes. These scatterers have applications in enhancing the radar signature of small objects such as drones and satellites and in controlling the radiation pattern of antennas.

Additive manufacturing makes possible the rapid design and testing of gradient index (GRIN) lenses. GRIN lenses, whose refractive index profiles are spatially-varying, have been shown to improve the gain of antenna systems while in more compact forms. However, optimization of the GRIN lens profiles is difficult because the lenses can be many wavelengths wide, and the simulations slow to compute. Furthermore, the large number of design variables makes solving the GRIN lens profile a challenging problem. However, these problems can be remedied using adjoint sensitivities to compute the gradient for every design variable in only two simulations. Then local optimization approaches can follow these gradients to rapidly converge to a good candidate solution. To demonstrate the efficacy of the approach, a GRIN lens design was optimized to have the same measured broadside gain as a 20 dB standard gain horn.

A device for detecting liquid chemicals of various permittivity using a 3D Printed frequency selective surface (FSS) is proposed. The sensor is an array of square loops on a square unit cell with trenches dug in the dielectric material around the loops. The trenches allows deposition of the liquid chemicals to be detected. The variation in the dielectric characteristics of the liquids in the trenches produces a change in the resonance frequency of the FSS. Transmission coefficient is measured to evaluate the resonance frequency due to each liquid chemical. Butan-1-ol, Propan-2-ol, Ethanol and Methanol were added to demonstrate the sensing technique. Good agreement was found to exist between simulated and measured results. The envisioned detector could be used in a laboratory or in chemical industry where liquids can fall into the trenches for detection purpose. 3D printing allows for the rapid fabrication of the structure which can be disposable.

This paper discusses the research related to 3D printed radiofrequency (RF) devices, using fused filament fabrication, carried out at Loughborough University. Different multidisciplinary aspects include the ability to 3D print unique shapes, the ability to tailor the infill to make functionally graded and heterogeneous substrates, characterizing the dielectric properties and how these materials can be used for antennas and other RF designs.

Advanced additive manufacturing (AM) technology enjoys the advantages of fast-prototyping, low-entry-cost, and in-house short-run manufacturing, which empowers millions of start-ups and companies with demanding confidentiality and accelerated innovation. The advancement of AM technology will circumvent the limitations of traditional 3D printed microwave circuits and antennas. This talk aims to present the fundamental knowledge about AM technology and its capability in microwave/millimeter-wave/terahertz circuits and antenna designs. This article presents the state-of-the-art 3D printing technologies and their applications in the millimeter-wave, and sub-terahertz designs, including meta lenses, frequency selective surfaces, waveguides, and antennas.

The Far-field radiation performance of quintessential compact resonant cavity antennas (CRCAs) is compromised because of even transmission through uniform superstrate resulting in non-uniform aperture phase distribution. Phase varying superstrate (PVS) can be used to improve phase non-uniformity and even achieve wideband directional characteristics with small footprint. This paper presents three different PVSs using customization ability of additive manufacturing (AM) and distinct fabrication approaches for CRCA. These three approaches are based on height variation, infill variation and perforation size variation in the radio-frequency graded acrylo-butadiene sterene (ABS) material. Each PVS comprises three dielectric regions with different transmission characteristics for local phase variation. Uneven transmission through PVSs remarkably improves aperture phase of CRCAs subsequently increasing peak directivity (>17 dB) and 3dB directivity bandwidth (>50%) whilst maintaining small footprint of radius ≈0.84λ L. All three PVSs can be developed at a cost less than US$ 1.25 without compromising antenna performance.

In this article, the experimental verification of a 3D-printed radial GRIN lens operating in the Ku-band between 12 to 18 GHz is presented. The GRIN lens can be found useful in high directivity and beamforming antenna applications. The design of the radial GRIN lens is based on a new closed form expression for the refractive index which is derived by geometrical optics. The GO-based formula is proved to achieve a minimum phase error that can lead to an increased lens aperture efficiency. The challenges that arise from the practical realization using 3D printing technology are discussed. Measurement results of the 3D printed lens are presented and compared with simulations, showing good agreement. Two antennas of low-medium gain are used, a 5 dB open-ended waveguide antenna and a 15 dB horn antenna. A maximum gain of 25 dB is achieved with a lens aperture of 7.2λ diameter at the highest frequency.

In recent years, additive manufacturing has evolved to become a key method of prototyping devices across many industrial sectors including electromagnetic systems such as antennas. The range of materials that can now be deposited by 3D printers has expanded the suite of devices that can be rapidly manufactured. In this paper we will present two electromagnetic lenses that demonstrate the advantages of multi-material 3D printing, where a number of different dielectric materials are used to design functional devices with interesting properties. The first example is a frequency dependent dual focusing lens design through topology optimization, using two different dielectric filaments. The second is a compressed Luneburg lens that theoretically requires a continuous permittivity gradient from 7.8 in its centre down to 1 on the surface, and is realised by printing with a total of five different dielectrics.

Phased arrays are increasingly used in communication systems to benefit of their full beamforming capabilities. However, some of its limitations are related to the limited coverage, due to the antenna elements that are used today present some directivity. In this paper, two radiating structures with enlarge beamwidth are presented, using principles of lens antennas that can be produced with the support of 3D printing, and its most popular materials. Both solutions start from a microstrip antenna, and a multilayer structure operating as a lens and validating the principle at 7.8GHz, allowing to increase beamwidths by 80% for the ϕ=0º plane and 40% for the ϕ=90º plane.

In the era of the Internet of Things and wearable electronics, printing techniques, such as screen printing, are becoming popular because of their lower costs and mass manufacturing abilities. However, most of the previous work has been done on printing metallic patterns and not the substrates. In this paper, we introduce a custom screen printable dielectric ink, which provides lower loss even at millimeter-wave bands. With the help of dielectric ink and a custom silver nanowires-based metallic ink, a multilayer fully screen-printed fabrication process has been developed. To demonstrate the efficacy of the proposed inks and the multilayer printing process, a stacked patch antenna is designed and fabricated for the mm-wave band. Despite a new fabrication process, the measured results show a decent antenna performance for flat and bent positions where the input impedance is matched from 26.5-30 GHz and a maximum gain of ~8dBi has been achieved.

This paper presents a non-zoned discrete dielectric lens comprising two or three matching layers to reduce the 50-110 GHz frequency range reflections. Based on Chebyshev and binomial multi-section transformers, the designed models use matching layers at the top and bottom. In addition, the presented designs use pins instead of the conventional slots for the matching layers, thus easing the manufacturing process. The results show that the broadband realized gain obtained using the proposed design is higher for both the two- and three-layer design than the commonly used quarter-wave transformer. A Binomial lens with two matchings layers using 38 unit cells is fabricated and illuminated by an open-ended waveguide to validate the simulation results obtained using CST Microwave Studio. The fabrication process uses stereolithography additive manufacturing.

The design of a Half-Maxwell Fish-Eye lens antenna fully made with 3D printing, including its feed, is presented. For the feed, a dielectric resonator antenna with a symmetrical radiation pattern was specifically designed. This antenna is also made with 3D printing technology and it is integrated with the lens. The lens has 10 layers with different permittivities that are implemented with two commercial filaments by varying the infill percentage. The design was made for a 28 GHz central frequency and has the capability for scanning or multibeam performance.

The Multimodal Transfer Matrix Method (MMTMM) is a hybrid approach that efficiently computes the dispersion relation of a periodic structure. It is able to retrieve both the phase shift and attenuation constant of any arbitrary structure susceptible to be analyzed by means of commercial simulators. Here, we propose the use of this method in order to get a physical insight of periodic structures possessing higher symmetries. The MMTMM is here explained and corroborated with two different structures: a glide-symmetric dielectric-filled corrugated rectangular waveguide and a three-fold twist-symmetric bricks embedded in a dielectric waveguide. The first structure allows for the propagation of backward modes below the hollow waveguide cut-off frequency, whereas the second one has handedness selection.

We show the relation between reflection and glide symmetry in periodic lossless waveguides and the existence of various orders of exceptional points of degeneracy (EPDs). We use an equivalent circuit network to model each unit-cell of the waveguide. Assuming that a coupled-mode waveguide supports N modes in each direction, we derive the following conclusions. When N is even, we show that a periodic waveguide with reflection symmetry may exhibit EPDs of maximum order N. To obtain a degenerate band edge (DBE) with only two coupled waveguides, reflection symmetry must be broken. For odd N, N+1 is the maximum EPD order that may be obtained, and an EPD of order N is not allowed. We present an example of three coupled microstrip transmission lines and show that breaking the reflection symmetry by introducing glide symmetry enables the occurrence of a stationary inflection point (SIP) which is an EPD of order three.

Glide symmetry is a low-cost design change that enhances many properties of metallic waveguides, such as the achievable stopband, the frequency and spatial dispersion, or the effective density. But the multi-modal coupling in glide-symmetric waveguides makes it difficult to model them efficiently. This paper presents a wideband homogenization technique based on a quasi-static approximation. It yields a closed-form formula for the effective refractive index of holey glide-symmetric parallel- plate waveguides. This formula enables fast analytic studies for the properties of these waveguides, such as maximum density, isotropy, or effective constitutive parameters.

This paper demonstrates the practical feasibility of an open-ended parity, time-reversal, duality symmetric edge waveguide structure. This includes perfect electric and perfect magnetic based parallel plate waveguides. For practical implementation, a mushroom structure is used to emulate the perfect magnetic boundary conditions. Two kinds of edge waveguides are implemented and numerically analyzed. Results concerning the return loss and the ability to confine the EM field near the edge waveguide at the open-end are shown and compared.

In this paper, we propose a technique based on integral equations, the periodic Green's function, and the method of moments discretization to analyze the dispersion diagram of non-canonical glide-symmetry unit cells. The technique is combined with a root finder approach to automatically identify the values of the wavevector that make the unit cell resonant. The proposed technique is tested on a glide fully metallic implementation of a Luneburg lens.

Periodic structures with higher symmetries have the potential to unlock many enhanced properties of microwave components and enable the development of novel components. The dispersion properties of these structures, however, are often not spatially isotropic which limits their application in some cases. For this reason, we focus on the analysis of holey structures with glide symmetry and their isotropic properties. Through analysis of typical holey structures and different lattices we demonstrate which design directions are to be used when one of the priorities are good isotropic properties and where are the limits of considered structures.

The paper targets the problem of human motion detection using Wireless Local Area Network devices (WiFi) equipped with pattern reconfigurable antennas. Motion sensing is obtained by monitoring the body-induced alterations of the ambient WiFi signals originated from smart antennas supporting the beam-steering technology, thus allowing to channelize the antenna radiation pattern to pre-defined spots of interest. We first discuss signal and Channel State Information (CSI) processing and sanitization. Next, we describe the motion detection algorithm based on Angle-of-Arrival (AoA) monitoring. Proposed algorithms are validated experimentally inside a large size smart home environment.

The authors have developed the Multipath-RTI (radio tomographic imaging) technique based on millimeter-wave (mm-wave) radios such as 5G mobile and WiGig LAN systems. Mm-wave radios can realize a highly accurate device-free localization (DFL) for smart home/smart building applications by utilizing the features that mm-wave radios usually have high delay and angle resolution, and thus is capable of separating the multi-path components (MPCs). The Multipath-RTI can drastically reduce the number of sensor nodes by using the virtual nodes created by multipaths. However, there are technical challenges to handle the multipaths and corresponding pathways. This paper proposed a practical data processing scheme for Multipath-RTI and presented some actual imaging results for DFL using double-directional channel sounding measurements.

Wi-Fi channel state information (CSI) has been widely utilized in various motion sensing applications such as motion detection, recognition, localization and tracking. Comparison with Doppler frequency, propagation delay is unreliable due to a non-synchronization between two Wi-Fi stations, thus it is hardly utilized for motion sensing. Since the CSI B2B calibration in the previous work introduced a form of synchronization via a cable channel, the propagation delay has become utilizable. In this paper, a performance and reliability of the CSI propagation delay will be validated as well as addressing the source of delay offset due to B2B calibration. In addition, applicability of utilizing propagation delay in a person falling scenario will be demonstrated as one of the motion sensing application.

In this paper, several posture models is set up in the reverberation chamber, and the effects of human body on the electric field distribution is quantitatively evaluated by numerical simulation at 2.45 GHz. Specifically, 12 observation points are set up, and the simulation is performed by changing posture models and stirrer angles. The simulation results show that the electric field amplitude becomes less than 1/100 and the electric field homogeneity deteriorates with posture models. Also, the results of the analysis of variance show that the influence of the observation points is smaller compared to the previous study simulated at 403.5 MHz. Furthermore, it is found out that the electric field homogeneity deteriorates as the number of observation points increased. Future studies includes evaluating the effects of various postures and comparing them with actual measurements.

We have a closer look at widely linear beamforming (WLB) for full-duplex Joint Communication and Sensing (JCAS). WLB is a powerful method for mitigating the effect of IQ imbalances in array radiation. In full-duplex JCAS, the transmitting aperture radiates multi-beams focusing towards the communication user and the sensing target, while simultaneously the receiving aperture receives sensing signals. When applying WLB intended for interference mitigation between the transmitting and receiving apertures, mirror beams often occur and degrade the mitigation effect. In this paper, we propose to use virtual displacement of array elements during local optimization in WLB to further reduce the mirror beams. The virtual displacement is to deviate the antenna elements virtually in WLB optimization process and, in the numerical analysis, we show that this can be a solution for interference mitigation while we use uniform arrays in practice. This approach can facilitate the usage of modular hardware for JCAS.

The electromagnetic clutter mitigation is increasingly demanded for achieving the indoor identification and long-range reading of wireless and passive sensor tags. In this paper, a new Polarization Diversity scheme is proposed to reduce the clutter and consequently, to increase the reader-to-tag separation distance. The proposed wireless tag is a two-port patch antenna loaded by proper passive impedances. When illuminated by a circular polarized electric field, the proposed tag backscatters a linear or circularly polarized electric field, depending on the choice of four passive load impedances. This polarization conversion is then easily controlled, and could be advantageously implemented to improve the existing RFID systems by increasing reader-to-tag separation distance in cluttered environments.

This paper presents a new weighting method that can be used for designing antenna clusters. The proposed weighting method performs a compromise, which provides a moderate and practical way of taking into account both the scattering parameters of the antenna cluster and the efficiencies of the individual antenna elements. Meanwhile, it does not require the detailed information nor the volume integral of far-field radiation patterns at each frequency point. In order to validate the proposed weighting method, an antenna cluster consisting of four inverted-F antenna (IFA) elements for mobile handset devices operating at 700-960 MHz is designed. The total active reflection coefficient (TARC) and the total efficiency of the antenna cluster are compared with the existing methods.

This paper proposes the design of a high-gain, wideband, directive, and compact circular array composed of 5 symmetrical radiating elements (1 fed and 4 parasitic elements). The possibility to implement an electronically beam-switching capability over the horizontal plane is studied. Thanks to the superdirectivity principle, the proposed closely spaced parasitic antenna array achieves a maximum gain of 10 dBi steered in four directions on the horizontal plane and a minimum gain of 9 dBi in the whole horizontal plane. The proposed antenna achieves a stable gain > 9dBi in the frequency band 758-803 MHz, which is interesting for sub-GHz 5G applications.

This paper presents the design, manufacturing, and measurement of a novel substrate integrated waveguide (SIW) pedestal filtering antenna solution for use in 5G New Radio sub-6 GHz communications. Miniaturization is achieved through the use of SIW pedestal resonators and integration of the radiating element into the filter design, resulting in higher order suppression. The design generates a third order filtering response utilizing SIW pedestal resonators and a patch antenna element. The manufactured SIW pedestal filtenna achieves a 10 dB return loss bandwidth of 4.29 % about a centre frequency of 3.63 GHz, and a boresight gain of 3.66 dBi. Additionally a 1x4 linear array is measured, demonstrating the applicability to 5G radio frequency front-ends.

Vulnerable road users such as cyclists and pedestrians are now being increasingly integrated into connected driving issues. The focus of this paper is on cyclists with pedelecs as one group of vulnerable road users. Direct sidelink communication between cyclists and cars is also examined. In this study we present measurements obtained with commercially available on-board units operating at 5.9 GHz and based on LTE V2X. The antennas are connected to the OBU in different constellations using transmit and/or receive diversity. Simulations are used to support the measurements. For the intersection example scenario we observed reliable communication between a car with a distance of 25 m and a pedelec with a distance of 60 m towards the intersection. In a rural scenario, the communication range can be more than 400 m. However, the results depend highly on the antenna position on the pedelec.

This paper studies the EMF (electromagnetic field) exposure distribution for a specific deployment scenario. This developed novel approach based on a Monte-Carlo (MC) approach took into account the non-uniform user distribution and its corresponding projection to provide a realistic EMF exposure assessment for a particular coverage area of the 5G base station. A suburban area with relatively complex user distribution was selected to study the exposure distribution by the proposed method. The simulated results derived by the MC method show that considering the user distribution will reduce the user-related E-field exposure distribution under the given configuration by more than one half when compared to the traditional conservative deterministic approach. Moreover, the MC method demonstrates a more detailed exposure distribution feature corresponding to the specific active user distribution. It presents a reliable basis for power control when considering the trade-off between exposure evaluation and service quality.

This paper presents a low-profile 5G phased array with improved radiation properties for smartphone applications. By modifying the structure of antenna elements from conventional slots to air-filled slot-loop resonators (with the same thickness of the substrate), the array is capable to provide high-performance radiation beams at different scanning angles, even though it is designed on an FR-4 substrate. The array contains eight slot-loop radiators. The employed elements have low profiles with discrete-feeding ports and they operate at 21-23.5 GHz. Moreover, the coupling of the radiators is less than -15 dB at the centre frequency. Well-defined and quasi end-fire radiation, good efficiency and gain levels, wide beam-steering wide operation band are the promising characteristics of the introduced array which make it suitable for smartphone applications.

Agriculture 4.0 is going to represent a massive deployment of sensors, so efficient planning of radiocommunication systems in this type of environment will be necessary. In this work, the measured path loss in a LoS condition, with the transmitter and receiver heights below the trees height, at a citrus plantation in the 1800 MHz, 3.5 GHz and 28 GHz frequency bands using a two-ray model in the vertical plane and the FI (Floating Intercept) and the CI (Close-In reference) slope models is analysed. Results show that, in the 28 GHz band, the direct and reflected-from-soil contribution may be enough to estimate the path loss for all the measure distance range, however, in the 1800 MHz and 3.5 GHz bands the multiple-scattering contributions from trees need to be considered after some distance between the transmitter and receiver. Furthermore, a guiding effect has been observed only in the 1800 MHz band.

Channel estimation is challenging for millimeter-wave (mmWave) communications because of the use of hybrid architecture and massive multiple-input multiple-output (MIMO) technology. By utilizing the sparsity in the angular domain, conventional on-grid compressive sensing methods can efficiently recover the channel state information (CSI). However, the channel estimation accuracy is severely affected by the off-grid errors and the selection of grid angles. The off-grid compressive sensing methods and the non-uniform grid angles can improve the channel estimation accuracy. In this paper, we investigate the impact of the non-uniform grid angles for the off-grid compressive sensing methods and the on-grid compressive sensing methods. We propose to employ the orthogonal matching pursuit (OMP) algorithm with interior point (IP) method based off-grid error mitigation to implement the channel estimation using the selected angle design. The simulation results demonstrate the advantages of the proposed off-grid compressive sensing method and show the impact of the non-uniform grid angles.

This paper presents, the results of wideband measurements of several common building material conducted at 28 GHz, and 39 GHz in co-polar and cross-polar alignments to investigate the reflection and penetration loss at different incident angles using the wideband channel sounder developed at Durham University and narrow-beam lens antennas with 4.5 degrees beamwidth. The results show that, the lowest value of penetration loss was when the transmitter and receiver antennas are perpendicular on the material, and it was more than 30 dB (co-polar) and 20 dB (cross-polar) at angles greater than 10 degrees on either side from the zero angle for most of the tested materials.

Several models using deep neural network (DNN) have been proposed to estimate the path loss characteristics in the urban macrocell (UMa) environment, most of which use the height of buildings around Tx and Rx as input images to the convolutional neural network (CNN) part. However, buildings between Tx and Rx affect the path loss characteristics more than the buildings surrounding Tx and Rx, since the over-rooftop propagation becomes dominant when a Tx antenna is installed higher than the surrounding buildings. In other words, the DNN in these models does not consider the propagation paths over rooftops. If such paths were considered, it would be possible to improve the estimation accuracy. In this work, we propose a new model that uses the side-view image of a building on the straight line between Tx and Rx as input, in addition to the conventional top-view image. We then evaluate the effect using measurement data, the RMS error of the proposed model was 5.63 dB, while that of the conventional model was 9.46 dB.

This paper presents eight by eight MIMO measurements in a factory environment for both line of sight (LoS) and non-line of sight (NLoS) scenarios at 25 GHz using eight directional antennas at the transmitter and at the receiver with the custom-designed channel sounder developed at Durham University. The data were analysed to estimate the Rician the K-factor, angular spread, root mean square (rms) delay spread. The 50% and 90% values of the rms delay spread values for a 20 dB threshold are presented for both scenarios. The MIMO channel capacity is also estimated for different signal to noise ratios.

With the recent growth of computing resources, the construction of large-scale cyber-physical systems (CPS) becomes feasible, and they are expected to be an indispensable infrastructure for future product development. In the CPS, the physical information is gathered and utilized for the simulation in the virtual space. And finally, they will be utilized for various smart managements of the physical system. Because wireless communication is now an essential function in many systems, the simulation technique of the propagation channel becomes quite important. There are several types of research that utilize the point cloud data of the environment for the radio propagation simulation. However, the usage of the point cloud data is not so straightforward because it generally includes large noise, and points are not taken at constant spacing. It prevents from generating surface mesh data which is needed in the simulation. In this paper, we propose the channel prediction method by the aperture field integration method (AFIM) approach. In the proposed method, the spatial spectrum of the surface electric current is calculated, the scattering waves are represented by the superposition of several plane waves. The noise of point cloud data can be eliminated by filter.

A multifunctional, cost-effective, and easy to fabricate T-shaped patch antenna is presented, resonating in the frequency range of 18 - 25 GHz when evaluated without sample and resonant frequency in a range of 2.5 - 9 GHz when sample layer is introduced as superstrate, having a broad range of applications in the field of chemical and biomedical sensing. The sensor layer is the topmost layer with a T-shaped patch antenna underneath with substrate and ground plane, respectively. Ethanol, Methanol, and edible fat solution samples are investigated for concentration sensing. The design demonstrated consistent behaviour of increase in resonant frequency by the value of at least 150 MHz with an increase in the concentration of Ethanol and methanol. In the case of edible fat, the resonant frequency increased by a value of 10 MHz with an increase in the concentration of edible fat in the sample layer.

In this paper, we present a feasibility study of an innovative theranostic system for non-invasive detection and treatment of malign neoplasms by using a radio-frequency magnetic field. The proposed hardware system, operating at 3 MHz, consists in a resonant spiral coil coupled to an unloaded concentric probe loop. The tumor detection is achieved by measuring the amplitude shift of the probe input impedance while scanning the region of interest. This hardware configuration has the main purpose to produce a focused and homogeneous field distribution, which improves the device resolution during the imaging procedure; conversely, in the ablation treatment, it produces a focused heating precisely directed towards the previously detected tissues, preserving the surrounding healthy regions. The main advantages of the proposed system, beside the relatively low-complexity instrumentation, also include the possibility to reducing the time of diagnosis and the invasiveness for the patient, to increase the therapy effectiveness.

A microwave sensor to safely measure quality of muscle tissue for diagnosis and screening of diseases and medical conditions characterized by fat infiltration in muscle is presented. Fat infiltration in muscle may be seen by a lower dielectric constant of muscle at microwave frequencies corresponding to the large contrast between fat and muscle tissues. A planar resonator based on a bandstop filter and optimized to noninvasively interrogate muscle in the thigh on tissue quality is proposed. Currently, a study based on clinical trials is carried out, and, here, we present a preliminary correlation between skin and fat thicknesses and rectus femoris cross sectional area (CSA) measured with ultrasound and the proposed sensor's resonance frequency. CST simulations based on the ultrasound information guide the analysis. We see that although there are signs of a potential correlation between CSA and resonance, skin and fat variability is still an issue to overcome.

In this paper, we present an innovative radiating system able to produce a focused treatment for transcranial magnetic stimulation applications. The proposed configuration is based on a non-diffractive Bessel Beam launcher as radiating device. The launcher consists in five concentric planar spiral coils, working at 3 kHz, singularly fed with a proper current amplitude and phase. In this way, a Bessel-like non-diffractive magnetic field distribution can be recreated so that a focused induced electric field inside tissues can be generated. Such peculiar field distribution can find interesting applications for Transcranial magnetic stimulation (TMS), since extremely focused and accurate stimulation can be performed. The numerical results obtained through full-wave simulations show a good spatial resolution and focalization, in term of induced electrical field inside brain tissues at different depths. Such preliminary results suggest the possibility to overcome the single coil performance, encouraging further analysis.

Terahertz (THz) radiation has remarkable potential in the medical area as a non-ionizing, non-invasive, and label free method, especially in the early detection of cancer. Skin tumors typically have a higher water portion than healthy tissues, and this can be reflected in the electromagnetic parameters. In this work, we have investigated artificial human tissue with basal cell carcinoma (skin cancer) and explored the functionality of the anti cancer drug in the treatment process. The measurement is done in frequency range of 0.2 to 1.5 THz. In comparison with the artificial normal tissue, the results are in adaption with previous works and enriches the database of THz characterisation of cancer cells. Obtained THz electromagnetic properties of treated cancer can open new windows to boost the precision of diagnose and prevent skin tumours at the early stage

We describe a low-cost setup developed to carry out SAR measurements on a human phantom. The development comprises: a human phantom manufactured using a modified workflow from the mannequin industry, liquid preparations using recipes found in the literature, a system for the transmission and reception of RF signals, a system for tracking the position of a field probe during the scanning, which is carried out manually, and a system for the integration and post-processing of the measured data. Preliminary validation results demonstrate good performance for all the blocks described. Detailed results from an underway measurement campaign with these blocks will be presented during the conference.

Cooperative localization fills the gap in scenarios where global navigation satellite system (GNSS) reception is denied or impaired. Position and orientation information is then often provided based on signal round-trip time (RTT) and direction-of-arrival (DoA). Obtaining a meaningful RTT requires calibrated transceiver group delays, and accurate DoA estimation requires antenna calibration. Usually, such calibrations are performed once before operation. However, calibration parameters can change over time, e.g. due to varying temperature of RF components or reconfigurable antenna surroundings. To cope with that, we propose to estimate antenna responses and ranging biases simultaneously with positions and orientations by simultaneous localization and calibration (SLAC). We derive a SLAC algorithm based on Bayesian filtering, which is suitable for arbitrary antenna types. The algorithm is evaluated with measurement data from robotic rovers. We show, that ranging and DoA performance is improved considerably, leading to better position and orientation accuracy with SLAC.

Adaptive beamforming (BF) is essential when mmwave bands are utilized for mobile communications, where it is important that the channel experienced when BF is applied is as similar as possible to the estimated channel. This work investigates the similarity of the channel at different time-instants using estimates of auto-correlation functions for the instantaneous channel coefficients, based on 21.5 GHz measurements with a smartphone-like mock-up in different indoor corridor scenarios, with and without a user holding the mock-up. The correlation is found to be relatively independent of the location and orientation, with a reduced correlation with a person present. Further, BF is studied based on the 7-element handheld array with a 8.8-24.6 dB gain found for the 1st amplitude percentile obtained with ideal channel state information (CSI). Non-ideal CSI typically reduces both the correlation and the BF gain.

Multipath propagation can improve device-free localization (DFL). In this work, we therefore provide an overview of the required signal processing for multipath-enhanced device-free localization (MDFL) and introduce a possible sequential Bayesian approach. Furthermore, we demonstrate that low-cost ultra-wideband devices can be used for MDFL. Specifically, we use the Qorvo (DecaWave) DWM1000 module, for which we describe how to access the channel impulse response in detail. Based on a sparse network of ultra-wideband devices, we evaluate the localization performance of both DFL and MDFL for an indoor scenario. Thereby, MDFL is shown to clearly outperform DFL in terms of localization performance.

Location-awareness has playing an increasingly important role in wireless networks. Indoor radio frequency-based simultaneous localization and mapping (SLAM) can be enabled through ultra-wide bandwidth systems due to its ability to provide accurate channel information. In this paper, we provide a deep learning approach to improve the localization accuracy of users and reflection points based on a single-anchor ultra-wide bandwidth system in indoor complex environments. In the proposed approach, we propose a deep generative model to mitigate the distance and the angle-of-arrival estimation errors introduced by non-line-of-sight propagation. Instead of manually extracting features, we make full use of the amplitude and phase information in the channel impulse response to obtain more location-related information. Our work is validated by an indoor sufficient measurement campaign with self-built FCC-compliant ultra-wide bandwidth transceivers, and the results show that our approach outperforms conventional machine learning approaches in practical scenarios.

This paper deals with multipath-based positioning and tracking in off-body channels. An analysis of the effects introduced by the human body and the implications on positioning and tracking is presented based on channel measurements obtained in an indoor scenario. It shows the influence of the radio signal bandwidth on the human body induced field of view (FOV) and the number of multipath components (MPCs) detected and estimated by a deterministic maximum likelihood (ML) algorithm. A multipath-based positioning and tracking algorithm is proposed that associates these estimated MPC parameters with floor plan features and exploits a human body-dependent FOV function. The proposed algorithm is able to provide accurate position estimates even for an off-body radio channel in a multipath-prone environment with the signal bandwidth found to be a limiting factor.

A user-based navigation framework that exploits 5G signals is developed. The proposed framework exploits the "always on" 5G downlink signals simultaneously in a time-domain-based receiver to navigate a ground vehicle. To do so, a so-called ultimate synchronization signal (USS) is proposed to utilize the time-domain orthogonality of the orthogonal frequency division multiplexing (OFDM)-based 5G signals. This approach simplifies the complexity and enhances the performance of the 5G opportunistic framework. An experimental results was performed in a suburban environment to evaluate the proposed framework on a ground vehicle platform while sub-6 GHz 5G signals from two gNBs corresponding to two U.S. cellular providers. It is shown that over a trajectory of 2.17 km traversed in 230 seconds, the position root mean-squared error (RMSE) was 9.71 m compared to 14.93 m achieved using the state-of-the-art frequency-based 5G opportunistic navigation framework.

An antenna system composed of a single metasurface plate and a feed patch antenna is proposed. First, for inclusions of the metasurface plate, a double L-shaped metaatom is investigated, where the metaatom has inner and outer conducting arms. The change in the inner arm length creates a desired transmission phase for plane wave incidence on it. Next, the metasurface plate is placed above the feed patch antenna. As an example, a tilt beam of 60 degs is designed. The gain in a fixed direction of theta = 60 degs is approximately 18 dBi, which is approximately 11 dB higher than the gain of the patch antenna. The 3-dB gain drop bandwidth is approximately 12%. The VSWR at the feed point of the patch antenna is less than two.

Ultrathin metamaterial-inspired Huygens dipole antenna and rectenna arrays are presented for wireless power transfer (WPT) enabled IoT applications. The fundamental array element is the electrically small Huygens dipole antenna (HDA) that consists of two metamaterial-inspired structures: an Egyptian axe dipole (EAD) and a capacitively loaded loop (CLL). The EAD and CLL are designed on both sides of a single PCB substrate functioning as the in-phase and orthogonal electric and magnetic dipoles. A short-driven dipole close to the CLL excites the two radiators. Based on the single element HDA, an ultrathin, beam-steerable Huygens dipole antenna array (HDAA) with wide area coverage and small gain variation has been developed as a long distance WPT transmitter for battery-free applications. Experimental verifications of the simulated results are presented.

Space-time-coding (STC) digital metasurfaces have attracted great research interests due to their outstanding capabilities of manipulating electromagnetic (EM) waves and modulating information in various domains, which have been extensively studied to control the spatial and spectral distributions of EM waves. In this paper, we present a compact review of some new-architecture wireless communication systems based on the STC digital metasurfaces, which have the advantages of low cost, low complexity, low power consumption and high efficiency, and provide candidate technologies for future 6G wireless communication networks.

In this paper, a high-efficiency multifunctional full-space metasurface is proposed to independently control the reflection and transmission wavefront. As a proof of concept, a broadband reflect-transmit-array antenna with bidirectional high-gain beams is designed in the 5G millimeter-wave band around 26.8 GHz. The finally assembled antenna achieves 1-dB gain bandwidths of 21.2% (16.2%) and 3-dB axial ratio bandwidths of 35.5% (36.5%) for reflectarray (transmitarray) operations. Moreover, a total aperture efficiency of 55.8% is realized by considering the two radiation operations. The proposed reflect-transmit-array antenna with the advantages of broad bandwidth, high aperture efficiency, and high polarization purity maybe a promising candidate for bidirectional wireless communication applications.

We present a rigorous analytical model utilized to design highly-sparse antenna arrays, taking advantage of the recent concept of metagratings (MGs). The proposed semianalytical methodology, avoiding full-wave optimization, enables replacement of the generally-large number of active radiating elements with passive capacitively-loaded wires (meta-atoms), without sacrificing array directivity. Contrary to common techniques to dilute arrays, relying mostly on optimization of active element distribution and excitation, our modular solution utilizes a standard array configuration with linearly-phased elements; grating-lobe suppression is achieved by proper engineering of the passive MG, harnessing Floquet-Bloch formalism to control power partition into diffraction orders. To facilitate dramatic dilution and comply with printed-circuit-board (PCB) design requirements, we extend our previous work, enabling inclusion of multiple meta-atoms per period within a multilayered dielectric substrate. This concept, verified via full-wave simulations, is expected to facilitate the development of low-cost, planar, low-loss, and highly-directive antenna systems for future cellular and satellite communication.

Design of modulated metasurface antennas has been recently treated as an inverse problem stemming from the discretization of an EFIE equation. Fourier-Bessel basis functions have been used for representing the currents and the IBC. We explore a similar formulation of synthesis taking advantage of the use of a set of quasi-orthogonal sub-domain Gaussian-Ring basis functions. Representation of the MTS equivalent impedance in terms of this base allows to invert the EFIE problem and, therefore, to directly define the boundary conditions suitable to generate a rather arbitrary radiation pattern. The technique combines the possibility of directly designing the aperture IBCs with advantages coming from GRBF adoption. Such a base offers the power of sub-domain functions spatial resolution and the possibility to define the unknown impedance on a customary interval. Furthermore, the analytical expression of the basis functions allows for quick closed or semi-closed form evaluation of matrices in EFIE inversion procedure.

The method of the equivalent currents for antenna diagnostics has been widely demonstrated over the years on a large set of measured data. Its key advantage is to provide a complete 3D representation of the antenna by a direct post processing, without any additional testing, like probing. Recently, the method has been equipped by a technique based on a Nested Skeletonization Scheme (NSS) for post processing of very large antennas. In a previous investigation the post-processing with NSS has been applied to a prototype of an array antenna. Only a portion of the array geometry has been considered in the investigation for the limitation imposed by RAM constraint.

In this paper we will show a new technique that enhances the NSS method for processing of large problems and that makes possible a complete diagnostics investigation where previously this was not feasible.

Antenna measurements using an extrapolation range have been used for accurate far-field gain calibrations since the 1970s. It is still considered one of the most accurate methods for obtaining the absolute far-field gain of an antenna. The method is based on curve fitting the scalar antenna responses to the generalized transmission equation, which is in the form of a polynomial equation. It is much more common today to use vector network analyzers in an extrapolation range. The vector data provides experimentalists additional processing tools to further improve measurement accuracy and reduce effects from extraneous reflections in the chamber. In this paper, we explore the use of angular spectrum filtering for removing chamber multipath effects from the response data. Specifically, we demonstrate the benefits by applying the technique on a set of measurement data obtained in a 30'x30'x70' fully anechoic extrapolation range.

Prediction of chamber reflectivity levels based on the geometry-optics based ray-tracing method by considering only the specular modes is accurate at microwave frequencies but fails at mm-wave frequencies. Previous research laid out methods on the extraction of higher-order modal reflectivity of the anechoic absorber at mm-wave frequencies. The higher-order modal scattering were translated to chamber modelling and a cumulative reflectivity heat-map was generated. This paper explore an alternate approach based on Design of Experiments analysis to reduce the simulation time while maintaining the simulation accuracy. In addition, another approach based on PML boundary condition and plane-wave excitation is explored to overcome the 100-mode limit of the Floquet based model results.

The use of active antenna arrays in mobile radio applications such as 5G New Radio has made it necessary to define new metrics to evaluate these antenna systems. The guidelines in the mobile radio network are regulated by 3GPP and require conformity testing. The legal rules, which serve for the protection of persons against electromagnetic fields, have to be fulfilled as part of the approval procedure for a base station. In this paper, requirements are presented regarding the definition of radiation patterns. It also shows a measurement method for measuring the envelope curve, which is the basis for calculating the electromagnetic field exposure in the approval procedure in Germany. Applying this method, the measurement results of a millimeter-wave antenna are presented.

The role of field correlations in the intrinsic measurement uncertainty in reverberation chambers (RC) is a topic of great interest for many electromagnetic compatibility as well as over-the-air measurement techniques. This paper investigates the applicability of an exponential correlation model to measured electric field intensities in a RC under different loading conditions. The exponential model allows for a robust estimation of the average correlation in measured data, which is a key parameter for quantifying measurement uncertainty.

This paper revisits the formalisms of coordinate system and rotation transformations encountered in diverse antenna analysis and measurement scenarios in a unified fashion. Both Eulerian angles and quaternion constructions are applied and relevant details are presented. The advantages and disadvantages of both constructions are discussed, and appropriate formulas are developed to demonstrate how these two formalisms could be interrelated.

This paper discusses the limited test volume of FR2 MIMO OTA test systems according to 3GPP specifications. The current FR2 MIMO OTA test system supports a 20 cm diameter UE size. However, 5G services are expected to include larger devices, such as tablets and small-scale monitors, as well. We show that the best way to improve the performance of the FR2 MIMO OTA system is to increase the chamber size to support a 1.75m range length instead of the current 0.75m range length. We also discuss the error factors inside the test volume, showing how the boundary of the test volume dominates the error.

The impact of selecting a BS array with a two different polarization options are compared using several different performance characteristics. A V&H polarized array utilizing Plus (+) elements is compared to an array with slant 45° (X) elements using standardized models to evaluate potential differences in PDP, Autocorrelation, eigenvalues, and Capacity estimates. Comparisons are made and discussed.

From mid of 2020 to mid of 2021, the 3G mobile radio network in Germany was gradually replaced by the successor technologies 4G and 5G. Therefore, dynamic spectrum sharing (DSS) was introduced in the 2100 MHz band, which allows a parallel operation of 4G and 5G. There is an increasing need of public information with regard to a possible change in human RF exposure associated with 5G and DSS. Hence, investigations were carried out to study the instantaneous and maximal exposure of persons to base stations in the 2100 MHz band. Our study shows, that the instantaneous exposure has remained comparable before and after the introduction of 4G/5G with DSS. Regarding the maximal RF exposure, code-selective measurements of 3G and 4G with DSS show no significant change in exposure. To analyze the maximal exposure to 5G with DSS, code-selective measurements have been applied for the first time and compared with the 4G exposure in the same band. The results show no significant difference in maximal exposure between 4G and 5G. Furthermore, the need of code-selective measurements in comparison with the frequency-selective method for 5G is demonstrated if different parts of the electromagnetic field that contribute to exposure have to be assigned to selected base stations.

This paper presents a sub-array internal element calibration method using linear matrix inversion method. Multi-probe is employed to detect the E-field distribution of the sub-array under test in the near field. A transmission matrix between the sub-array and probes is built. The key point of this method is getting low condition number transmission matrix. Furthermore, optimization strategy based on genetic algorithm is introduced to obtain more stable matrices. Simulation results show only 4 probes are needed for a 4-element array testing. Finally, a 4-element sub-array composed of rectangular waveguide antennas operating at 3.5 GHz was measured to validate the effectiveness of the proposed method, and the results show a high accuracy - the error between the proposed method and the reference test is less than ±0.2dB, ±2°.

This paper considers mobile network testing for 5G NR (both sub-6GHz and millimeter wave frequency bands) with a passive RF receiver. Methods for the measurement of network coverage, network synchronization, channel impulse response, and the strength of the electromagnetic field with a code selective procedure are proposed and implemented. An approach for automatic channel detection is presented in order to find the relevant carrier frequencies for 5G mobile network testing in networks with an unknown configuration. Finally, the proposed methods are applied for deployed 5G networks, demonstrating the effectiveness of the equipment.

Fast array diagnosis method is of great importance for ensuring reliable array performances in the fifth generation(5G)communication systems. In this paper, a fast array diagnosis method is presented for antenna arrays composed of several subarrays. The objective is to detect the failures based on the measured complex array signals in short measurement distance. A single probe is required to record the array response in the near-field of the array. All the array elements are excited simultaneously, and only phase shift states of 0 and 180 degree are required in the measurements. For a base station(BS)antenna array with N subarrays, N+1 measurements are required, resulting in a fast diagnosis process. Finally, the proposed method was validated in an antenna array composed of 4 subarrays with 3 antenna elements in each subarray and successful diagnosis results (both for the faulty subarray and faulty single antenna element in subarray cases) can be observed.

Deployment of the fifth-generation (5G) mobile communications at the millimeter-wave (mmWave) part of the electromagnetic spectrum comes with concerns related to exposure of the human to electromagnetic field (EMF). The irradiation of the human body from phased antenna arrays, integrated into handsets operating at mmWave frequencies, is evaluated in terms of power density (PD). This paper presents a study on the local incident power density (IPD) on a surface made of vacuum and having the shape of the specific anthropomorphic mannequin (SAM) head phantom. The employed array consists of four off-ground half-wavelength dipoles. Two different orientations of the mobile terminal with respect to the phantom - cheek and tilt position are studied, as the goal is to find test exclusion possibilities. According to the results, the lower exposure in the tilt position (regardless of the frequency, inter-element spacing, and array excitation) allows tests for this handset orientation to be omitted.

Virtual drive testing (VDT) with measured or ray tracing (RT) simulated channels requires the simplification of the channel to match the hardware specification of radio channel emulators. That is, reduction of the number of multipath components (MPC)s and adjustment of the arbitrary delays of the MPCs to the sampling grid of the radio channel emulator. In this paper, a fractional delay (FD) filter approximated by a general least square (GLS) finite impulse response (FIR) filter is used for band-limited interpolation to align the delay of the MPCs to the sampling grid of the radio channel emulator. A dominant power selection strategy is then employed to reduce the taps to match a given hardware specification. The GLS FIR method is shown to have superior performance in preservation of the channel frequency response (CFR) compared to rounding delays to the nearest integer multiple of the sampling time.

Millimeter wave (mmWave) technology is one of the key technologies introduced in 5G new radio(NR). Abundance of spectrum resource allows the mmWave 5G NR to achieve higher rates, greater capacity and lower latency. Performance test is a powerful means to help develop mmWave technology. Particularly, over-the-air (OTA) test is the only practical method for mmWave technology due to the lack of accessible antenna port on mmWave devices. The Third Generation Partnership Project (3GPP) has started the studies on mmWave MIMO OTA performance test methodology for which channel model validation is crucial. This paper investigates the impact of test antenna pattern under near-field condition on mmWave channel model validation. Simulation shows that different models have different requirements for the test antennas of which omnidirectional antennas are not always needed.

Fifth Generation (5G) technology is about to set its global footprint. Its success relies heavily on the standardization process, which is rapidly progressing to specify verification metrics and test methodologies for 5G New Radio (NR) device certifications. For this purpose, three-dimensional (3D) multi-probe anechoic chamber (MPAC) has been selected as a reliable reference solution for creating an accurate test environment. This paper reports first ever FR2 MIMO over-the-air (OTA) channel models validation measurements according to 3GPP specified verification procedure. The evaluated validation metrics include power-delay profile (PDP) and power-angular spectrum (PAS) similarity percentage (PSP). The measurement results closely follow the simulated and theoretical references, thereby demonstrating the feasibility of FR2 MIMO OTA channel models validation procedure adopted by 3rd Generation Partnership Project (3GPP).

This paper investigates measurement-based omni-directional millimeter-wave propagation characteristics for an indoor corridor environment. The omnidirectional characteristics were obtained with actual omnidirectional antenna measurements both at TX and RX, and not by synthesizing directional antenna measurements. With wideband sounding at 28, 38, 71 and 82 GHz, we analyzed path loss, shadow fading, excess loss and delay spread characteristics. In the path loss and the excess loss analyses, evident differences between the LOS and the NLOS were observed due to the waveguide effects. In the excess loss and the delay spread analyses, gaps were observed between the relative lower mmWave frequencies (28 and 38 GHz) and the upper frequencies (71 and 82 GHz).

This paper presents the dimensionality reduction of a propagation channel dataset created through a measurement campaign. The scenario knowledge is essential for the signal processing prior to the transmission and the application of these techniques allows a quick scenario differentiation. The measurement campaign, which has been performed in the SWAT research group's facilities at the University of Granada, includes propagation channels from three different scenarios: anechoic, reverberation and indoor. t-SNE, a Machine Learning technique that performs a non-linear dimensionality reduction, has been applied to the propagation channels. The results show the separability of the three scenarios in a low-dimensional space for an optimal election of the t-SNE hyperparameters. The most relevant hyperparameters in the performance of the technique are the distance metric and the perplexity.

The performance of indoor wireless systems depends on the deployment scenario, so proper parameterization and planning of the local area network (LAN) are crucial, in particular in the millimeter wave band which suffers from blockage. Two of the key performance indicators for wireless LANs are the packet delay and the end-to-end latency, which are related to the amount of redundancy added at the PHY and MAC layers, aimed to compensate the dispersive effect of the radio channel, usually represented by the root mean square delay spread (RMS-DS). This paper proposes a model that helps to predict RMS-DS in 60 GHz band based on room's geometry and compares the results with the ITU model. The work is based on measurements and results previously presented in the literature, especially focuses on offices and conference rooms.

A satellite beacon receiver is designed for research and educational purposes. To provide data to investigate possible weather induced scattering processes, a complex valued dual branch architecture is chosen, operating in the Q-band. The construction is based on mostly readily available components and instruments at Aalborg University radio laboratory. The paper describes the beacon receiver and its features.

Outdoor-to-indoor propagation path-loss measurements have been carried out at 27 and 38 GHz, two of the frequencies allocated for 5G networks, for two different buildings: an office glass, steel and concrete building and a brick-wall residential house. The outdoor station has been mounted on a drone in order to have more placement flexibility and reach the desired height above ground without the use of a crane truck. Overall outdoor-to-indoor loss seems to depend primarily on the window surface and on the construction material. While loss is higher at 38GHz with respect to 27 GHz for the office building, brick-walls of the residential house appear to be less frequency selective.

This paper describes the measurement setup for the proliferation of the vehicular communication systems in operating cars. The setup builds on a communication sniffer which detects cooperative awareness messages broadcast from ETSI ITS-G5 systems, decodes them and records the public information in these messages. The experimental characterization of the setup in an outdoor scenario is presented in order to verify the sniffer's performance with respect to transmit power and communication range. The setup is deployed for measurements on a busy road with slow moving traffic in the center of the city of Linz, Austria. The number of active users as well as their transmit power, duration of the transmission and packet length have been recorded.

There is a frequent requirement in spectrum sharing studies (e.g. in relation to frequency assignment for 5G systems) to assess the basic transmission loss on short (typically less than 1 km) outdoor paths in a variety of environments. In most sharing studies, it is required that the results of the modelling are generic (i.e. no site specific inputs to the model are necessary) and are presented in statistical terms (typically path loss not exceeded for a given probability). A useful model must also be suitable for computer implementation, often within a Monte Carlo framework. Many existing models are deterministic in the sense that they apply to specific geometries or environments which makes it impossible to apply such models in the general case where statistics covering all path geometries are required. This paper proposes a new, unambiguous, method for the prediction of the statistics of basic transmission loss in such cases.

The design of a periodic leaky-wave antenna for angle-of-arrival (AoA) estimation is presented. Thanks to multiple radiating space harmonics, a multibeam operation is achieved in order to scan a large angular range with a limited fractional frequency bandwidth. The matching and radiation efficiency issues raised by the large spatial period involved with multibeam operation is addressed by using a dedicated unit-cell to control both the leakage constant and the Bloch impedance. Simulations confirm that a MUSIC processing enables the system to perform AoA estimation without ambiguity among the multiple beams. This allows for AoA estimation over the 180°-angular range with a bandwidth of only 3.7% at 27 GHz.

In this paper, we propose a detailed generic reference plane model for performance evaluation and system validation of radio channel sounders. It allows to abstractly describe a broad variety of channel sounder implementations and architectures in a common framework, thus facilitating systematic evaluations and comparisons. To illustrate the utility of the concept, we present the mapping of two practical channel sounder realizations - one time domain and one frequency domain - to the model, along with selected performance metrics defined on its reference planes. For the two presented channel sounders, we give measurement examples for these metrics.

In this paper, we discuss some challenges for 5G-and-beyond communications systems based on our measurements conducted with millimeter-wave (mmWave) channel sounders. One study analyzes path loss at 28 GHz vs. 83 GHz and in line-of-sight conditions vs. non-line-of-sight conditions and finds it to depend much more heavily on the latter than the former. A significant factor of path loss is penetration loss; in fact, another study focuses on obstructions that are typical in wireless environments: building walls, human bodies, and trees. Finally, in addition to investigating how power is distributed over distance through path loss, we also investigate how power is distributed over delay and angle per distance, otherwise referred to as channel dispersion. In particular, we discuss the importance of diffuse multipath to the total received power at mmWave and the foregone conclusion of wide-sense stationarity, which we show will often not apply to mmWave small-scale fading.

In this paper, a method of designing antennas by avoiding crossing between the modes is presented. This is aimed at enhancing antenna bandwidth using ground fragmentation techniques based on the characteristic modes analysis (CMA) approach. A compact and flexible Saxophone antenna and a conventional rectangular microstrip antenna both dimensioned at 30 × 30 mm 2 (0.66λg × 0.66λg) are designed to operate at 5.8 GHz to validate the proposed method. The proposed saxophone structure with a full ground enhances the bandwidth up to 170 MHz (2.97%) relative to the conventional antenna. This is then improved up to 890 MHz (14.67%) and 794 MHz (13.58%) when integrated with a fragmented and a partial ground plane, respectively. In comparison, the conventional antenna exhibited a bandwidth of 360 MHz (6.38%) and 410 MHz (7.25%) for these cases. Modeling is performed using FEKO software based on two approaches: the method of moments (MoM) and CMA. Results show a satisfactory agreement of the predicted resonant frequencies from simulations and measurements.

In agricultural applications, it is becoming ever more important to be able to send sensor data in an energy-efficient way, possibly from each plant. This study investigates the possibility to excite a plant leaf using an Antenna Booster to enhance antenna performance. A PCB including a Matching Network is designed to accommodate the Antenna Booster. This PCB is placed in a simulation environment on material emulating the electrical properties of a plant. It is shown that the Antenna Booster uses the PCB and the leaf it is placed upon to radiate. The simulations show that it is possible to increase the radiation efficiency of the antenna structure from 9.6% up to 15% at a frequency of approximately 2 GHz by attaching the Antenna Booster to a leaf-like plane, and that using the leaf thus should be considered in the Internet of Plants (IoP).

In this paper, a highly miniaturized folded slot-based antenna is presented for internet of things (IoT) applications. It consists of meandered slot with folded structure along with varactor diode loading. Miniaturization is obtained using a unique combination of meandered slot with folded structure that is reactively loaded with varactor diode. The antenna exhibits dual-bands operation covering frequency bands from 730∼965 MHZ and 1250∼1940 MHz. A single varactor diode is used to obtain a continuous frequency sweep over both bands. The proposed antenna is best suited for next generation 5G IoT applications. The proposed antenna design has a total board dimensions of 27×27 mm 2 .

The growth of the Internet of Things (IoT) requires that a large number of devices need wireless connectivity. For this reason, a simple and fast method capable of designing multiband antenna systems, utilizing a very simple antenna element is proposed. In this method the antenna is seen as an impedance box where a multiband matching network with lumped components is the one that fixes the number of frequency bands. The multiband matching network was designed in Optenni Lab based on the measured antenna input impedance and the EM-simulated radiation efficiency. To validate the procedure, a multiband antenna system operating at 824MHz-960MMHz and 1710-2690MHz is implemented. The matching network has been obtained through a fully automated process without human intervention and without any type of adjustments. This enables the design of multiband antenna systems in a quick, easy, and systematic way.

Antenna design, starting from scratch, using full wave analysis software can become a very time consuming task. Using analytical (approximate) antenna models, especially at the initial stage, can reduce the overall design time considerably, as is shown in this paper. To help antenna designers, a list of common antenna types and the accompanying models is given. Two of the models have not been published, in the current form, before.

De-embedding antennas from the channel using Spherical Wave Functions (SWF) is a useful method to reduce the numerical effort in the simulation of wearable antennas. In this paper an analytical solution to the De-embedding problem is presented in form of surface integrals. This new integral solution is helpful on a theoretical level to derive insights and is also well suited for implementation in Finite Difference Time Domain (FDTD) numerical software. The spherical wave function coefficients are calculated directly from near-field values. Furthermore, the presence of a near-field scatterer in the de-embedding problem is discussed on a theoretical level based on the Huygens Equivalence Theorem. This makes it possible to exploit the degrees of freedom in such a way that it is sufficient to only use out-going spherical wave functions and still obtain correct results.

This article presents a multi-band antenna system covering LP-WAN, GNSS and WiFi bands. The 868MHz and 1575MHz bands have a right-hand circular polarization with a wide aperture beamwidth. The 2400MHz band provides an omnidirectional pattern with linear polarization. The complete system is built using two FR4 substrates connected through vertical wires. The overall system has a size of 727212mm. A total efficiency higher than -3dB is measured for the three bands.

The paper presents a novel compact wearable harmonic transponder, composed of a dual-band patch-type antenna loaded by an HSMS-2820 Schottky diode, operated at 869 MHz and 1 734 MHz frequencies. The antenna itself is optimized for a minimum ground plate size. The transponder performance was evaluated both in free space and when attached to a human muscle phantom. The total harmonic transponder conversion loss is 6.2 dB for an excitation power of −25 dBm at the antenna-diode interface, outperforming state-of-the art solutions. The measured reading distances are 9.0 m and 8.8 m for EIRP = 20 dBm when the transponder is placed in free space and on the human body, respectively. As a means of machine-to-person communication, the transponder is suitable for Internet-of-Things concept.

In this paper, a novel chip antenna and its function in wireless connectivity are presented for Bluetooth(BLT) earphones. The chip antenna is a CRLH-metamaterial so compact as the size of 4.9×13.0×2.0 mm3 that when it is mounted on the PCB, it can sit in the enclosure of the BLT earphone. This setting does not degrade the resonance of the proposed antenna. As two earphones in a pair are demanded to communicate with each other, one shares an RF signal with the other and they take turns as the master and slave. The received signal sensing indicator(RSSI) is observed for that pair of the chip antenna-mounted earphones. Electromagnetic simulation of the antenna is done and verified by fabrication and measurement. Especially, a good RSSI is obtained as -67.5 dBm, larger by 50 dB than the threshold.

In this paper, the design of a 3D printed Dielectric resonator for S-Band application is studied. A dual-band structure is targeted in order to support uplink and downlink satellite communication. A partial filling of some specific part of the DRA is used to optimize the antenna input impedance. The designed DRA exhibit a compact dimension of 0.250.250.1 wavelength with a 5dBi realized gain.

Microwave imaging for breast cancer detection has attracted growing global attention with a small number of prototypes advancing to the clinical trial stage. This investigation aims to provide an overview of MammoWave, a novel microwave-based imaging system for breast lesion detection and to assess its introduction into the clinical routine and its potential role in future breast screening programs. As a key focus of this work, we will describe in detail the various aspects of the clinical protocol procedure that has enabled us to perform a successful clinical trial. Obtained preliminary results indicate the ability of our device to distinguish breasts with no radiological finding and those with radiological findings, with a sensitivity of 89.6%.

A mobile electromagnetic tomography brain scanner prototype was developed, with the aim of the first mobile bed-side application of the technology for human brain imaging in a clinical setting. The usability and safety of the scanner was ensured to fulfill the requirements for clinical study operation. The mobile electromagnetic scanner was successfully put through its first pilot feasibility clinical study on healthy volunteers and real stroke subjects. The goal was to prove safety and feasibility of the technology for operation in the clinical setting, as well as gathering the first indication of its ability to detect and differentiated between ischemic and hemorrhagic strokes. The outcome is a significant step towards a safe and clinically viable EMT solution, where the scanner was proved to be safe and usable in healthy volunteers and real patients and first indications of its ability to detect brain pathology in stroke patients.

Colorectal cancer is one of the most common diagnosed tumors. The cancer is prevented with an early detection of polyps that may appear on the colon wall. This paper presents a microwave system for colonoscopy application. The goal is to improve the polyp detection rate by combining microwave information with the current optical video. It presents the main challenges on the prototype design, facing regulatory, industrialization and clinical acceptance requirements. Finally, the system is validated with ex vivo measurements to analyze its performance.

The solution of inverse scattering problem arising in microwave imaging generally requires the knowledge of the incident field distribution inside the imaging domain. This task can be accomplished by sampling the whole imaging domain, but resulting into an inconvenient strategy. Alternatively, the incident field can be collected on the measurement domain only, by subsequently retrieving the required field distribution. In this contribution, a two-step phaseless strategy for the prediction of the incident field distribution is presented. Starting from the intensity knowledge of the incident field on the measurement domain, the corresponding phase is retrieved by applying a Spatial Domain Indirect Holography Technique. The retrieved complex incident field is then exploited within a Modal Expansion formulation for the incident field reconstruction inside the imaging domain. The validity of this combined approach is tested within a phaseless inverse scattering strategy, where intensity-only data relative to the total field are assumed to be sampled. The effectiveness of the proposed solution is demonstrated through validation on a breast imaging scenario.

We develop a battery-free communication system for wireless-capsule endoscopes with video streaming at a rate of up to 15 Mbps. We apply our innovative approach using backscatter for implants- a RADAR approach that remotely reads the information from the deep implants, such as the video capsule endoscope. We use the 5G deployed network with edge computing and slicing to transmit the video data from the capsule to a high-performance computing platform in a secure way with guaranteed end-to-end latency to perform polyp detection and localization. This way, the energy-intensive inference using deep learning neural networks for polyp detection and localization can be performed in the edge where control signals are sent back to the pill to increase the spatial and temporal resolution of the video, to obtain high-quality images for further analysis. The paper provides a system-level description, with a demonstrated setup for the capsule data streaming to the network.

This paper presents the ground test and flight test campaign of the electronically steerable SATCOM aero antenna (E2S2A2) developed under Clean sky 2 project (717164-E2S2A2-H2020-CS2-CFP02-2015-01). The antenna is installed in an AIRBUS 295 prototype aircraft completely embedded without modifying the aerodynamic shape of the aircraft. Ground test and Flight test campaigns are planned and carried out in order to demonstrate connectivity under specific satellite coverage.

This paper describes the conformal and structural integration of a Ku-band phased array antenna in the fuselage of an aircraft. A novel fuselage panel with an orthogrid stiffened structure has been developed. The cells of the orthogrid structure are used for the embedding of the Ku-band antenna tiles.

A very high-gain continuous transverse stub (CTS) array targeting K/Ka band for SatCom applications is presented. The CTS array is fed by a tapered corporate feeding network (CFN) to reduce its sidelobe level to -20 dB over the full intended band (17 GHz - 31 GHz). A new pillbox coupler is introduced to illuminate the CTS array, with a reflection coefficient better than -10 dB over a 200% relative bandwidth. Multiple sources in the focal plane of the pillbox coupler allows steering of the antenna main beam in elevation up to ±65°. The fabrication technology used is hybrid. The pillbox coupler is designed by classical milling while the rest of the antenna is in multi-layer printed circuit board (PCB) technology. The size of the antenna is 62.2×62.2×2.2 λ_0^3, where λ_0 is the free space wavelength at 31 GHz. The minimum calculated gain is 38.5 dBi at 17 GHz.

A simultaneous X-band and wide-band Ka-band horn is designed for reflector antenna satellite communication applications. The theoretical performance of a 2.4m offset parabolic reflector, a 13.5m shaped Cassegrain reflector and a compact 1.3m dual reflector antenna are calculated as a proof of concept.

The design of a dual-polarized broadband array that simultaneously covers the Ku- and Ka- satellite communication transmit bands is presented. The array element is a connected slot backed by a ground plane and loaded with artificial dielectric layers. The design includes the detailed feeding structure for the two polarizations and accounts for realistic manufacturing constraints in the definition of the layer stack-up. A conical scan volume of up to 60 degrees is achieved with active voltage standing wave ratio (VSWR) below 2 in the Ku-band and below 3 in the Ka-band. An efficient numerical method to analyze the finite-by-finite array is also presented and can be used to estimate the edge effects.

The recent developments of dual-circularly-polarized (dual-CP) reflect-arrays (RAs) at microwave and millimeter-wave frequencies are reported. In the first part, dual-CP RAs with a wide operational bandwidth are described through several demonstrating examples. Two strategies are employed - one utilizing only Berry phase with two functional layers and the other exploiting both dynamic and Berry phases for dual-CP beamforming with a single functional layer. In the second part, by incorporating shared-aperture techniques into the RA cell alignment, dual-band dual-CP RA cell designs are described, which have four degrees of freedom in terms of reflective phase control. The designs are numerically validated by diffraction analysis of a linear gradient array of dual-band dual-CP RA cells, exhibiting reflective beam bending with both simultaneous polarization and frequency diversities.

In this overview paper we summarize our results regarding the problem of extending the angular scan range of antenna arrays using Huygens' lens-like metasurfaces. Existing theory of scan enhancement using lenses is summarized, where various devices are discussed. This includes the single-lens far-field enhancer, the single-lens near-field enhancer and finally the two-lens near-field enhancer. An important addition to existing work is that physical metasurface structures are full-field simulated. Extremely close agreement between simulated and theoretical results is observed despite non-idealities such as losses which are present in the simulations.

In this paper, different configurations of multi-faceted reflectarrays for small satellite platforms are evaluated. The reflectarrays are designed in a SATCOM band to generate a directive beam in dual-linear polarization. The performance and physical characteristics of both antennas are compared with a flat reflectarray of a similar aperture. The proposed multi-faceted configurations improve the in-band performance antenna without an increase in the complexity of manufacture, satellite storage, and in-orbit deployment.

This contribution presents preliminary results of a reflectarray antenna to generate a multi-spot coverage from a LEO satellite for 5G and Beyond-5G communications. The reflectarray is proposed to generate the complete multi-spot coverage at 18.2 GHz for the user's downlink. The phase distributions on the reflectarray surface have been optimized to broaden the beams at the same time as reducing the distortion of the beams at the edge of the coverage. The antenna performance of a standard reflectarray (with a conventional phase distribution to focus pencil beams) and the proposed reflectarray have been compared by simulated results. The simulations show that the proposed reflectarray can generate a continuous coverage of 36 beams with an End-Of-Coverage level of 26 dBi.

In this work, preliminary results on the design of a dielectric transmitarray (TA) antenna are presented. The unit-cell consists in two circular cylinders located on the two sides of a thin square slab, with size 0.3λ at the central frequency, realized with the same dielectric material of the cylinders. The amplitude and phase of the transmission coefficient are controlled varying the diameter of the cylinders, while their height is kept constant. In order to minimize the unit-cell thickness, but at the same time assuming that 3D printing techniques will be used for the TA manufacturing, a dielectric material with εr=10 is considered. The results obtained from the simulation of a transmitarray working in Ka-band with size 15λx15λ are presented and discussed.

In this paper, we present an approach to realize wideband, 1-bit (2-bit), reflectarray unit cells using only one (three) single-pole-single-throw switch(es). The proposed reflectarray unit cells consist of an antenna and a reflecting circuit with a switchable phase shift response that is controlled using PIN diodes. The reflecting circuit entirely reflects the incident wave received by the antenna with a phase shift that can be adjusted electronically by controlling the PIN diodes. The proposed reflectarray unit cells offer two primary improvements over the state-of-the-art in electronically tunable reflectarray antenna designs: significant bandwidth enhancement; and reduced implementation complexity. As a proof-of-concept, we designed reflectarray unit cells with 1-bit and 2-bit phase quantization. Our approach enabled us to achieve wide bandwidths of 78% and 50% for the 1-bit and 2-bit reflectarray unit cells, respectively.

We present a metasurface based planar deflector that can be used to realize a low-profile antenna with mechanical beam steering capability in a wide angular range, within a large bandwidth. The deflector exploits a Pancharatnam-Berry phase effect to steer the beam and allows to maintain low side lobe levels within the whole antenna field of view. Numerical results are provided as support to the discussion. The device has been conceived for next generation satcom communication in the Ka-band from user terminals on board of moving platforms.

The aim of this paper is to present the design of a Ku band, active multibeam antenna working both in transmission and reception. The dual band antenna system is constituted by an active discrete lens magnified by two confocal paraboloidal reflectors. The novelty and the main challenging aspects are associated to the combined transmit and receive functionalities of the active discrete lens. In order to guaranty the dual band operation, an innovative RF building block chain working in dual polarizations has been introduced. In addition, the magnifying reflector system permits to mimic an active array of larger dimensions.

We propose here a 40×40-element shared-aperture dual-band dual linearly-polarized transmitarray with 1-bit phase resolution and fixed beam at Ka-band. The design is based on a stacked approach where the unit-cell size is compact and is equal to only 0.48×l0 and 0.32×l0 at 29 GHz and 19 GHz, respectively. The beam-scanning performances of this array are compared to those of an array with the same number of elements and same illumination but comprising unit-cells based on the interleaving approach (lattice size of 0.72×l0 and 0.47×l0, respectively). The shared-aperture unit-cells include four printed U-slotted patch antennas and a connecting metallized via; the desired 180° phase shift is obtained by rotating one of the patches around its corresponding via. Our simulation results demonstrate that the transmitarray based on the stacked approach exhibits excellent beam scanning performance up to ±70°. A prototype pointing at broadside is optimized and fabricated to validate the numerical simulations

A technique for the extraction of the polarizability of a particle or equivalent sheet impedance of printed circuit elements in aperiodic metasurface environments is presented. The technique does not rely on local periodic assumptions that are commonly made in metasurface sheet impedance extraction techniques. Instead, the local electric field and induced surface current on each of the homogenized sheet impedance elements in the aperiodic array is extracted from a solved linear system representing the electromagnetics problem. The ratio of local electric field to induced surface current density defines the element impedance in the true aperiodic environment. This impedance is used to find a printed circuit element which generates the same current when excited by the local electric field. Geometrical parameters are varied until agreement between the homogenized sheet impedance and the printed circuit element is observed. An example of an aperiodic 10-element metasurface is provided.

An equivalent circuit for the unit cell of bi-periodic surfaces is proposed. The equivalent circuit is general and simple. It is based on the decomposition of the eigenmodes of the structure and it takes into account the polarization of the incident wave. It consists of the interconnection of two different admittances and two transformers. The model of a unit cell composed of three parallel dipoles is extracted. The transformer models the rotation of the dipoles, while the admittances model their resonances. This equivalent circuit provides physical insight and, at the same time, it separates the contribution of the rotation from the resonances. The model is able to replicate the simulation result with great accuracy.

This work presents the methodology of design and the characteristics of an active, three layer unit cell embedded in a radome. The structure covers a phase range of 330 o with a transmission magnitude better than -3 dB. The design of the proposed active unit cell utilizes 2-port network theory to estimate the port impedance of each layer and the transmission coefficient of the complete structure.

This paper presents a theoretical study of diagonal-symmetric metasurfaces based on very simple transmission-line models in order to achieve wideband polarization converters. The approach profits from the decomposition of the incident-field vector in field components directed along the diagonal-axis, decoupling the problem into two different, individual and independent subproblems. This issue reduces considerably the complexity of the problem, and allows for a better understanding of the physical insight of the structures. Practical examples of wideband rotators/circular polarizers based on very simple metasurface-cells are implemented with the aim of supporting the theoretical conclusions. Experimental prototypes have successfully been manufactured and will soon be tested.

A partially reflective surface (PRS) antenna is a low-cost high gain antenna, which is often classified by the capacitive or inductive nature of the PRS. It has been shown that, for a given reflection magnitude, capacitive PRS facilitates a larger antenna gain than inductive PRS, based on leaky-wave model and practical design examples. In this paper, we extend the classical ray-tracing approach to derive analytically that the superior gain is primarily due to the greater height of the capacitive PRS from the ground plane, which leads to a smaller phase delay and a more uniform magnitude distribution across the PRS. To verify the analytical study, the simulated phase and magnitude distributions of a capacitive and an inductive PRS antenna are produced and shown to agree with the predicted trends of the phase and magnitudes distributions from ray-tracing.

When considering near couplings, the design and optimization of metasurfaces would consume huge time and memory costs. Deep neural networks provide unprecedented computational efficiency and accuracy for solving complex electromagnetic calculation problems. In this paper, two deep neural networks (DNN) are designed to solve the fast design and optimization problems of surface-enhanced Raman scattering (SERS) and focusing with metasurface respectively. The numerical calculation results prove the effectiveness of the work in this paper.

Metantennas have triggered enormous opportunities in antenna designs but along with arduous challenges. The views and overviews of critical issues, such as ohmic losses, of metamaterials and metasurfaces-based antenna designs at microwave bands are shared. The opportunities and challenges in future metantenna research and applications are predicted and proposed hopefully to pave future ways to enhance performance and introduce more functions of microwave antennas.

In this paper, three compact dual-polarized millimeter-wave antenna array designs for 5G mobile handset are presented, including an end-fire antenna array, a broadside antenna array and a tilted-beam antenna array. The environmental effects are also considered in the antenna designs. In the validation, these three designed antenna arrays can effectively cover 5G N257 (26.5 GHz -29.5 GHz) and N258 (24.25 GHz -27.5 GHz) frequency bands for both polarizations with different radiation directions. Especially, for the tiltedbeam antenna array, the beams of dual polarization are similar with a tilted angle of 45°. For better demonstration, measurement results in the actual environment of mobile handset are provided to effectively validate the proposed designs.

This paper presents a development of a machine learning (ML) based prediction model for large scale channel parameter (LSCP) estimation by analyzing the interaction of the multipath ray's information with the propagation environment. Utilizing the robustness of ML, a dynamic LSCP predictive model can be realized. The input parameters to the prediction model are transmitter (TX) and receiver (RX) positional coordinates, and the reflected rays' information such as the delay, angle of arrival, angle of departure, elevation angle of arrival, elevation angle of departure, and power gain. The proposed model was implemented using Random Forest. Ray tracing (RT) simulation was performed to calculate the input dataset of the LSCPs, and also the input datasets of the reflected rays. Cross validation was utilized to validate the model.

In this paper, the design and implementation of a wideband circularly polarized (CP) transmitarray are reported. The receiving/transmitting unit cell is designed by using magneto-electric (ME) dipole with polarization conversion from linearly polarized (LP) to CP. In addition, a full 360-deg geometric phase tuning range can be provided by rotating the transmitting CP element. As a demonstration, a single beam transmitarray is developed by utilizing geometric phase compensation technique. The results verify that the axial ratio performance can be improved within the whole operating frequency band due to the opposite phase response for the dual CP components. Moreover, this methodology can be easily extended to the design of multi-beam CP transmitarray with a cluster of LP feeds.

This paper presents design of a linearly dual-polarized and dual-wideband multi-ring microstrip antenna (MR-MSA) fed by two L-probes for a small ground plane. Two circular ring patches with a different size are printed on the top and middle dielectric substrates and two L-shaped probes arranged orthogonally are placed in the bottom substrate with a large thickness for dual-polarized and dual-wideband operation. Furthermore, the MR-MSA is surrounded by a cavity structure for stable gain characteristics. In this paper, the dual-band and wideband MR-MSA fed by two L-probes for a small ground plane is considered by using numerical simulation. The simulated results reveal that the cavity provides stable gain characteristics for a side of the ground plane more than 0.85 wavelengths at the center frequency of the lower band. It is also confirmed that better performance is obtained by the MR-MSA without the cavity for a smaller size of the ground plane.

This paper proposes, a design of optically transparent antenna arrays with dual polarization for mmWave communications. The proposed antenna is consisting of three radiating patches resonating at slightly different frequencies and has two ports to excite dual polarizations. The individual patch is fed by a 'T'-shaped probe in proximity. For display-integration, the antenna is modeled as thin-metal meshes, whose shape is rhombus with equal edge lengths to provide optical transparency. Antenna characteristics such as impedance bandwidth, gain, and polarization isolation are simulated. The optically transparent antenna shows fractional bandwidth of 17.2% and peak gain of greater than 8 dBi from 25.5 GHz to 30.1 GHz. It is confirmed that the proposed design is effective to broad 10-dB matching bandwidths with high gain of greater than 8 dBi.

An embedded dual-band dual-polarized base station antenna (BSA) array is proposed in this paper consisting of two low-scattering bowl-shaped antenna elements working at the lower band (LB) and five cross-dipoles operating at the higher band (HB). Such an array configuration naturally has an ability to mitigate the negative effect on the HB antennas' radiation pattern caused by the presence of adjacent LB antennas. In this paper, a new LB antenna loaded with metal chokes is proposed to reduce its scattering to the HB radiation. The results obtained with conventional bowl-shaped LB antenna and with choked LB antenna are compared to demonstrate the superiority of this de-scattering method. The simulation results show that the HB performance is significantly improved with the help of metal chokes while the LB performance remains nearly unchanged.

The 5G, 6G of future wireless technology has brought a growing demand for different types of electrically small or large antennas, which are highly efficient, directive, and provide wideband coverage. We have presented here a compact and highly efficient slotted-array antenna technology operating at a millimeter-wave frequency range to be used for the emerging applications of 5G wireless backhauling and mobile radio services. The antenna consists of two conducting plates, with the upper plate having a slotted array in the form of a spiral. A waveguide forms between these plates and supports outward traveling TEM waves. The antenna was simulated using CST to validate the design mechanism. The proposed antenna achieved an extremely high gain of 27.2 dBic. The antenna has shown a high 3dB gain bandwidth of 4.6 GHz, ranging from 33.2 GHz to 37.8 GHz, and an overall wide bandwidth of 13%.

The thermal behavior of a frequency-reconfigurable wearable textile antenna is investigated in this paper through infrared thermography. The relationship between the temperature of the textile antenna and the input power is experimentally considered to identify the antenna hot spots. It is found that, the highest temperature point is mainly at the tuning component location, which is consistent with the loss predictions from electromagnetic simulation tools. A clear correlation is confirmed between the radiation efficiency and temperature of the varactors used as tuning elements. It is also observed that tuning frequency remains stable despite the antenna input power variations within the range from 21 to 521 mW. The presented preliminary results demonstrate the use of infrared thermography as a valuable tool for characterization of thermal safety margins of wearable devices and for imaging of losses in reconfigurable antenna technology.

This paper aims at exploiting the expected massive deployment of RF signals by proposing a low-cost ultrawideband (UWB) planar antenna with a bandwidth of approximately 23 GHz ranging from 10.9 to more than 33.66 GHz. Using different slots on patch and ground plane and through feedline transitions the UWB requirements are achieved. Simulation results show that a proposed antenna with optimized dimensions can enhance the impedance matching and increase the bandwidth without a much effect on the antenna performance. The antenna is fabricated, and the simulated results are validated by the experimental measurements.

A hybrid through-the-wall imaging method is presented in this paper. It is based on the use of an iterative technique performing a regularization in the framework of the variable-exponent Lebesgue spaces. The exponent function is computed using a preliminary image obtained through the singular value decomposition method. The effectiveness of the approach has been tested by means of experimental data acquired in a laboratory environment.

It is desirable to detect buried objects such as land mines at standoff distances and Ground Penetrating Synthetic Aperture Radar (GPSAR) is one technology that has potential to detect some buried objects. One challenge with using GPSAR is that responses from the surface of the ground can be similar in magnitude to the buried objects. To try and remove some to these responses, the surface profile of the ground was measured with high resolution optical sensors. This surface profile was used to model the radar response of the ground using gprMax. The modelled response was then subtracted from the measured radar response to reduce the response from the ground and better reveal the responses of the buried objects.

Fast and accurate characterization of concealed threats and benign objects is of great importance for increasing the efficiency of mm-wave imaging radar personnel screening systems in airports. Correctly classifying low-loss and lossless materials is essential in detecting threats. Previous work developed a real-time, fully automatic algorithm for characterizing lossy vs. lossless materials. This paper extends the mm-wave image-processing-based method to distinguish low-loss media, such as paper vs. lossless materials, that include explosives. The developed method is verified experimentally by applying it to experimentally measured radar data generated by a 10-40 GHz wideband laboratory airport screening prototype.

This contribution assesses the impact on the image quality of the number of transmitting (TX) and receiving (RX) channels of a freehand millimeter-wave imaging system. The freehand imaging system comprises a compact radar module that can be moved by hand while its position is tracked. This enables the use of synthetic aperture radar techniques to obtain high-resolution images with a compact handheld scanner. The employed radar module, capable of capturing data from 400 TX-RX channels per acquisition, was used to scan a test target and the reflectivity image of the area under scan was generated considering several TX-RX configurations. Results show that, as expected, the higher the number of considered TX-RX channels, the better the quality of the retrieved image. However, the target can be accurately reconstructed with configurations that employ a reduced number of TX-RX, reducing the computational cost of the imaging system and increasing the acquisition speed.

This contribution presents the main objectives and achievements of the SAFEDRONE project, devoted to the development of airborne-based high-resolution Ground Penetrating Radar (GPR) systems for the detection of buried landmines and Improvised Explosive Devices (IEDs). The overall goal of the project is to take advantage of the ability of Unmanned Aerial Vehicles (UAVs) to enable a contactless, safe, and fast scanning of the area of interest, together with the capability of Synthetic Aperture Radar (SAR) systems to provide high-resolution radar images. Down-Looking and hybrid Forward-Looking/Down-Looking architectures have been tested throughout the project in order to determine which of them provides the best detection results (depending on the scenario, and geometry, composition, and depth of the buried targets). To achieve the required accuracy to enable GPR-SAR processing, precise positioning and geo-referring subsystems have been integrated within the UAV. Results of the validation tests conducted in realistic scenarios are presented.

The quantitative imaging of breast tumors through microwave measurements is addressed. An innovative solution approach based on the System-by-Design (SbD) paradigm is proposed to achieve a highly accurate reconstruction with limited computational resources. Towards this end, the inverse scattering problem (ISP) at hand is reformulated in terms of the differential electromagnetic (EM) quantities with respect to a reference/healthy scenario, enabling the exploitation of prior knowledge regarding the breast composition. The performance of the developed approach is investigated in numerical simulations considering realistic breast phantoms. The results indicate that highly accurate reconstructions are achieved even under a significant noise level. Furthermore, the developed approach only requires few minutes of processing, hinting at its applicability to real-world scenarios.

Electrical properties, conductivity and permittivity, of biological tissues are widely investigated because they provide crucial knowledge in different biomedical applications, for example in electromagnetic dosimetry and hyperthermia treatment planning, where is very important to quantify the induced specific absorption rate by a radiofrequency field. In this framework, a possibility is to retrieve the electrical properties starting from the measurements of the radiofrequency field collected inside a magnetic resonance scanner. To this end, in this paper, a learning approach based on supervised descent method is proposed in order to improve the efficiency of the reconstruction methods typically used in the literature. The approach is tested in the case of a 2D scenario mimicking a human head.

Early detection and resection of colon polyp is the best way to reduce colorectal cancer (CRC) mortality. The current method for early detection is colonoscopy, which has a limited field of view, and its efficacy is highly dependant on the endoscopist's experience and colon preparation. This work presents a device for combining microwave imaging with optical colonoscopy. The challenges of this new microwave imaging system are presented, such as the unknown distance to the colon mucosa, which leads to undesired scattered fields and, the antenna size limitations. Four dynamic calibration techniques are proposed to remove the effects of the undefined distance from the imaging region to colon mucosa. These calibration methods are based on averaging the colonoscopy trajectory frames and subtracting the calibration set from the current frame. The phantom preliminary results evidence that these calibration methods delete the undesired scatters satisfactorily.

Microwave Imaging (MWI) has been explored as an alternative to conventional breast tumor screening methods. It is acknowledged that benign and malignant tumors can be distinguishable by their architectural features: benign tumors are often round with well-defined margin, while malignant tumors have an ill-defined margin and are micro-lobulated or spiculated. We present a MWI-based systematic analysis of malignant and benign breast tumors of different sizes, to evaluate if its characteristics allow differentiating the images. To this end, we performed measurements on a dry MW setup, using a slot-based antenna in the 2-5 GHz frequency range to scan an anthropomorphic breast phantom. We placed inside eight malignant and benign tumors with 3, 4, …10 mm average radius, one at a time. This study shows that both types of tumors can be detected, but not distinguishable only via MWI. Smaller tumors become harder to detect, the 3 mm tumor being unreliably caught.

Microwave imaging is a promising candidate modality for the detection of fractures in superficial bones. We propose a simple dedicated experimental setup and use it to evaluate experimentally the feasibility of detection and location of thin transversal fractures in an animal bone. A single small Vivaldi antenna scans the bone along its length in two longitudinal planes, and collects the monostatic scattered fields in the 8.3-11.1 GHz frequency range. The image is reconstructed using a wave migration algorithm. Tests were carried on an ex-vivo animal leg bone with an induced transversal fracture. The results showed that transversal bone fractures can be detected down to 0.35 mm thickness. The system is attractive for a practical application because it is contactless, operated in air, non-ionizing, simple and comfortable for the patient. It can be used e.g. by first responders in the field, or in low-income settings.

The automotive industry, especially smart, intelligent connected vehicles (ICV), is evolving towards more intelligent and electrified systems. Vehicles equipped with autonomous driving assistance systems are becoming increasingly popular, and the functions and performance have significantly improved. However, the examination of autonomous driving assistance systems and wireless telematics systems are not included in the existing standards for automotive electromagnetic compatibility. A method proposed by China Automotive Engineering Research Institute Co., Ltd (CAERI) is introduced in this paper. The aim of the paper is to discuss the electromagnetic safety test method of intelligent connected vehicles equipped with wireless telematics systems and/or advanced driver assistance systems, which further specifies the electromagnetic immunity test conditions, technical requirements, and evaluation methods for intelligent networked vehicles.

This paper suggests an innovative approach to define and perform tests of communication systems in cars. The test concept requires the placement of the vehicle under test on a planar turntable in an anechoic chamber. Software-defined multimode transceiver modules, referred to as radio heads, are placed in a quarter circle or half circle around the car at an adequate distance. This setup allows flexible, realistic, reproducible and dynamic over-the-air testing of the cars communication systems in the sense of a virtual drive test. One key topic is the definition of sufficiently realistic test scenarios based on real outdoor scenarios. The full description of those scenarios requires a large number of parameters and performance indicators, making it impractical to perform this derivation following a classical straight-forward approach. Therefore, our concept foresees the use of machine learning algorithms.

Given the advancement of technologies related to automotive communications, working groups have been formed to define the methodologies for Automotive Over the Air (OTA) Measurements. The 5GAA test plan [1] defines two methods for OTA radiated power and sensitivity measurements, Direct-OTA and Combinational Method. In this paper the OTA measurement results performed on a full vehicle at near field distances are reported. The results are presented using the metrics which are relevant to automotive technologies. Direct-OTA results and estimated Baseline far field results are compared. The feasibility of measuring at a distance closer than far field is examined. Measurement time reduction for alternative measurement methodologies is evaluated.

Virtual drive tests using the over-the-air/vehicle-in-the-loop method are becoming an essential part of testing vehicular radio systems. Different approaches address the question which link scenarios and channel environments are relevant, and should be tested. Up to now, this question has not been fully answered. This paper deals with the identification of challenging scenarios for the wireless transmission standards LTE and ITS-G5 based on jointly performed drive tests, and how these can be transferred into a virtual test concept. In the case of LTE, the focus is on the transition region between different mobile radio cells (cell edge). We have reproducibly observed that the achievable data throughput drops significantly at cell edges compared to the cell centers. For ITS-G5, the communication limit was examined as a function of the distance and visibility conditions between two communicating vehicles.

EMC testing is typically performed in shielded absorber lined enclosures, and the design of these chambers have evolved over the years to take advantage of improvements in material technology, and changes in the way tests are performed. Other RF measurements like antenna pattern or over the air (OTA) communication performance measurements are also performed in shielded absorber lined enclosures for many of the same reasons. One of the main reasons is to provide RF isolation from the outside environment to prevent external RF signals from interfering with the device under test (DUT) or vice versa. Another is the approximation of a free space environment with well controlled reflections. The degree to which this is required differs for the different measurement types.

Multi-functional metasurfaces have attracted considerable attention over the recent years. However, the passive multi-functional metasurface is subjected to fixed functionalities. In this work, we propose the design of a two-dimensional dynamic metasurface where the meta-atom is individually addressable by an elaborately designed bias system. Three different kinds of holographic imaging containing focusing spots, numbers, and letters are fulfilled at different working frequencies.

A high-index dielectric scatterer is camouflaged with respect to a low-index dielectric reference by incorporating buried metasurfaces within the scatterer's volume. The metasurface-tuned scatterer is analytically modeled with transmission lines and a proof-of-concept prototype is fabricated and measured in the X-band. Experimental results of the scattering suppression phenomenon is presented in the near-field and far-field regions for both normal and oblique incident illuminations. This study presents metasurface-tuning as a frequency adjustable, polarization insensitive alternative tuning solution to efficiently camouflage dielectric scatterers, such as mechanical joints in seamed-radome structures.

Herein, we propose a method for the design of compact metasurface pairs which is based on an integral equation formulation. The novelty of this method is the ability to be used for metasurface pairs with arbitrary shape and orientation. The validity of the method will be shown for a fundamental case.

An accelerated Integral Equations (IE) field solver for determining scattered fields from electrically large electromagnetic metasurfaces, with both normal and tangential susceptibilities, utilizing Fast Multipole Method (FMM) is proposed and demonstrated in 2D. In the proposed method, practical general metasurfaces are modeled as a zero thickness sheet model described with surface susceptibilities, and where the total fields around it satisfy the Generalized Sheet Transition Conditions (GSTCs). While the standard IE-GSTC offers fast field computation compared to other numerical methods, it is still computationally demanding when solving electrically large problems, with a large number of unknowns. Here we accelerate the IE-GSTC method using the FMM technique. Using a numerical example, the speed improvement of the FMM IE-GSTC method O(N^(3/2)) over the standard IE-GSTC O(N^3) method is confirmed, when both tangential and normal surface susceptibilities are present.

Machine design of metasurface antennas concerning relevant figures of merit, such as the realized gain, typically requires 3D computationally intensive full-wave simulations due to the more or less complex feeding structure. However, via domain decomposition analysis, we show here that the modelling of the feed and the antenna itself can be effectively decoupled in many, if not all, relevant conditions. We then propose an accelerated design and optimization scheme in which the electrically large antenna is only simulated with well-known 2.5D fast algorithms, significantly reducing the design complexity.

Directional modulation (DM) using multiport compact antennas shows some limitations when transmitting multiple independent beams. In this communication, we propose adding a monopole to a multiport compact stacked patch antenna in order to gain an extra degree of freedom in the transmission of DM. The improvement in security that can be achieved with the resulting antenna will be evaluated through bit error rate (BER) simulations for different configurations with two independent beams.

Nowadays, one of the most promising developments for a safer and more sustainable mobility is the Connected and Autonomous Vehicle (CAV), where the Advanced Driving Systems (ADAS) and connectivity cooperate and take advantage of each other. The Cooperative Adaptive Cruise Control (CACC) might be one of the beneficiaries of such collaboration, being in turn the key enabler of platooning. While this cooperation improves safety and driving efficiency, it also opens the door to increasingly sophisticated cyberattacks. This paper analyses a CACC based platoon model approach in which communication is vulnerable to jamming attack. Jamming attack refers to to an unwanted signal radiated by a malicious device intended to impair the quality of an operating link. Two different platooning variants are compared taking diverse scenarios into account. The presented approach shows how platooning can be susceptible to cyberattacks and some directional measures to mitigate it are proposed.

In this paper, the diffraction-limited imaging capabilities are presented of a focal plane array (FPA) of antenna-coupled direct detectors at submillimeter wavelengths. The FPA prototype is a tightly sampled, 12-pixel array that was developed in a 22nm CMOS technology and covers a relative bandwidth of 3:1, from 200GHz to 600GHz. We are currently developing a quasi-optical (QO) setup to perform imaging using active illumination of the FPA. The images created by this QO setup and FPA will be the first demonstration of achieving diffraction-limited angular resolution, making this FPA very attractive for future passive THz imaging applications.

Fourier-based radar processing algorithms have attracted a lot of interest among imaging techniques mostly because they are extremely fast. Moreover, such techniques can be integrated with a Multiple-Input Multiple-Output (MIMO) effective aperture, able to alleviate the hardware constraints, to form a cost-effective imaging system that can retrieve an estimation of the scene in real-time. The proposed technique leverages the phase center approximation and a multistatic-to-monostatic data conversion to render the back-scattered measurements compatible with fast Fourier processing. Whereas the phase center approximation is applicable for imaging in the far-field of the synthesized aperture, in the near-field, a more sophisticated aperture design should be considered to reduce the distortion in the reconstructed images. This paper presents a theoretical study for a sparse aperture design and the optimization of the aperture layout in the context of the phase center approximation validity for near-field imaging facilitated by Fourier-based reconstructions. Furthermore, it proposes a GPU accelerated reconstruction algorithm able to form 3D images in a few milliseconds with low-cost hardware.

We report on the progress towards a dual-band leaky-wave lens antennas operating at 210-240 GHz and 500-580 GHz simultaneously. The antenna can be used in a focal-plane array to be placed in the focus of a parabolic reflector, achieving overlapping beams and constant gain on-sky in both frequency bands. Such capability is essential for the COMETS spectrometer and radiometer that is currently under development at NASA/JPL. In this contribution, we emphasize the analysis and synthesis of the leaky-wave stratification for this antenna, which is then validated using full-wave simulations. The performance of the lens antenna in the quasi-optical system is presented. We report on the progress towards a submillimeter-wave dual-band lens antenna prototype.

In this study, a multilayer perceptron (MLP) neural network is utilized to inversely design a rectangular microstrip patch antenna. The MLP network maps the input features, including the resonant frequency, directivity, realized gain, and time-domain representation of the S-parameters, to the output that is the antenna geometrical parameters. Especially with the time-domain representation of S-parameters added into the input features, the prediction error of the antenna geometrical parameters can be decreased dramatically. The mean square error (MSE) and mean absolute error (MAE) are 0.00432% and 0.484% for the test dataset, respectively. The promising results verified that incorporating the time-domain representation of S-parameters into the features could effectively improve the prediction accuracy of the MLP network for inverse antenna design.

A topology optimization technique based on exact reanalysis is proposed within method-of-moments formalism. The optimization is formulated over a fixed discretization grid by performing general block structural modification. The procedure is based on an inversion-free evaluation of topological sensitivities, constituting a gradient-based local step that is iteratively restarted by the genetic algorithm. The proposed method sacrifices structural resolution at the expense of lower computational time and direct manufacturability. The method's validity and effectiveness are demonstrated in two examples.

This paper investigates through the wall imaging (TWI) problem via machine learning. To solve the TWI problem in presence of the wall, a Convolution Neuron Network (CNN) is proposed. The detection of the scatterers behind the wall when there is a strong reflection from the front wall is very challenging. Several microwave imaging algorithms have been introduced to extract the unknown parameters of the wall and mitigate the wall clutter to predict the location of the target. This process is very time consuming even though it has accurate results. In this paper we developed a method for exploiting the complex information for TWI problem by using a CNN that accepts complex numbers from receiver to predict wall thickness, material, and location of the target behind the wall at the same time. We show that our proposed model can predict these parameters with an accuracy of 92.6%.

A fundamental problem in electromagnetics is the shaping of the field intensity distribution in a given region of interest. Several strategies have been designed to address such issue in several and different applications, ranging from hyperthermia to wireless power transfer. In this contribution, we focus our attention on MRI shimming. Usually the shimming (or leveling) of the radiofrequency field B1+ can be performed by using particular materials characterized by high permittivity values or by acting directly on the primary sources (i.e., the excitations of the radiofrequency coil). Herein, the proposed procedure exploits the field intensity shaping paradigm to design the primary sources in such a way to ensure a uniform field and to control the specific absorption rate inside the biological region under investigation

The optimization of mode excitation coefficients in linear periodic arrays of multi-mode antenna elements is studied for grating lobe reduction. A novel beamforming architecture is proposed with a new optimization problem based on equi-amplitude element excitations for optimal power efficiency. The capabilities of the proposed synthesis approach on suppressing the grating lobe for wide scan angles, and on maintaining the peak gain at the steering angle are analyzed. A 16-element 0.7-wavelength spaced array of dual-mode circular patch antenna elements is used for demonstration purposes. It is shown that a good performance trade-off is achieved when the excitation amplitude of the high order mode is restricted to a sufficiently large value. The ratio of the peak gain outside the main lobe to the gain at the angle of steering is reduced up to about -15 dB and -14 dB for scanning towards 30 and 45 degrees off-broadside, respectively.

Microstrip patch antennas are generally narrowband and therefore their Q-factor is an important design parameter. To minimize Q-factor, current optimization has been successful in obtaining bounds for arbitrary shaped antennas. This formulation relies on a method of moments implementation. Here, current optimization is extended to microstrip antennas. Allowing antenna designers to obtain minimum Q-factor for given constraints. Further, the bound can provide a trade-off of several parameters when considering Q-factor.

The optical behavior of a terahertz imaging system employing a train of four identical off-axis parabolic mirrors with oblique incidence angle illumination is investigated in this work. The aperture filling and aberrations of a single off-axis parabolic mirror when illuminated by a Gaussian terahertz beam at its focus point is measured and simulated. The amplitude of E-field in transverse electric (TE) and transverse magnetic (TM) polarizations at target plane reveals a significant cross polarization, even when there is zero cross polarization at the source beam, amplitude of which is ∼ 33% of TE polarization. The investigation of the E-field on the detector plane reveals that this ratio is ∼ 1.5% at the detector plane, and the cross polarized E-field at the target plane is rotated back to co polarization. Although its amplitude is negligible, the TM distribution at detector plane is bimodal and tilted about the optical axis.

Photoconductive antennas (PCAs) are promising candidates for millimeter-resolution imaging applications. In the past, our group investigated their properties under pulsed laser illumination only in transmission, with the receiver being a power detector. Here we consider a second PCA as the receiver and develop a quasi-optical (QO) time-domain link for investigating the coupling between the transmitter and the receiver. Specifically, a field matching technique is used to evaluate the short-circuit current of the receiver. Based on this current, the spectral mutual coupling between the two PCAs, including the QO link can be evaluated. Moreover, a time-domain Norton circuit in reception is proposed to quantify the detection. A marching-on-time technique is used to evaluate the response of the receiver. As an example, a bow-tie antenna feed is simulated to show the coupling and the device response.

Three coherence factor based methods are analyzed and then incorporated into the imaging procedure of our near-field millimeter-wave radar security scanning system. The performance of these methods is verified by multiple simulations and experiments. The simulation and experimental results show that these methods are effective in decreasing the side lobe levels of the reconstructed images by Advanced Imaging Technology, hence improving the image quality of our imaging system.

This work deals with the retrieval of the electromagnetic properties of two-dimensional (2D) and three-dimensional (3D) domains starting from microwave scattered data. Within this context, multi-resolution (MR) methods can yield accurate, robust, and computationally-efficient solutions, overcoming single-resolution (SR) inversion strategies. As a matter of fact, they reduce the degree of non-linearity of the inverse scattering (IS) problem, providing at the same time an effective regularization of its solution. The aim of this work is to (i) highlight the main concepts and principles of MR strategies, (ii) provide an overview of the most recent advances in this field, and (iii) introduce an innovative overconstrained (OC-MR) solution strategy for solving fully non-linear IS problems.

A novel direction-finding method for digital metasurface is proposed and verified. Considering the phase-control capability of the digital metasurface and the limit of only a single receiving channel, time modulation technique is introduced herein to modulate the phase of incident wave periodically from phase 0 to π. Multiple harmonics are thus generated and carry the angle information in the single-channel signal. With the discrete Fourier transform (DFT) and harmonic characteristic analysis, the direction of arrival can be easily estimated from the harmonics. Simulation and experiment results are provided to verify the feasibility of the proposed method.

This work presents a radiofrequency (RF) performance review of a conductive ink dispensing process for RF applications. This innovative process allows to functionalize existing objects like plastic cases for adding a RF function. It can print devices on a substrate placed horizontally or in a tilted position. The main purpose of this work consists in showing the feasibility of this process. First, Coplanar transmission lines are printed with silver ink on horizontal substrate by a simple configuration. It exhibits a performant attenuation coefficient: α4GHz=0.021±0.007 dB/mm. In a second part, a 6-axis robot is used for improving the 3D process, coplanar transmission lines are also printed and exhibit a performant attenuation coefficient: α4GHz=0.060±0.009 dB/mm. Finally, coplanar lines are printed on tilted plastic substrate and then measured. The scattering parameters of horizontal and tilted substrates are similar and exhibit a good performance in the range of 0 to 4 GHz.

Design of antenna structures for real-world applications is a challenging task that often involves addressing multiple design requirements at a time. Popular solution approaches to this class of problems include utilization of composite objectives. Although configuration of such functions has a significant effect on the cost and performance of the optimization, their specific structure is normally determined based on engineering experience and does not involve auxiliary investigations oriented towards adjustment of process efficiency. In this work, the effects of used functions and their composition on performance and cost of the bi-objective optimization process are investigated. The balance between the requirements is tailored to the problem at hand based on visual inspection of functional landscapes. The analyses are performed on a case study basis using a planar, multi-parameter antenna optimized for minimization of footprint and reflection within the 3.1 GHz to 10.6 GHz range. The numerical results show significant differences between the performance of the obtained solutions, as well as the computational cost of the optimization. The best geometry found using one of the considered objective functions is characterized by an in-band reflection of -9.6 dB and the footprint of only 171 mm 2 .

The optimal planning of passive reflective skins installed on the building facades for implementing next-generation smart electromagnetic environments (SEEs) is addressed. Towards this end, a customized System-by-Design (SbD) strategy is exploited to yield the best trade-off solutions between maximum coverage enhancement within selected regions of interest (RoIs) and overall cost/environmental impact. A suitable binary coding strategy is adopted to define the degrees-of-freedom (DoFs) of the planning problem at hand, which is solved by means of a customized binary genetic algorithm (BGA) integrated with a learning-by-examples (LBE) prediction tool for the computationally-efficient evaluation of the urban wireless coverage. An illustrative numerical example is shown to assess the effectiveness and potentialities of the proposed planning strategy in a realistic scenario.

a novel wide-angle rasorber with a wide transmission window and two wide absorption bands at both sides of the transmission window based is presented in this article. The rasorber consists of a metallic absorption layer (loss layer) and a metallic FSS transmission layer (lossless layer). The transmission channel is achieved by a staggered grid slot. An equivalent circuit model is proposed to explain the fundamental operating principle of this model and how to achieve the characteristic of the transmission window within the absorption band. The simulated results show that a flat less than 1 dB transmission window can be obtained from 9.5-10.8 GHz, and the -10dB absorption bands are 6.2-8.9 GHz and 13.7-22 GHz under TE polarization. The transmission bandwidth and absorption bandwidth of FSR under TE and TM are almost the same. At the same time, oblique incidence can reach 50°, with good angular stability

This study investigated the performance of a Mosaic Frequency Selective Surface (MFSS) for two different applications: optical transparency and absorber. The MFSSs comprising the transparent MFSS fabricated from the polycarbonate substrate (permittivity, εr of 2.9) and the absorber MFSS that utilized the Polyethylene Terephthalate (PET) substrate (εr of 2.7). For optical transparency application, the MFSS unit cell was composed of a conductive metallic element design that integrates the Koch fractal and the double hexagonal loop, while the resistive MFSS unit cell with sheet resistivity of 100 Ω/sq was utilized for the absorber application, were fabricated on the aforementioned substrates. Based on the results, it was concluded that the transparent MFSS yielded a wideband stopband and passband responses (fractional bandwidth (FBW) > 50%) with a low cross-polarization (-37 dB), and a wideband absorptivity response with FBW of 121 % was achieved with the thin MFSS absorber

Electromagnetics today underpins all modern information and communication technologies. Increasing deployment of telecommunication services is urging RF industry to carry out better and better electrical designs, where a single device is no longer conceived to perform a single functionality, but rather multiple tasks at the same time.

Unfortunately, much electrical design activity is still based on brute-force computational simulations to predict the actual physical behavior of electromagnetic devices.

In our work we use computational electromagnetics as an actual design tool, rather than just an analysis one. This can be achieved by shrinking computational electromagnetics into a simple parameterized equivalent circuit form, from which an electrical engineer can get actionable design insights.

Our efforts stand upon model order reduction techniques, such as the reduced-basis method. However, a new physics-based strategy is carried out to provide further physical insight of the electromagnetic device under analysis and, ultimately, extremely valuable design information.

Windows with advanced thermal properties are commonly used in the railway industry. However, these glasses suppose a problem to the RF signal transmission and many solutions are studied to avoid the attenuation of the electromagnetic waves. To characterize the attenuation of the different windows different systems can be used. In this paper, a system with a closed metal chamber is studied as it is closer to the real situation due to its similarity to a wagon. Simulations and experimental measurements are carried out to compare this setup with the anechoic chamber one.

To deliver the high capacity and throughput goals for 5G, the effective use of millimeter-wave spectrum is necessary. These high frequencies incur in greater attenuation due to path loss and blockages when compared to sub-6 GHz, necessitating the use of directional antennas at both ends of the communications link. These are most likely to be implemented by means of antenna arrays and beamformers in a highly integrated form within the RF-transceiver. The radio environment at these frequencies is known to be highly dynamic in both spatial and temporal domains. Hence, Over-the-Air conformance testing of such systems will be necessary, since traditional conducted non-spatial test methods will not predict the radiated performance in space. This paper presents a novel OTA test method that facilitates the excitation of a device under test from multiple dynamic angles of illumination in azimuth and elevation planes, thus representing realistic operating propagation conditions.

A new design of microwave medium power calorimeter is introduced in this paper, based on principle of water calorimetry. Calorimeter is designed to measure coaxial radiofrequency (RF) power 1 W -100 W in power range, and 10MHz - 7.5GHz in frequency range. Whereas in this paper, only 1W - 10W power level and 2GHz - 3GHz frequency range are investigated, due to current power amplifier limitation. Comparing to conventional medium power measurement based on coaxial attenuator or directional coupler, proposed method displays explicit traceability chain from RF medium power to DC medium power. In proposed calorimeter system, calorimetric thermopile is designed with clinging brass blocks. Water temperature is homogenized in block and transient calorimetric results are investigated, showing that 5 minutes rest time is needed to reach system thermal equilibrium. Effective efficiency between RF and DC power is investigated for 1W and 10W power levels, with less than 2.4% and 2.8% respectively in relative standard deviation.

This paper presents the study of arrays composed of quarter-cylinder dielectric resonator antennas (QCDRA). The proposed antenna array has been optimized to operate at 1.575 GHz (L1-band of GPS). Initially, the design of the single antenna is presented. Then, the array performance using four different arrangements of elements is discussed for broadside radiation. In order to assess the performance of the proposed array, a study on the beam steering capabilities has been carried out and the resulting radiation patterns are shown and discussed. It is demonstrated that the proposed antenna design allows obtaining good performance in terms of axial ratio in the analyzed beamforming cases and, due to its compactness, it is a good candidate for multi-antenna high-precision GPS receivers.

This paper presents a Wilkinson power divider (WPD) capable of suppressing unwanted bands up to 16th harmonic with high isolation. In this WPD, a lowpass filter composed of a main resonator and three bended stubs are used to guarantee a wide stopband. The presented WPD illustrates suitable performance at 0.85 GHz for GSM applications. Isolation between of output ports, input return loss and insertion loss are better than 24 dB, 20 dB and 3.4 dB, respectively.

In glaciology, Ground Penetrating Radar (GPR) are frequently used to characterize electrical and physical properties of glaciers and snow coverages. An application is the estimation of the snow water equivalent of glaciers, coming from the knowledge of internal features of the glacier itself, such as its depth and density. For glacier monitoring, the usual frequencies space from few MHz to hundreds of MHz. Depending on the compromise between the penetration depth and the spatial resolution, the working frequency was determined. In this work, we designed, developed and measured a 300 MHz antenna used for this purpose. The shape and size were modeled in order to be used in portable systems; therefore, it was important to have light and small radiators. For this reason, we implement a novel planar inverted-F antenna (PIFA) design with capacitive load, reaching small dimensions compared to the wavelength.

A new design of a patch antenna with a broad bandwidth and high gain is demonstrated in this work. The 32 GHz wideband highly-directive patch antenna is covered with a novel single layer metamaterial-based superstrate to attain a significant gain improvement over a wide bandwidth. A new multi-resonant dual face unit cell with four asymmetrical patches and apertures is used as a building block of the superstrate. The superstate performing as a frequency selective surface (FSS) offers a partial reflection that is based on the positive phase gradient concept. The results show a 10.5 dB increase in the gain which is about 210% enhancement over the single antenna gain at 32 GHz. The proposed antenna attains a broad impedance bandwidth of 32-43.1 GHz (29.6%), and a 3-dB radiation bandwidth of 12.6%.

The problem of gain estimation of a superdirective end-fire dipole-based array is discussed. The current method to compute the gain, for a given element radiation efficiency, is based on the array factor (AF) theory. This work is intended to show that an equivalent formulation can be done using the Spherical Wave Expansion (SWE) theory. Besides the interest in validating the theory, the main objective is a better understanding of the radiation and attenuation phenomena that occur in compact and superdirective arrays. The limits in their practical implementations are imposed by the high sensitivity of the system. The SWE theory provides more information in the expression of the radiated field, thus unfolding the possibility to address the problem with lower sensitive solutions.

This paper explores the performances of finite antenna arrays optimized using the Interleave Parasitic Arrays Antenna (IPAA) concept. A prototyped IPAA of 36 elements is used to compare the simulated performances obtained using the scattering matrix extraction from the periodic model method and measurements with great accordance. Then, two large arrays composed of 1024 and 4096 elements are studied using the same simulation method. The results show that the IPAA concept is particularly suited for large arrays, with only a few edge elements showing degraded performances.

A wideband rectangular patch antenna based on complementary structure in two ports-configuration is presented. Electromagnetic analysis and a design of the mentioned structure in FR-4 substrate were performed. A very high matching bandwidth from 1 to 11 GHz (BW_RL≥10dB=10 GHz, 167%) was achieved. Two degrees of freedom were used to obtain this high matching behaviour (length and width of the slot). The analyzed two port-device has a bidirectional broadside radiation pattern. It shows good values of gain, radiation efficiency, and suitable radiation pattern from 4 to 7 GHz (BW_radiation=3 GHz), representing the 30% of the matching bandwidth and 54% of the radiation center frequency. A prototype was manufactured and measured. A very good agreement between the simulation and measurement results were achieved. The studied structure is simple, compact, of low cost, and easy and flexible to design. It can be used as a radiating element for broadband series fed arrays.

Electromagnetic Bandgap structures (EBG) are used along with patch antennas due to their ability to reduce the size of the antennas and enhance the performance parameters of the patch antennas. Many shapes of EBG are proposed in the recent times to meet the needs of wireless technologies in the future. This paper proposes a stub loaded oval ring patch antenna mounted on a serpentine shaped EBG ground. The patch antenna possesses dimensions of 18 x 18 x 0.8mm3. Miniaturization of 89.1% is achieved with the proposed antenna structure. The proposed patch antenna resonates at 4.28GHz, 6.15GHz, 6.78GHz and 12.15GHz. Peak gains of 1.1dBi, 1.3dBi, 2.8dBi and 2dBi are observed at 4.28GHz, 6.15GHz, 6.78GHz and 12.15GHz respectively. Bidirectional radiation patterns are observed at 4.28GHz, 6.15GHz, 6.78GHz and 12.15GHz. The radiation patterns are observed to be stable at the resonant frequencies.

Design, fabrication and test of a dual-linearly polarized wideband printed planar monopole antenna is presented. The proposed configuration consists of two orthogonal CPW-fed modified octagonal monopoles with low mutual coupling. It is developed to be used in a wearable antenna system application to probe the electromagnetic field, with frequency in the range 0.7-3.5 GHz (5:1 bandwidth), incident on a professional user. The reasonable agreement obtained between simulated and experimental results has validated the proposed design approach and provided the proof of concept.

The rectenna is the basic fundamental element for RF energy harvesting. The development of efficient rectennas requires the implementation of some impedance matching technique between the rectifying circuit and the antenna element. An impedance matching technique inspired by the inset feeding of microstrip patches is proposed in this work. The technique keeps the size of the rectenna unchanged and does not require any additional components. An application example operating at 5.8 GHz and using a cheap FR4 substrate is presented.

This paper analyzes the design of a semi-transparent Planar Inverted-F Antenna (PIFA) to operate in the 5G band. The proposed antenna consists of a set of metallic wires that form a grid which configures the conductive parts of the antenna. This new radiant element offers an adequate response in terms of gain and impedance matching. On the other hand, it can be easily manufactured using 3D printing techniques. The semitransparent element has been integrated into a 2x2 subarray to analyze its application in MIMO systems. The subarray has been tuned to provide port isolation, good impedance matching, envelope correlation coefficient and radiation characteristics which are desired for MIMO applications. The proposed element offers utility to implement large antennas in array configuration and, at the same time, allows visible light to pass through it.

The equivalence and differences between some different approaches to efficient Wireless Power Transfer are explored analytically. Design methods for transmitting arrays intended to wirelessly feed a receiving device can be found in the scientific literature under different framworks such as Near-Field Focusing, microwave device design or MIMO communications. However, those apparently different approaches result in equal or at least very close solutions. In this communication, the advantages, drawbacks or equivalences of these techniques are analyzed, and some simulations are carried out to support the conclusions. Some interesting future research lines are also highlighted.

IoT infrastructure involves billions of devices that must be self-sustainable. Using ambient energy sources to power IoT devices is a promising solution. Ambient RF and thermal energy (diurnal temperature fluctuations) harvesters have great potential since both are available continuously. Smart integration is required for these two harvesters to create synergy and collect more energy. Here, a dual-purpose triple-band heatsink antenna for multi-source ambient energy harvesting is presented. Heatsink antenna serves as a receiving antenna for the RF energy harvester and serves as a heatsink for the thermal energy harvester (TEH). Co-optimization of the heatsink antenna is performed in Ansys HFSS and Ansys Fluent simultaneously. Heatsink antenna operates at GSM900, GSM1800, 3G bands with measured gains of 3.8dB, 4dB, 5.3dB respectively. Antenna gain is doubled (~3dB) and the TEH performance is tripled (200%) when the heatsink fins are integrated, emphasizing the benefit of the co-design and smart integration via heatsink antenna.

In this paper, a method for synthesizing multi-feed antennas is proposed. The Eigenvalue analysis of the scattering matrix of a multi-feed antenna has been used to synthesize different types of excitations. We have shown that the eigenvectors in the null space of the scattering matrix act as the building blocks of the excitation vectors for optimum power combination. To bring more flexibility, we propose two different scenarios to fit the design restrictions: (A) antenna ports with different input power levels and equal input impedances, and (B) equal input power levels and different input impedances. Based on simulation results of a four-port half-wavelength dipole both scenarios yield the same power combining for the multi-feed antennas. Also, we studied the effect of the feeds' weighting vector on equivalent isotropic radiated power (EIRP). It can be concluded that the EIRP in the multi-feed antenna is not a linear function of input power.

We present fully planar, low-cost and easy to fabricate metamaterial-based Substrate-Integrated Waveguides (SIWs) and Slot Antennas for 5G Communications. The SIW is entirely planar since it is designed using series of side-by-side broadside-coupled complementary split-ring resonators (BC-CSRRs) etched on top and bottom metal ground surfaces of a dielectric substrate. This metamaterial-inspired structure replaces the vias of a classical SIW by providing a negative dielectric effective material parameter behavior which results to the block of the wave propagation to the direction perpendicular to the axis of propagation. Using this structure as a waveguide, slot antennas are consequently designed, by the proper etching of slots on the substrate. Coaxial cable excitation perpendicular to the circuits' plane is applied, avoiding the design of complex in-plane matching circuits.

The radiation characteristics of a series-fed array of 1D Leaky-Wave Antennas (LWA) are reported. A study of the proper transition between antennas, as well as the antenna design is performed, showing how to reach an optimum overall performance to keep the desired radiation pattern with good efficiency. Theoretical examples are shown for the 900 MHz UHF band. Finally, simulated results are obtained for a practical design in planar Half-Width Microstrip Leaky-Wave technology.

The performance of a single bidirectionally-fed scanning leaky-wave antennas for low-cost amplitude monopulse synthesis, is compared to the most conventional use of two tilted antennas. The main advantages and drawbacks are demonstrated in detail with a practical design for direction finding in the 2.4 GHz ISM band. It is demonstrated that leaky-wave antennas offer a much more compact and low-cost design, which reduces the near-field zone for proximity sensing. However, the frequency beam-squinting must be considered for accurate operation in the entire bandwidth.

The design, manufacture and testing of a micro strip leaky-wave antenna in the UHF band is reported. The antenna is fabricated using low-cost materials and handmade techniques. This activity is intended for educational purposes and hands-on training of antenna engineering and related applications. Particularly, the proposed antenna can be used for localization of passive RFID tags and DVB-T base stations.

This communication explores the use of a parallel-plate waveguide with a bed of metallic nails on its bottom plate with the aim to design all-metal radial-line slot array antennas (RLSAs). This kind of antennas would provide a highly-efficient directive radiation of circularly-polarized waves at millimeter-wave band, adopting a very simple power distribution scheme. Specifically, in this communication, the radial propagation of the fundamental mode within this pinned waveguide is explored and the coupling to the slot array is studied and modeled. This study will enable an efficient analysis and design of all-metal RLSAs.

The dielectric post-wall waveguide-based passive circuits are analyzed using a surrogate model represented by an attention-based recurrent neural network. The predicted results from this much simpler, trained model show a good agreement with those obtained by a corresponding full-wave computational electromagnetics analysis with a fully independent EM commercial software package.

An all-reflective, Schwarzschild objective design for corneal reflectometry is evaluated in the WR 3.4 (220-330 GHz) frequency band. The shadow created by the 60-mm diameter secondary mirror is sufficiently large to mount a standard, OCT system to enable concomitant data acquisition with both modalities while avoiding beam obscuration. The system was fed with a bottle beam comprised of a p = 0, ℓ = 4 Laguerre-Gaussian mode with a 12.5 mm beam waist radius for increased throughput. The 50 mm focal length system was checked with ray tracing and simulated with an in-house physical optics code using a PEC sphere as a test target. The coupling coefficient between the feed beam and scattered beam varied from 0.25 at 220 GHz to 0.36 at 330 GHz. While the system demonstrated a clear phase center < 1λ from the focal point, significant edge diffraction prevents the formation of a spherical phase front.

In this paper, a tunable passband Frequency Selective Surface (FSS) loaded with GaAs air-bridged Schottky diode is presented, appropriate for beam-steering and beam-scanning applications. The proposed structure allows the simultaneous control of both phase and magnitude of the electromagnetic waves transmitted by each unit cell through the introduction of tuning, which is achieved by the Schottky diode technology. The obtained tuning bandwidth lies within 7.04-9.42 GHz, with a central frequency of 40.5 GHz, the insertion loss has an average value around 1.47dB and the phase shift of the single-layer is equal to 101°. This FSS can be used as the building block for the development of higher-order tunable FSS filters or for transmitarrays able to electronically steer the direction of an incident beam and find applications in future 5G/6G and satellite communication systems. In this work, a multilayer tunable unit cell is reported which achieves a phase shift higher than 360°, with average insertion losses within 5-11dB and a 3dB bandwidth equal to 3.5GHz.

This paper proposes a low-profile and wideband monopole antenna. The low-profile property is achieved by capacitive and inductive loading to adjust the impedance of the antenna, and the wideband operation is achieved by designing the current paths on the top-loaded patch. The antenna has height of 0.07λL and stable omnidirectional radiation pattern in the operating band. The measured relative bandwidth is 69% and the gain in the operating band is higher than 2.2 dB.

The demand for higher data rates and stability in wireless communications is increasing steadily. The mmWave band offers higher bandwidths and therefore increased data rates compared to sub-6 GHz bands, however drawbacks such as limited range and vulnerability to blockage remain a challenge. In this paper, we take off-the-shelf mmWave devices in the 60GHz band and combine them with self-developed lenses. The results show a focused beam in one dimension, while offering full coverage in the other, resulting in increased ranges with constant, high data rates. This allows applications for industrial communication or wireless backhaul networks and use cases such as platooning with autonomous vehicles.

A wideband, monostatic, co-horizontally polarized (Co-HP) antenna system with omnidirectional radiation patterns for in-band full-duplex applications is presented. The proposed antenna consists of a printed four-element dipole array and two groups of parasitic strips for impedance bandwidth and omnidirectional performance enhancement. To achieve high isolation, the four ports of the proposed antenna are excited with two orthogonal phase modes for TX and RX using a well-designed beamforming network (BFN). The BFN is a six-port microstrip circuit, which consists of two 180º hybrid couplers, one 90º hybrid coupler, and a Wilkinson power divider. The measured TX/RX overlapping impedance bandwidth (IMBW) of the proposed STAR antenna system is from 4.71 to 6.2 GHz, and the TX/RX isolation is more than 40 dB from 4.81 to 5.88 GHz.

A broadband and high gain filtering antenna is designed by embedding two symmetrically oriented tapered slots. Broad bandwidth is achieved by using electromagnetically coupled stacked configuration. Tapered slots generate nulls in upper and lower bands of the antenna gain response. The designed antenna provides 35.6% BW with an average gain of 9.3 dBi. Null depth of lower and upper frequency bands are greater than 22.8 and 29.2 dB, respectively. The antenna provides a stable boresight pattern with cross and back radiation of better than 16 dB. The antenna is suitable for wireless communication in 2G, 3G, 4G-LTE and 5G applications.

Cell-free (CF) massive multiple-input multiple-output (MIMO) networks are an alternative to achieve a higher a more uniform signal-to-interference-plus-noise ratio (SINR) over a mobile coverage area. Most of the literature for these networks considers a star fronthaul topology. This topology may lead to a non-scalable complex and costly fronthaul network. Some works proposed serial interconnection among several access points (APs) to a Central Processing Unit (CPU) to solve this problem, an alternative we call cell-free with segmented fronthaul. However, there is a lack of studies investigating if this alternative is cost-saving. This work explores the technical-economic feasibility of cell-free with segmented fronthaul based on bus, star, ring, and tree topologies. Moreover, evaluations are made in terms of multiple levels of serialization, which are the number of APs connected serially. Results show that the best overall topology is tree-based with a low serialization level.

A low profile, triple band standard coverage, and multiple-input-multiple-output (MIMO) antenna system is proposed for mobile application in this work. The main objective of the study presented in the article is to reduce the coupling between the different access ports of the antennas to reduce the correlation between the signals received by them in a MIMO scheme. The MIMO antenna system consists of two Inverted F Antenna (IFA) multiband elements for 4G standard, covering different bands between 1720 and 2690 MHz, reused in 5G standards. This integrated MIMO antenna system is fabricated on a FR4 substrate with 𝛆r equal to 4.5. The dimensions of the board are equal to 130x60x1.54 mm3, which is a typical backplane of a mobile handset. The study includes two different distributions of the MIMO antennas in a handset, one of them with the antenna located in a co-polar configuration and the other in cross-polar configuration.

The design of linearly polarized, flexible, multi-band decagon ring monopole antenna is proposed. The decagon ring monopole antenna incorporates a decagon ring having a thickness of 5 mm encircling a chamfered patch to generate multiband linear polarized waves. These radiators are excited by coplanar waveguide (CPW) fed based technique to induce two resonances at 2.20 GHz and 4.10 GHz covering bandwidth requirement of Global System for Mobile (GSM) 1800, Long Term Evolution (LTE) 2300/2600, Fifth Generation (5G) and WLAN bands. The simulated outcomes confirm the -10 dB impedance bandwidth of 48.84% (1.64 - 2.70 GHz) and 43.01% (3.65 - 5.65 GHz) at resonating frequency of 2.20 GHz and 4.10 GHz, respectively. Further, the bending analysis validates that the impedance matching and radiation performance of decagon ring antenna have minimal impact on the operating bands.

This paper investigates the design and practical implementation of wideband antennas along with the application of cognitive radio. Three planar antennas, having omnidirectional radio pattern and limited size, are designed to respect the signal detection priorities in a shared environment: the frequency bands of GSM, LTE and Wi-Fi networks. They are fabricated on 1.6-mm-thick FR4 with permittivity εr = 4.4. The simulation and measurement results confirm their compliance with the requested specifications. Their performance in a spectrum sensing scenario are also evaluated according to a machine-learning based signal detection algorithm. A comparison between their performance in practice is realized by computing Receiver Operating Characteristics (ROC) curves.

A compact pattern reconfigurable antenna structure is proposed. The proposed antenna structure is composed of two shorted quarter-wave microstrip patch antennas placed side by side to share a common shorting plane. Therefore, the total length of the antenna is a half wavelength. Pattern reconfiguration is achieved by exciting two antennas with different phases and consequently steering the main beam. With such a compact antenna, beam steering up to 350 is demonstrated.

Antenna and low-noise amplifier (LNA) co-design is a promising method for increasing the sensitivity of millimeter-wave (mmWave) receiver systems. Co-design involves several individual steps which usually do not intersect with each other in one design flow, but this method combines all of them together and allows to obtain mutual benefits for all components. This paper gives an overview of several different mmWave engineering tasks like antennas and monolithic microwave integrated circuit (MMIC) design together with RF interconnection solutions like wirebonding, flip-chip and packaging technology. The suggestion of the mmWave receiver co-design for achieving minimum noise figure at low costs is also provided.

Microfluidically frequency reconfigurable and polarization reconfigurable probe-fed patch antennas are presented in this paper. For the frequency reconfigurable antenna, a frequency tuning bandwidth of 14% (4.35-4.5 GHz) can be achieved by continuous loading of liquid metal inside the additively manufactured microfluidic channels on top of patch slots. During the frequency reconfigurability, the bandwidth remains greater than 5%, the gain remains higher than 7.5 dBi and there is polarization consistency over the complete tuning range. For the second antenna, switching between left-hand and right-hand circular polarization is demonstrated by alternatively inserting or removing metallic ink inside 3D printed Polylactic Acid (PLA) channels. For both polarization states stable reflection coefficient with -10 dB S11 bandwidth of 9.6% (4.48-4.93 GHz) and 3-dB axial ratio bandwidth (ARBW) of 5.2% (4.48-4.72 GHz, are achieved.

We present the experimental validation of the self-healing property of Bessel-beams at W-band. The capacity of Bessel-beams to heal after an obstruction is validated experimentally by placing a circular metallic obstacle within the nondiffractive region of the generated Bessel-beam. In particular, the near-field radiated by a broadband launcher with and without obstacles is measured, and its profile is compared in both cases. It appears that the Bessel-beam profile after the obstacle is preserved. The results show the resilience of Bessel-beams to obstacles over a broad bandwidth and their robustness in near-field links with applications in wireless power transfer and near-field wireless communications.

In this paper, a flat lens antenna using Gap Waveguide (GW) technology is designed at V-band. A Groove Gap Waveguide (GGW) horn antenna is used to feed the metamaterial lens placed in a parallel plate waveguide (PPW), in order to achieve a plane wavefront in the direction of propagation. Both devices, the metalens and the GGW antenna, achieve excellent radiation results when combined together. Due to its fully metallic composition, the structure presents more robustness, lower loss, and adaptability to a flat surface. These features make it an apt solution for millimeter-wave applications.

In order to meet the growing demand for new services, airborne or satellite platforms must integrate more and more radio systems while the space available for the integration of these elements is increasingly reduced. Particularly, the use of ultra wideband (UWB) Radar, Electronic Warfare devices or wide band telecommunication systems increases the difficulty to share the allowed frequency band on a platform. Then, the introduction of a narrow forbidden band in these UWB structures is a challenge today. This narrow band can be used for localization, voice, internet, communications using for example another antenna located nearby on the platform, but also inside the UWB antenna itself building a Multifunction Antenna. Agile Radiating Matrix Antennas (ARMA) (Fig1) built with wide band pixels are a good candidate to perform this multi-functionality as shown in this paper.

A circularly polarized (CP)-reconfigurable rectangular dielectric resonator Antenna (RDRA) is proposed for mm-wave applications. By utilizing two photoconductive switches, the antenna can be switched to radiate either a linearly polarized (LP) field, left-hand CP (LHCP) field, or right-hand CP (RHCP) field. The structure requires a simple fabrication process. The simulated results demonstrate reconfigurable polarization characteristics with an impedance bandwidth of 31.8% for both LHCP and RHCP radiations as well as an impedance bandwidth of 9.5% for the LP radiation. This is achieved in conjunction with a maximum gain of 7 dBi. The axial ratio (AR) bandwidth is ~11% for both LHCP and RHCP radiations.

A highly reconfigurable dual band cavity structure for satellite communications at K/Ka band is proposed. The key of the presented structure lies on a compact dual stacked cavity system. By modifying the radius of each cavity and the dimensions of the feeding slot, both cavities have been matched at the center frequency of their respective band. Correctly enabling and phasing each input port allows to generate any desired polarization scheme. Cavity radius were carefully chosen to prevent any coupling of the K band cavity with the Ka band one. For demonstration purposes, this structure has been integrated with a Turrin horn antenna that operates as a multimode horn for the Ka band. Monomode operation at the lower band was ensured by limiting the horn aperture radius. In this configuration a directivity of 10.3/12.4dB in K/Ka band was achieved.

An electronically-reconfigurable leaky-wave antenna based on metasurfaces is designed and implemented. This innovative antenna consists of a multilayered structure with two (metasurface) impedance planes. The beam scanning at fixed frequency is achieved by electronically tuning the surface impedance of the lower plane using voltage-controlled varactor diodes. The rationale of this solution is that a variation in the impedance profile of the antenna in the direction transversal to propagation affects the phase velocity of the leaky wave and therefore the beam direction.

A low profile wideband circularly polarized reconfigurable metasurface antenna is proposed. The proposed antenna consists of a 3 × 4 rectangular metasurface (MTS) and a rotated coplanar waveguide feeding line (CPW). Four PIN diodes (D1, D2, D3 and D3) are utilized to realize circular polarization reconfigurability. The antenna could operate in left handed circular polarization (LHCP) and right handed circular polarization (RHCP) depending on the state of the diodes. The simulated results show an impedance bandwidth (IBW) of 16% and a 3-dB axial ratio band (ARBW) of about 13% in both RHCP and LHCP radiation modes, while the gain for both polarizations is higher than 6 dBi in the operating band.

We design and estimate the performance of a single-layer center-feed slotted waveguide antenna array. First, we optimize the matching waveguide, the feed waveguide, and the radiation waveguide based on finite-element-method (FEM) calculation. Perfect impedance matching condition is realized by optimizing the length width and height of the matching waveguide. As a result, we obtain > 800-MHz bandwidth for input port (with < -20 dB S11). Besides, we successfully design a 1×5 feed waveguide with an S11 of -19.9 dB at 38 GHz. The responding conductive wall strongly suppresses the reflection of each unit. In addition, we present the analysis of a radiation waveguide with ten pairs of slots and stairs. Finally, we compare the directive gain and the aperture efficiency between the 10×10 slots antenna arrays with designed feed waveguide and an ideally feeding condition.

Highly integrated systems in package with waveguide interfaces are of high interest recently. To investigate the connections between the integrated system and waveguide based antennas, an interconnect based on gap-waveguide technology is presented in this paper. The dispersion properties of gap-waveguide pin texture adopted by the interconnect is demonstrated. The simulated results show that the proposed interconnect has low loss and provides high isolation regardless the air gap variation. In addition, the performance degradation due to the misalignment between the blocks is checked and the simulated results show that the interconnect is robust in terms of insertion loss and isolation. As a result, the presented interconnect is able to ensure robust system level integrations while requiring non-galvanic contact.

This paper concerns the design of a beam steerable Leaky Wave Antenna (LWA) based on integrated electronic devices. The design uses a Half-mode Substrate Integrated Waveguide (HMSIW) where the short circuited wall (via holes) is modified to integrate Varactor diodes. Thanks to the behavior of these varactor diodes, the wave number and the phase shift of the propagating signal can be controlled. To narrow the beam in E plane, the HMSIW antenna is used as feeder of a horn like structure. This antenna allows to have a beam steering of 25° for a fixed center frequency in H plane and a 24° beamwidth in E plane.

We propose a concept to achieve continuous leakage from a slow-wave through a combination of wave tunneling and anti-reflection structures, and the result is a metal-free uniform leaky-wave antenna that is entirely composed of intrinsic silicon. This holds potential to realize terahertz-range radar and non-contact sensing applications with no Ohmic loss.

This paper presents two novel miniaturized substrate integrated waveguide (SIW) cavity backed slot antennas (CBSAs) with multiband and broadband characteristics. The first antenna combines the modified non-resonant rectangular slot with two pairs of symmetrically placed shorting pins and fed with tapered coplanar waveguide (CPW) to SIW transition for obtaining three resonances at 8.8, 12.25, and 14.35 GHz. The 10 dB return loss bandwidths (BWs) correspond to three resonances are 4.78, 3.11, and 1.82 % with peak realized gain of 6.41, 6.31, and 7.26 dBi respectively. Later for the second antenna, an indigenous method of splitting the SIW cavity is incorporated using shorting vias to obtain broadband impedance matching. Lower and high order modes (half TE110 and TE210) of the SIW cavity are coupled together to achieve broad BW with S11<10 dB from 12.34 14.54 GHz (16.4 %) and a flat gain > 6.4 dBi over the operating range.

A single fed, compact and circularly polarized patch antenna operating in three frequency bands is proposed in the present paper. This patch antenna uses a polarized ferrite substrate which therefore has the property of naturally generating circularly polarized waves. The modelling process of a compact antenna having dimensions of λ0/10×λ0/9.5×λ0/27 at 3 GHz and presenting three circularly polarized modes is exhibited. A prototype measurement has been carried out for an experimental validation of the simulated results.

In this work, we investigate the effect of polarization diversity for the higher-order space harmonics (HSH) of periodically-loaded leaky-wave antennas, i.e., TE10 and TE01. A hybrid form of nonradiative dielectric (NRD) waveguide and substrate integrated waveguide (SIW) is used to explore the inherent diversity feature for our antenna. The radiation properties of HSH in different passbands are examined where we investigate the behavior of scanning range variation of different HSH of n ϵ [-1, -2, -3, -4]. Furthermore, the effect of the unit-cell geometry on the propagation constant, and beam alignment of the TE10 and TE01 modes is studied and we show how the concept of HSH can be utilized for achieving a dually-polarized leaky-wave antenna (DP-LWA) with fixed beam operation. The proposed work is validated by showing an experimental prototype of DP-LWA in which a good agreement is achieved between the simulation, analysis, and measurement results.

In this work, a new microstrip circularly polarized leaky-wave antenna is presented for X-band applications. The design of the proposed leaky-wave antenna is inspired by the conventional 3 dB branch-line coupler. The geometry of the unit cell of the proposed leaky-wave antenna is realized by removing the two collinear feed lines of the branch-line coupler. The open stopband is eliminated by optimizing the geometry. The proposed leaky-wave antenna provides impedance bandwidth with |S 11 | < −10 dB between 8.2-11.1 GHz. The bandwidth corresponding to axial ratio < 3 dB is 9.4-10.3 GHz. The antenna radiates in the broadside at 9.9 GHz with 14.1 dBic gain.

A novel technique to design Fabry-Pérot antennas with non-homogeneous PRS is described. It uses a transmission line circuit model to efficiently obtain all necessary unit cell designs that satisfy the cavity resonance condition. This method allows an increase in directivity without reducing the bandwidth for a given footprint. Some design examples in the Ku-band are presented, showing the evolution from a simple single-layer PRS to a non-homogeneous two-layer one. The latter achieves an increase of about 3 dB in directivity while maintaining the bandwidth in electromagnetic simulations. This way, the gain-bandwidth product is improved from a value of 5 to almost 9, effectively raising the antenna efficiency.

A planar leaky-wave antenna (LWA) with flexible circular polarization (CP) characteristic is proposed in this paper, which is promising for satellite communication applications. A novel fan-blade shape slot is utilized to achieve left- or right-handed circular polarizations by manipulating the wave propagating directions in the waveguide. Moreover, a two-LWA array is further investigated to obtain dual CPs in both the backward and forward scanning. In addition, the proposed LWA overcomes the open stopband, which is a problem frequently plaguing LWAs. As a result, the proposed LWA scans continuously from backward to forward. An example LWA is designed in the Ka band using the substrate integrated waveguide (SIW) technique with coaxial connector feedings. The main radiation beam steers continuously from −45° to 45° in dual CPs when the operating frequency varies between 28 and 37.3 GHz. A prototype has been fabricated and tested to demonstrate the design idea and application scenario.

In this article, a reconfigurable waveguide antenna design with linear-polarized/Left-handed/right-hand circularly-polarized (LHCP/RHCP) modes in K/Ka-Band for a massive MIMO beamforming system based on active phased array is presented. Both the linear-polarized and dual LH/RH CP waveguide antennas provide wideband operation performance for K/Ka-Band, which are applicable for the antenna array in a beamforming system for different purposes and requirements in satellite communication applications. Both simulated results and some preliminary experimental results are presented for the demonstration.

A novel millimeter wave series-fed microstrip line antenna array is designed. The antenna array consists of stepped inverted-cone stub sections placed on both edges of the microstrip line at a guided wavelength spacing. The 5 strip stub sections can alter the surface current cancellation at each guided wavelength in an ideal microstrip line. By properly tuning the length and height difference of the strip stubs, the equivalent surface currents can be focused to the stubbed inverted-cone sections present on the microstrip line edges and results in an effective radiation. The fabricated antenna array has return loss better than 10 dB around 27.3 GHz. Peak realized gain of 10.1 dBi is achieved and measured side lobe levels are better than -15 dB. The proposed antenna array has a very good radiation pattern and low side lobe levels which makes it a suitable direction for future integrated millimeter wave antenna arrays.

Cooperative Diversity Systems are used in current generation networks for improving the reliability and the quality of service of wireless networks. Cooperative diversity techniques have been proposed offering significant values of diversity gain and increase the of system's availability. In this paper, the outage performance of a Selection Relaying cooperative system with two aerial regenerative relays is evaluated in terms of easily calculated integrals. Rician fading is assumed for the satellite to aerial relays, while shadowed Rician fading is assumed for the relays to destination links. Extended numerical results show the importance of the cooperative diversity systems and finally, the effect of different shadowing conditions on the performance of the cooperative diversity system is presented.

This paper presents outdoor radio channel measurements at 140 GHz using a spectrum analyzer-based channel sounder operational in the D-band, ranging from 110 to 170 GHz. We measure directional Line-of-Sight (LOS) path loss (PL) in a suburban environment for distances ranging from 2 m to 95 m, using an omnidirectional transmit antenna and directional receive antenna. Every 10 m, a full angular scan is performed by physically rotating the receive antenna in steps of 12 ◦, which corresponds to the antenna's half-power beamwidth. A floating-intercept PL model is created, resulting in a fitted intercept P L 0 at 1 m of 80.7 dB, and PL exponent n 1.9. The azimuthal angular spread varies between 7 ◦ and 45 ◦, with a mean angular spread of 19.7 ◦.

Orbital angular momentum (OAM) can provide an additional multiplexing degree in wireless communications. However, it suffers large propagation loss in the misalignment and rich-multipath scenarios. In this paper, the joint iterative power allocation and average phase compensation (IPA-APC) scheme is proposed to improve the performance of OAMMIMO in street scenarios. On the one hand, the average phase compensation scheme improves the channel capacity as well as the phase deviations caused by misalignment and multipath; on the other hand, compared with the optimal power allocation (OPA) scheme, the proposed iterative power allocation scheme reduces the running time of the algorithm and ensures the capacity performance. Simulation results verify the superiority of the proposed scheme.

The radio refractivity is a valuable parameter to model radio communication links and it is widely used in numerical weather prediction (NWP), since it is closely related to temperature and relative humidity. Recently, a method to estimate this parameter from radar phase measurements was proposed. However, the accuracy of the estimates largely depends on the calibration stage, which is based on measurements performed by ground-based weather stations. Due to the high cost of installing and maintaining an automatic weather station network, looking for alternative calibration procedures has become interesting for radar operators. This paper discuses the reliability and performance of a new calibration method based on the European Centre for Medium-range Weather Forecast (ECMWF) reanalysis data.

This paper presents the design of two in-line transitions operating in Q-band for radioastronomy or satellite applications. Both employ the WR-22 rectangular waveguide. The first transition involves as end-launcher a microstrip line, the second a coaxial cable. Focus of the works is to obtain a design which simplifies the geometrical configuration by keeping a reasonable compactness and without affecting the transversal space occupation, while ensuring a good matching (return loss higher 24 dB in both cases). The performance are evaluated in terms of scattering parameters.

TV White Spaces (TVWS) is an attractive technology for rural wireless broadband, because of the frequencies used and the available bandwidth. Some successful trial has been carried out in different countries, with promising results, although the business model is still confusing. Colombian pacific coast is a vast region of tropical rain forest, with disperse afro and indigenous communities, with a complex geography and lack of connectivity. In this work, we show simulations with different propagation models, which includes multiple diffractions, to estimate radio coverage for a TVWS system, intended to provide broadband service in the pacific region. At the moment of writing this paper, the network is in the pilot stage, to verify the simulations and adjust the models; therefore, we only show the simulation results and some very initial results with three operating sites and simulation results for one projected site.

In this paper we present a new line-of-sight probability model for the urban micro cellular deployment scenario. This study utilises a high resolution 3D model of central London to conduct large scale ray-tracing of direct propagation paths between neighbouring lamp posts. These serve as a representation of mmWave self-backhauling small cells such as 3GPP integrated access and backhaul nodes. The statistical properties of the propagation paths are assessed against recognised line-of-sight probability models as a function of the distance between transmitter and receiver. Contributions as outlined in this paper have application in analytical studies aiming to understand the statistical characteristics of unobstructed high frequency ‘access' links between microcell sites and end users as well as ‘transport' backhaul links between neighbouring microcell sites.

Internet of Animal Health Things is an upcoming domain in both professional and domestic fields related to animal welfare monitoring including dairy cows, racehorses and domestic dogs. Wireless Body Area Networks represent a large allotment in the realization of these applications. Characterization of the path loss between on-body nodes in various surroundings is required when deploying such network. In this paper, the path loss between various on-body transmitting sensors and an on-body receiver is investigated at 2.45 GHz. Simulations using the Finite-Difference Time-Domain method are performed using a representative, homogeneous canine model on which two half-wavelength dipoles are placed at short distance from the body of the dog. Several combinations of transmitter and receiver locations and orientations are explored and for each transmitter location, the orientation and receiver location resulting in minimal path loss is determined. All path loss results are fitted to a log-normal path loss model with path loss exponent n ranging from 2.7 to 3.5. A link budget is composed with the wireless technologies ZigBee. The battery lifetime for several modules is determined. The ZigBee device XB24CAPIT-001 assures 237 days without recharging when using a battery capacity of 5000 mAh with an awake time period of 25%.

In this paper, the path loss of the THz channel in motherboard desktop environment has been characterized and modeled by both statistical (mixture distributions) and deep learning (MLP) models. The performance of the two different model classes are compared and results show that mixture models captures the randomness of the channel by matching the PDF of measured path loss, which means that the statistical model can adapt to the changing environment. However, for the complex yet static motherboard desktop environment, the deep learning model outperforms the statistical models since it can also precisely describe the hidden patterns due to resonant modes and signal propagation in the static environment.

Time-reversal receive antenna shift keying (TR-RASK) technology, which effectively facilitates designing a simplified receiver. However, it limits the number of receive antennas to be a power of two and the diversity gain of receive diversity cannot be utilized since only one receive antenna is selected in each time instant to receive information bits. Based on minimizing the bit error rate (BER) criterion, the Euclidean-distance-based receive antenna selection (EDRAS) algorithm is proposed in this paper. However, the EDRAS algorithm determines the receive antenna subset by maximizing the minimum Euclidean distance over all possible transmitted signals, which acquires optimal BER performance but incurs high complexity. To address this issue, the autocorrelation-based receive antenna selection (ACRAS) algorithm is proposed to select the M rs =2 ⌊log 2(M r )⌋ receive antennas with the largest sum of the autocorrelation as receive antenna subset, achieving sub-optimal BER performance with a significant reduction in complexity. Simulation results verify that the proposed algorithms outperform the traditional scheme without receive antenna selection. Furthermore, the results also reveal that the EDRAS algorithm achieves optimal BER performance with enormous complexity, while the ACRAS algorithm attains the sub-optimal BER performance but offers a significant reduction in complexity.

This paper investigates material and scattering loss from a general two-port leaky-wave antenna (LWA) in transmit and receive modes using scattering parameters. It is demonstrated that the total material and scattering losses depend on the LWA orientation and whether the LWA is used as a transmitter or a receiver, leading to a different radio frequency (RF) environment in each scenario. First, full-wave simulations are used to demonstrate this behavior for a patch-to-horn configuration. Then the behavior is experimentally demonstrated for two-port LWAs in different orientations with respect to a horn antenna.

This paper outlines a hardware platform for half-duplex, real-time encrypted digital speech communication on 2.45 GHz. The platform is based on a STM32F415 MCU with a low power ADF7242 transceiver for wireless communication. The Advanced Encryption Standard (AES) Electronic Code Book encryption scheme is performed on the transmitted packets with symmetrically generated channel-based keys. Encryption keys of 128-bit are obtained, based on the unique reciprocal channel characteristics of the employed link. Key reconciliation is applied by means of a Hamming code and a cyclic redundancy check (CRC) to correct key mismatch. A multi-user system is introduced by splitting voice key distribution and speech communication into different abstraction layers. Measurements reveal a maximum communication range of 400 m without significant packet loss. A high key entropy of 0.94 bit is established with a packet rate of 167 packets/s and a key bit generation delay of four received signal strength (RSS) measurements.

Using a conical horn as a feed for a single offset-fed Compact Antenna Test Range (CATR) is described. Although such horn has larger variation of the phase centre with frequency and slightly different beamwidth in the E-plane and H-plane within the used field of view, as compared to a specially designed corrugated horn feed, good results were obtained for the measured amplitude and phase variations in the Quiet Zone at mm-band. Some details of application of conventional conical horns as CATR feeds are also explained.

In this contribution, a 3D-printed, cost-effective measurement system based on a roll-over-azimuth positioner is proposed. The antenna measurement system is designed for educational applications and quick prototype validations, and will help students become familiar with antenna measurement procedures and error characterization techniques. The presented measurement system has an open design, it is easy-to-deploy and its modular design allows to easily implement new functionalities. The system performs spherical acquisitions and can characterize medium and low directivity antennas at different distances. Measurements and error tests for the characterization of an X-band horn antenna are shown to validate the correct performance of the system.

The power available from Photoconductive Antennas (PCA) by exploiting pulsed Optical-to-THz up/down conversions was so far only sufficient for localized spectroscopy. This has been a bottle neck for the wider use of these type of sources in sensing. However, recently reproducible m-watt power sources in the THz spectrum have been demonstrated by the THz Sensing Group. This talk will address some of the difficulties that hindered the progress for many years. The most important were likely associated to wide band modelling of short Electromagnetic pulses in complex active passive environments. Also the difficulties in manufacturing and interpretation of the measurements will be addressed.

Real-time microwave and millimeter-wave imaging methods are the workhorse in applications ranging from synthetic aperture radar, which operates with far-field data, to nondestructive testing and medical imaging, which employ near-field measurements. Research in this field is intensifying due to the rapid expansion of the wireless technologies beyond communications and into imaging and sensing. This expansion is fuelled by the advances of on-chip millimeter-wave to sub-THz electronics and the envisioned integration of communication and sensing in the future (beyond-5G) wireless networks and devices. This paper is an attempt to explain, categorize, compare and contrast the real-time imaging methods and algorithms within a common mathematical framework so that this interdisciplinary subject is rendered more comprehensible and accessible to the wider research community.

Nondestructive measurements are often employed for characterizing electromagnetic materials, especially in non-laboratory environments. Nondestructive techniques are fairly well established for simple media (i.e., materials that are linear, isotropic, homogeneous and time-invariant). However, the past decade or two has seen considerable interest in materials that are non-linear, non-isotropic (e.g., hyperbolic and bianisotropic media), spatially varying & dispersive (e.g., wire media), time varying (e.g., spacetime metamaterials) and non-reciprocal (e.g., topological insulators). What types of nondestructive techniques can be utilized for these materials? What new theory must be developed and what new measurement devices need to be invoked? What are the future challenges of nondestructive material characterization? How has 3D printing shifted the paradigm of the meaning of nondestructive evaluation? This talk will provide an overview of modern nondestructive material measurement techniques and will address the many questions and challenges one encounters when dealing with nondestructive evaluation of contemporary materials.

The Thuringian Center of Innovation in Mobility (ThIMo) under the roof of the Technische Universität Ilmenau operates an automotive antenna measurement chamber VISTA, equipped with a multi-probe measurement system covering the frequency range from 70 MHz … 6 GHz including the sub-6-frequencies for 5G mobile radio. In this talk, several current application-oriented research topics are presented and illustrated with examples. These research topics include:

Fast car antenna measurements in the installed state with various boundary conditions beneath the car.

Extension to antenna measurements installed on other electrically large objects like locomotives.

Emulation of LTE and V2X links as well as automotive radar in virtual environment.

Characterization of small cell antennas with regard to their RF exposure to humans by using a hybrid measurement-numerical method.

In this paper we present the results of an experiment carried out to assess the signal level variability induced by propagation through fire. It extends preliminary results carried just for the 200 MHz - 400 MHz frequency band to de 200 MHz - 4 GHz frequency band. Results show that signal level variability increases with frequency, reaching values that are significantly higher than the ones we report previously. Such variation should be taken into account as an additional fade margin when planning radio networks that should be resilient to fire effects.

In this paper, we present the results of wave scatterer localization at 4.65 and 14.25 GHz in an outdoor-to-indoor scenario at a traditional office building in Finland. The localization is based on a single-bounce model of interaction with a scatterer to localize the sources of measured multipath components. The estimated scatterer locations were mapped to an aerial photograph of the site and classified according to their location. We found that approximately two thirds of paths originate from higher order interactions with the environment. In contrast, one third of paths can be attributed to single-bounce interactions, with interior walls of the building being twice as strong sources of single-bounces as walls outside both in terms of power and number of paths.

In this paper, we investigate the sensitivity of the software-defined radio USRP X310 with a TwinRX daughterboard to strong interferers. In a conducted test setup, the signal-to-interference-plus-noise ratio (SINR) is measured under the influence of a mock-up Long-Term Evolution (LTE) base station. The frequency of the interferer is varied to analyze the effects over a wide frequency band, whereby a distinction is made between signals inside and outside the intermediate frequency (IF) band. The former can cause clipping at the analog-to-digital converter (ADC), while the latter are to be suppressed in the analog part of the software-defined radio. Here, leakage and higher-order mixing products make the receiver sensitive to spurious frequencies, whereby the performance degradation is particularly noticeable near the first intermediate frequency (IF1) of 1.25 GHz. At this point, even an interference signal with -28 dBm PEP causes an SINR loss of 3 dB.

This paper presents results of a measurement campaign conducted to evaluate the impact of forest fires on radiowave propagation. A total mass of 3.4 kg of Pinus Pinaster needles was used as fuel heap and it was uniformly placed in a triangular shape bed, above a metallic table. The ignition sources were two wool yarns soaked in diesel, allocated in two sides of the triangle, with different incident angles, in order to generate two independent fire fronts that will suffer a junction after some seconds. The excess loss introduced by fire was evaluated for a 5 GHz bandwidth, from 3 to 8 GHz. A multipath analysis is also presented in order to detect the variations on signal level, for the dominant components during transmission.

The evolution in wireless communication systems aims to provide adequate parameters in terms of higher transmission rates and increased spectral efficiency. Physical layer functionalities such as MIMO can increase throughput and provide higher coverage/capacity relations. However, its performance is directly affected by radio channel characteristics defined in the radio channel matrix, as well as in the employed antenna spacing. In this work, the performance of a MIMO system operating within a 5G NR FR1 capable band is analyzed, by considering volumetric channel analysis in frequency/power as well as in time domain and the impact of variable antenna spacing. The results show a clear benefit in received power level as antenna spacing is increased from 1λ to 3λ in the case of a complex indoor scenario.

The possibility to achieve advanced beam contouring capabilities with single-bit dual-polarization reconfigurable intelligent surfaces (RISs) is addressed in this contribution with reference to their application in the Smart Electromagnetic Environment (SEE) framework. The discrete multi-scale RIS reconfiguration problem is firstly recast in terms of a phase-only inverse source one. The RIS discrete descriptors are then optimized through a customized System-by-Design (SbD) strategy. Preliminary numerical results are presented to illustrate the wave manipulation capabilities and efficiency enabled by the proposed strategy.

The analysis of the power pattern generated from a uniform linear array is here carried in the Quantum Computing (QC) framework. The formulation and the analysis method based on the quantum Fourier transform (QFT) algorithm and the values observable at the output of the quantum computation are presented. A preliminary proof-of-concept result is reported and analyzed to point out the peculiarities and the advantages of the proposed method.

This work proposes a novel unbalanced corporate-feed network antenna design with amplitude tapering of the radiated power to get a reduced sidelobe level. The phase imbalance of the asymmetric power dividers is compensated by integrated delay lines which maintain the aperture efficiency. The 10 dB beamwidth is reduced by 8.5% in E-plane and 10.2% in H-plane after the phase compensation. A 16×16 and a 32×32 array antenna have been designed for 230-290 GHz, i.e., a 23% fractional bandwidth. The 16×16 and 32×32 antenna's realized gain is between 29.4-32.1 dBi and 34.6-37.6 dBi, with sidelobe levels better than 21.2 dB and 20.5 dB, respectively. The design is optimized for being implemented by silicon micromachining. To the best of the author's knowledge, this is the first amplitude tapered corporate feed slot array antenna with delay lines for phase compensation that has been proposed in this frequency range with this wide operational bandwidth.

This work presents a technical analysis and a proposal of the payload architecture including a 5G antenna design. The analysis covers the comparison with terrestrial networks and satellites, and the frequency bands and service area limitation versus available power and payload technology onboard actual High-Altitude Platforms (HAP). For this, a review of the HAP system capacity and payload requirements is done. Furthermore, the definition of the payload architecture is based on actual and mature state of the art of the technologies and the antenna aperture has dual-band and dual-circular polarization operation capacity.

A high gain (20 dBi) Leaky-Wave Antenna (LWA) is presented at 26 GHz with beam steering capabilities (44°) for high data throughput in millimeter-wave (mm-wave) 5G systems. A tunable phase shifting High Impedance Surface (HIS) exhibiting low loss (<0.1 dB), is employed for the antenna's beam steering. A Piezo-Electric Actuator (PEA) is employed to electromechanically tune the HIS. The employed PEA exhibited fast (milliseconds) and continuous displacement variation of up to 500 µm. The LWA has been demonstrated by deploying it within a 5G testbed operating within the 26GHz band. It was observed that the channel performance can significantly be improved utilizing the beam steering capability of the antenna in the case when the line-of-sight (LOS) is blocked by an obstacle.

This paper presents a method for designing reconfigurable microwave devices based on substrate integrated waveguides (SIW) technology. The method involves forming walls from drill holes that can be filled with liquid metal to form vias. Furthermore, the proposed method is validated by designing and testing several reconfigurable radio frequency (RF) switches. The switches are intended to be used for reconfigurable antenna applications. The measured results for the proposed devices are in good agreement with the simulated results and they show wideband operating bandwidth with highly efficient performance. The proposed method will find application within a wide range of different reconfigurable microwave devices and circuits.

Smooth communication between people and machines plays an important role in the intelligent environments of the future, where the best sides of both people and machines are to be exploited in the name of efficiency and flexibility. This requires a functional human-machine interface that allows the necessary control actions but does not require any use of robot-specific devices. In this paper, we further introduce a passive ultra-high frequency (UHF) radio frequency identification (RFID)-based platform, which is an attractive solution for on-body interfaces, as it is passive and maintenance-free, does not require a line-of-sight to function, and has reading distances of several meters. The unique aspect of this study is the established fully textile-based battery-free touchpad for writing digits, which can be integrated into everyday clothing and worn on body. Further, the paper presents various use cases for the developed technology.

From the viewpoint of heat resistance and reduction of the influence of the surrounding environment, an antenna system which is configured a metal box with a slot including small transceivers and a power supply device has been put into practical use. In this study, a robust antenna consisting of a metal box with a slot and a folded dipole element is proposed and their operation mechanism is clarified. Based on this operation mechanism, miniaturization of the metal box and enhancement of operating bandwidth are realized. As a result, the width of the metal box could be reduced from 0.22λ0 to 0.03λ0 and the relative bandwidth is improved from 7.6% to 18.9%.

This paper presents a high gain wideband circularly polarized antenna. The antenna is a small single-element antenna that radiates over a wide frequency band (from 4.8 to 6 GHz), covering 5.2 GHz (Wi-Fi) and 5.8GHz (ISM).A metallic reflector is placed behind the ground plane. The proposed structure achieves a wide beamwidth which ensures a flat-top angular coverage from -50º to +50º throughout a high gain of a range from 4 to 8.1 dBi. As a result, that antenna is proposed as a rectifying antenna (rectenna), as it guarantees good rectification efficiency. The antenna can be utilized to harvest RF energy from Wi-Fi and ISM bands.

Massive multiple-input multiple output (MIMO) is among the potential technologies to meet the expected performance of future wireless communication systems. There are two configurations of massive MIMO deployment: centralized and distributed configurations, called Cm-MIMO and Dm-MIMO respectively. The second configuration is shown to be the best choice of massive MIMO deployment when the antenna arrays are properly arranged. In this paper, we present an experimental analysis of uplink Dm-MIMO performance in an indoor environment considering maximum ratio combining (MRC), zero forcing (ZF), and minimum square error (MMSE) combining methods. Performance evaluation has been carried out in terms of the spectral efficiency and the user fairness based on indoor channel measurements.

3D-printed breast phantoms have been used to evaluate methods in breast microwave sensing (BMS). These phantoms use 3D-printed shells from MRI images to hold liquids that mimic the dielectric properties of breast tissues. The MRI-derived shells allow the phantoms to mimic the morphology of in vivo tissues and the liquids mimic the microwave properties of the tissues. The use of low-permittivity 3D-printable plastics in the shells poses a potential challenge, as the plastics do not mimic the properties of breast tissues. This work quantitatively investigated the effects of eight plastic fibroglandular shells. The statistical analysis in this work indicated that three of the eight phantom shells did not produce significant reflections. These results indicate that, depending on the specific phantom shell design, the utility of 3D-printed phantoms may be limited by using low-permittivity plastics, and further examination of the role of plastics in 3D-printed phantoms should be performed.

The on-body path gain is investigated for four different link configurations. The height and width of the body torso is varied for each link configuration to determine the influence on the path gain. To prevent that waves propagate from one side of the body to the other, absorbers are positioned on the torso. It is found that the path gain (in decibels) appears to be linearly dependent on the torso height and width. A realistic smooth convex stomach is added to the model which is comprised of mainly straight and flat surfaces. The thickness of the stomach layer is varied and the impact on the path gain is studied. Ear-to-front pocket links are seen to be influenced by the stomach size, whereas there are no apparent impact on ear-to-back pocket links. The simulations are performed in HFSS.

Nowadays, the application of microwave imaging for breast cancer diagnosis has expanded as an alternative method to traditional mammography. In fact, the use of electromagnetic fields in the microwave range allows determining the dielectric contrast between healthy and malignant tissue for the detection of breast lesions. Special phantoms are used to evaluate the diagnostic capability of these devices. In this work, a prototype that replicates both the anatomy of the breast and its dielectric properties has been designed. A heterogeneous, multilayers, realistic phantom of the pathologic breast has been designed using cheap commercially available materials with low production costs. Furthermore, the preservation of the prototype without any means of degradation has been tested. All the samples have been electromagnetically characterized by means of an already presented open-ended coaxial probe.

In this paper, a quantitative evaluation of the skin impact on mm-wave imaging systems for breast cancer detection is presented. Different scenarios, considering both homogeneous (skin + fat) and heterogeneous (skin + fat + fibro glandular) breast, were evaluated in a frequency range from 26.5 to 40 GHz. To take into account the dielectric and propagation losses, together with the reflection at the interfaces, the simulated results for both planar and full- wave scenarios were compared. All simulations were performed by using the software Ansys HFSS. The link budget was evaluated considering several constraints, together with the possible improving factor due to the expected utilization of a multi-static radar configuration in the final system. Results show that a target up to 4 cm in fat under a 2-mm skin is reachable with a standard VNA, while a dedicated electronic is required in presence of fibro-glandular tissue.

This article presents, for the first time, the end-to-end transmission of physiological data from implanted antennas mimicking sensors to a cloud-enabled aggregator device using fat intra-body communication (fat-IBC). The experiment was performed on a live porcine model in full accordance with ethical standards. Measurement data from two different sensors were collected and sent through a fat-IBC network. The fat-IBC network consisted of three nodes, of which two used antennas implanted in the fat tissue of a live porcine model and one used an on-body antenna placed on the skin. The sensor data was forwarded via Bluetooth Low Energy to an Intel Health Application Platform device, which in turn forwarded the encrypted data to a web server. The experimental results demonstrate that the fat channel can be used in an end-to-end communication scheme, which could involve relaying of sensor data from an implanted device to an external web server.

An improved equiangular spiral antenna with circular polarization is proposed as the radiating element for a phased array antenna intended for new generation space launchers. The spiral has been designed in printed technology to achieve a low-profile configuration capable to be embedded in the launcher fuselage. The bidirectional radiation of the spiral is converted into unidirectional by introducing the antenna in a metallic cavity. Furthermore, an absorber ring is added inside to maintain the radiation characteristics of the antenna without increasing its size as well as to adjust the axial and impedance ratio produced by the cavity. The antenna has been simulated and fabricated to validate its performance. Besides the array will operate from 2.0 to 2.3 GHz, wideband results of the spiral antenna have been obtained. The antenna, with a diameter of 0.6 wavelengths at 2.0 GHz, provides a 52% relative bandwidth (2.0-3.4 GHz) with a pure circular polarization.

This paper presents a design of a horizontally polarized antenna array for a new DLR airborne Ka - band polarimetric interferometric synthetic aperture radar system with the maximum gain of 24 dB, low cross - polarization level of - 40 dB and a shaped radiation pattern with low sidelobe level in both azimuth and elevation planes below -18 dB. It has been designed using the slotted waveguide antenna (SWA) technology for the center frequency equal to 35.5 GHz. The transverse slots have been cut into the narrow waveguide wall, where the use of iris pairs placed inside enables the radiation. A suitable feeding network consisting of a conventionally H - plane T - junction power divider and a directional waveguide coupler has been also described. Based on theoretical principles, the antenna array as well as the corresponding power splitter have been developed and fabricated while meeting mechanical and electrical system demands. The measurement results of the manufactured prototype have been presented and a good agreement with requirements has been achieved.

This paper presents an updated version of a passively steer antenna. This kind of antenna uses liquid dielectric to provide a fixed main beam direction. This is achieved by utilizing the movement of a liquid dielectric, due to gravity. To improve the radiation efficiency and gain of the antenna, we had added a hemispherical container filled with liquid metal below the antenna. The container acts as a reflector. An antenna prototype has been proposed with a fundamental resonant band of 1.45-1.55 GHz. Additionally, the realized gain, radiation efficiency and total efficiency of the antenna has been improved, in comparison with the previously reported design.

This paper presents a design procedure for circularly polarized radial line patch array antennas that allows the steering of the main beam whereas the axial ratio is not drastically affected. This method is an extension of a previous publication, in which the radiated phase of each element was adjusted by rotation depending on its position in the lattice. This way, a partial sequential rotation is included. The used radial line patch array antenna is composed by double stacked patches as radiating elements. The design procedure allows to radiate with both circular polarizations at K-Band (19.7 - 20.2 GHz) for SATCOM. An axial ratio below 2.2 dB for a ±30º steering angle in the azimuth and the elevation plane is achieved, with a gain decay of 2.5 dB with respect to broadside. All the configurations exhibit a good behaviour in terms of efficiency, with values near to 90%.

This article presents the design and development of a switchable circular phased array antenna in reception for SATCOM polarization in frequencies from 17.7 GHz to 20.2 GHz. The design of the radiating element consists of a double patch with a hybrid coupler to generate polarization LHCP/RHCP. The Xphased RFIC chip provides the phases for the sequential rotation to improve the axial ratio and phases for beam steering, in addition to switching the two polarizations. This array is upgradable to larger arrays to provide higher gain for SATCOM applications. In this paper, we will present the design of the radiating element, the design of subarray 2x2 and the characterization of the MMIC chip separately for subsequent integration.

This paper proposes and evaluates a method for creating circular polarization using a linearly polarized patch antenna array tuned for 30.5 GHz and an anisotropic polarization converting superstrate fabricated by means of additive manufacturing. The simulated efficiency and far field performance of this antenna is evaluated, as well as its ease of design and manufacture. This takes the form of an analysis of measured results using the design for a copper etched linearly polarized array and 3D printed polylactic acid (PLA) polarization converting superstrate. This resulted in a highly directive antenna array, expressing directivity of 23.4 dBi and gain of 19.9 dBi. Good circular polarization was observed.

A dual-band and dual-circular polarization Frequency Selective Surface (FSS) is presented. The unit cell proposed for the FSS have an improvement with respect to the state of art employing stub tuned resonators. This element provides a much more efficient decomposition of the incident vector tilted with respect to the symmetry axes of the cell and so best axial ratio performance lower than 1dB is obtained. The bandwidth for such axial ratio performance is 18% at K band with one circular polarization, and 13.6% at Ka band for the orthogonal circular polarization. This design provides a low-profile antenna implementation and low-cost solution with a total thickness of about 1.2mm

In this work, an active frequency selective surface (FSS) is proposed for space applications in X and Ka bands. The FSS offers three reflection bands at 20 and 30 GHz (uplink and downlink frequencies of Ka-band satellites) and presents a switchable passband at 10 GHz. The unit cell of the FSS is made up of three metallic layers, and four PIN diodes on the bottom layer are used to control the switching between transmission and reflection in X band. The FSS performance has been studied through an equivalent circuit model. The proposed FSS supports dual polarization and shows a robust spectral response for incidence angles of up to 30º.

This paper presents original three-dimensional unit-cells allowing to synthesize polarization conversion when arranged in periodic arrays. The three-dimensional character of the structure allows to profit from enhanced flexibility in the design. The proposed topologies allow to control the dispersion of the cells in order to attain broadband operation. In addition, monolithic manufacturing employing only metal can be envisioned.

Frequency selective surfaces are often manufactured as standard printed circuit boards. The advantages of sophisticated design processes can only be exploited if very fine structures can be realized. This poses enormous challenges for the technology used.

In order to be able to realize the finest structures, the thickness of the metallization layer must not be too large in order to be able to maintain a technologically feasible aspect ratio between structure width and metallization thickness.

Quartz glass as a substrate with a structured silver metallization allows such an aspect ratio. In addition, quartz glass offers the further advantage of having a very low loss factor.

A frequency-selective surface with a quartz glass substrate and silver metallization was simulated, manufactured and measured. The fact that good reflectivity is achieved despite the low layer thickness of the metalization is also shown in calculations.

This paper presents a low-cost coded metallic metasurface (CMM) to manipulate electromagnetic waves with a 1-bit fully metallic meta-atoms. The proposed CMM provides polarization-independent transmission for any code sequence at a low cost with a lightweight structure. The concept is validated with four different CMMs, which were characterized through full-wave numerical analysis. Each CMM can split the boresight beam into symmetric multi-beams in directions predicted through analytical formulations. This investigation reveals the significant potentialities of CMM as a building block to design multi-beam antenna systems.

We hereby propose two new metamaterial-inspired substrate integrated waveguide (SIW) designs, based on complementary split-ring resonators (CSRRs). The first variation of the CSRR SIW is uniplanar, synthesized by grounded single-CSRRs. This version is characterized by a considerable ease-of-fabrication, due to its uniplanar form and simple resonator pattern. A broadside-coupled CSRR SIW is also proposed, with both complementary gaps facing in the outward direction. The broadside-coupled design features lower losses than the rest CSRR SIWs, as it may be fabricated on much thicker substrates, resulting in components with lower conductor losses and, consequently, lower total losses. Both waveguides are appealing alternatives as platforms for designing low-loss, fully-planar, easy-to-fabricate mmWave components, with the uniplanar version aiming at easier fabrication, whereas the BC-CSRR SIW is preferred, when loss minimization is of greater importance.

A single-feed miniaturized wideband circularly polarized (CP) antenna with metasurface is planned for L-band applications. The projected multilayered antenna comprises of a patch radiator with embedded ring-shaped slot and grounded-via, a stacked slit-slotted-circular patch, a metasurface with 5×5-unit cells, and a coaxial feeding probe. An antenna prototype at L-band exhibits -10-dB reflection coefficient(|S11|) bandwidth of 15.7% (1.488 GHz ̶ 1.742 GHz), 3-dB axial ratio(AR) bandwidth of 11.0% (1.50 GHz ̶ 1.675 GHz), and gain of 5.0dBic within the 3-dB AR-bandwidth with an overall size of 0.375λo×0.375λo×0.065λo at 1.5 GHz.

Many different applications of electromagnetic cloaking for wire antenna systems have been proposed in the literature in the last decades. The scattering engineering of the antenna has been made possible thanks to the use of thin and conformal metasurface wrapped around the radiating element. More recently, the cloaking functionality of the metasurface has been enriched by loading the conformal coat with electronic elements, allowing to conceive unprecedented configurations in antenna systems. Here, we aim at further expanding the degree of freedom in antenna design, by reporting new possibilities enabled by reconfigurable covering metasurface for tailoring not only the radiation and scattering characteristics of the antenna but also its electrical properties. These new potentialities introduced by metasurface coats may pave the way to a new class of wired antennas where the electrical and radiation characteristics are made reconfigurable by simply varying the covering metasurface properties.

This paper demonstrates the capability of locally resonant metamaterials (LRMs) for creating compact metallic waveguide E-and H-bends, which are simultaneously working as bandpass filters. For creating these bent meta-filters, we use composite pin-pipe waveguides (CPPWs), which are a type of LRMs made from resonant pins inserted in a rectangular waveguide. Similar to linear-shaped CPPWs, the subwavelength spatial dispersion in E-and H-bent CPPWs can nucleate a hybridization bandgap and subwavelength modes with custom frequency and bandwidth. To guarantee compatibility with standard waveguides and to improve the matching, we design subwavelength metamaterial ports. Finally, we build and test narrow and wideband H-bent CPPW filters, compatible with WR75 (10-15GHz) interfaces. Our measurements demonstrate the good performance of the small bent meta-filters as well as the customizability of the bandwidth. Our findings enable us to merge assembly components, such as bends, and filters in an ultra-small volume. It may find applications for reducing the size of waveguide networks with complex geometries in telecommunication and radar applications.

This paper shows in detail the 3D printing and electroplating process for a WR-28 rectangular waveguide. The characteristics of the printing process that must be taken into account to obtain the best possible print and to avoid problems that may arise are analyzed. Several studies are also carried out on the copper plating process using the electroplating method, changing the current applied to the piece, the amount of plating time and adding a copper deposition retardant additive that helps to reduce the roughness of the surfaces. In addition, possible errors that can lead to faulty electroplating are discussed.

In this work, the additive manufacturing technique of Laser Powder-Bed Fusion is evaluated to manufacture metallic-only antennas for single-piece and lightweight prototypes. The proposed technique enables the production of metallic antennas without the need to, first, manufacturing a dielectric structure, and then, the application of a coating procedure. To validate the technique, a horn array antenna operating at the mm-wave frequency range is designed. The prototype is produced in a single piece of aluminum, including the radiating elements and the feeding network. The prototype is matched at 34.5 GHz, showing a good agreement with simulations. The prototype is measured in an anechoic chamber, and measurements show a good agreement with simulations at the frequencies in which the antenna is matched. The results show that Laser Powder-Bed Fusion is a potential alternative to produce metallic-only solutions, reaching single-piece and lightweight prototypes

In this article, the design of a fully 3D-printed bull-eye dielectric leaky-wave antenna is presented. The antenna replaces the concentric metallic rings of a traditional bull-eye implementation with rings made with high-permittivity dielectric filaments. This introduces two extra degrees of freedom in the design, namely the permittivity of the rings and their height. The effect of these two new parameters in the antenna performance is studied. Simulation results show that the proposed antenna maintains the cylindrical leaky-wave mode behavior, generating a conical beam pattern depending on the operating frequency. Finally, the antenna was successfully 3D-printed using a low-cost 3D-printer and commercially available dielectric filaments with the required relative permittivity values.

In this paper, an antenna system based on a Luneburg lens associated to a conformal array is proposed for multiple beams applications in which the angular coverage sector is ensured by a grid of beams. A preliminary design is presented to evaluate the performance of such system, then the final design considering the manufacturing process by 3D printing is presented. The antenna prototype will be manufactured and tested.

The following contribution presents the design and manufacturing of a coplanar waveguide (CPW) fed horn antenna operating in the frequency range from 33 GHz to 67 GHz. The antenna is manufactured cost effective using stereolithography (SLA) and selective laser melting (SLM) and fed using a Coplanar Waveguide (CPW) on a low cost printed circuit board (PCB). This leads to a overall cost effective, low weight, flexible and scalable design, whose limitations concerning accuracy, reproducibility and resolution of the 3D Print are shown and compared in detail.

We provide an update on the Caltech Space Solar Power Project (SSPP). Our space power station employs a "sandwich" architecture where solar energy is collected on one side of a plate and coherent RF is transmitted out the other, eliminating the need for transport of large DC currents across the power station. Lightweight custom ICs synthesize, synchronize, and amplify RF signals to convert the DC power, and provide synchronous control of all RF sources to form a transmission phase array enabling wireless power transmission at a distance. We use highly flexible photovoltaics (PV), substrates for printed circuit boards, and either patch or pop-up antennas supported by a foldable and rollable carbon fiber structure to package a large (nominally 60m x 60m) multilayered structure into a relatively small cylindrical volume. In order to increase overall efficiency, we employ radio frequency (RF) transparent PV over the antenna layer on one side of the sandwich and PV on the other to allow the antennas to point at the earth almost continually while in a geosynchronous equatorial orbit. We also have explored using optically transparent antennas over the PV layer which opens options for the types of antennas we can use. We summarize our progress to date and briefly discuss our impending on-orbit demonstration payload.

The RF-DC conversion circuit measurement system that can determine the optimum microwave circuit with the input power and load resistance fixed was constructed. By measuring the diode operating impedance and microwave circuit impedance with the constructed system, it was found that both impedances are not complex conjugate. From the result and constructed measurement system, we showed the RF-DC conversion circuit design method for various input power and load resistance conditions.

In this work an effective solution at millimeterwave for real-time focusing via Frequency Diverse Arrays (FDAs) is proposed, to be exploited for intentional far-field Wireless Power Transfer (WPT) applications. A confined and precise spot where concentrate the power is obtained by circular concentric frequency diverse array (CCFDA). The system is conceived as a multi-layer structure with the top layer hosting the patches, the microstrip feeding network, located in the bottom layer, directly connected with the radiating elements through metallized via holes. The main drawback offered by the FDAs' family, i.e. the displacement in time of the main beam, is solved with the exploitation of the time-controlled FDA (TCFDA) technique. The system is theoretically developed and numerically demonstrated by the full-wave analysis of the realistic layout of a multi-layer, 32-element, circularly arranged FDA with a center frequency of 24 GHz. The simulated results of the realistic layout demonstrate that this solution offers unprecedented capabilities in terms of power focusing with respect to the state-of-the-art, capable of capillary transfer of energy in dedicated areas while preserving the rest of the environment.

Aiming to develop a lunar solar power satellite system, this study deals with the power transfer subsystem, specifically the microwave radiation and focusing. In order to reduce the spillover losses the radiation will be analyzed through the quasioptics framework.

For that purpose, a 27 GHz gaussian beam generated by a rectangular horn antenna was focused by a dielectric lens.

The design procedure for the components is presented here as well as the simulation results of just the horn antenna and the horn with the lens. A comparison of both results will be provided, with a discussion on the use of the dielectric lens for focusing the radiation.

In order to evaluate the transmitting antenna using the SPS demonstration test satellite, a phased array antenna mounted on a low earth orbit satellite is assumed as the demonstration satellite, and satellite signal is received by a terrestrial receiving station. In this paper, we examined the method of reproducing the antenna pattern on the ground. In addition to approximating the antenna pattern using the two-dimensional least squares method, we described the examination when there was a reception level deviation between each receiving station, and were able to obtain data useful for the evaluation.

A Space Solar Power System (SSPS) can generate electricity without excreting CO2 gas nor harmful debris. It could be valued in SDG programs. However, SSPS is a huge system working in space so that several key technologies must be innovated and verified in space. This paper first introduces the importance and configuration of SSPS. Antennas are crucial components for system design, and should be used in the never-experienced way, so that many challenges are required. Finally, current accomplishments relevant to antennas will be described.

In this paper, we analyse an antenna array fed with element-specific phase shifters and amplifiers. The elements of the array are mutually coupled and the operation of the amplifiers depend on the load impedance presented by the array. We derive a method for maximizing EIRP in a given direction and demonstrate the concept by simulations with 2x2 array fed with element-specific phase shifters and amplifiers at 2.5 GHz. Compared to the reference case, the optimization provides up to 0.7 dB improvement in EIRP in the -3 dB beam steering range.

This paper presents the experimental validation of a three-dipole array optimized for maximum gain. The complex excitation coefficients associated to the array are calculated using a synthesis procedure based on the array factor. A parasitic array architecture has been selected to implement the proposed antenna solution. The high gain reached (8.6 dBi for a ka of 1.4) shows the interest of the proposed optimization method. Furthermore, it was shown that this optimization method decreases the sensitivity to errors in the dipole excitation coefficients at the cost of a lower directivity compared to the superdirectivity.

This paper proposes a 2x2 array fed by a compact 2-D beamforming network (BFN) in a 5 metals-layer Rogers substrate. The BFN is composed of four interconnected 3dB/90o stripline couplers designed in the broadside coupled stripline structure in the lower (1-4) layers allowing an easy and compact design. The 2x2 patch antenna array designed in the upper (5) layer is connected to the BFN by probes generating four beams with unique directions on azimuth and elevation planes. The array inter-element distance is 0.5λ0. To validate the performance of the proposed structure, a prototype of a 2x2 patch array has been fabricated and measured. Simulated and measured four beams have been realized. An 8.85dBi highest simulated gain and a 5.97dBi highest measured gain are realized respectively in (θ=26o, Φ=55o) and (θ=30o, Φ=55o) directions when port 1 is excited. The size of the 2x2 array without feeding TML is 0.76 λ0×0.81λ0×0.04 λ0.

This paper presents the design of a radome corner support that offers mechanical stability and low reflections for 2, 3, 4, 5G technologies. This corner frame, which has a winged platen shape, is based on the multiple-layer A-sandwich radome design model. This type of radome design is known for reducing the reflections of incident waves, reducing the E-Field perturbations inside the radome. A radome is simulated with the proposed frame to validate the design, enclosing a +/-45 degrees polarization crossed dipole array antenna. Radiation pattern simulations of the antenna array alone and inside the radome are obtained at different frequencies and incidence angles. The results show that using the proposed model considerably reduces the perturbations in of antennas radiation pattern inside the radome, obtaining, in the worst case, a mean square error between the antenna alone and with the radome of 22.64.

This paper presents an overview on the recent advances on Compressive Processing methods as applied to phased arrays synthesis and analysis with main focus on (i) synthesis of sub-arrayed antenna arrays, (ii) failure detection in planar phased arrays, and (iii) antenna characterization. The novelty as well as the main advantages of the proposed methods with respect to conventional state-of-the-art approaches are discussed in the paper.

A Plane Wave Generator (PWG) is an array of elements with suitable complex excitation that approximates a plane wave condition at close distance within a Quite Zone (QZ). The StarWave system has been designed to enable transmit and receive testing of 5G devices in dual polarization, within a 380 mm diameter QZ. The testing is performed using up to seven individual PWG's generating plane wave conditions from different directions. Each PWG undergoes a production testing to verify the amplitude and phase dispersion of the array elements by the feeding network. As several individual PWG's are required, each with many array elements, the production testing becomes time consuming and impractical. In this paper, we report and experimentally validate a fast production testing procedure that allow to verify amplitude and phase conformance and to determine the QZ performance of a PWG from a quick Planar Near Field (PNF) scan of the aperture.

A novel compact antenna test range (CATR) design is presented in this study. Conventionally, the edges of the reflector are parallel to the chamber walls. Instead, a diamond-shape reflector (DSR) is proposed in this design. The reflector is rotated for 45 degrees, so the corners of DSR point to the walls (patent pending). This design suppresses the scattering from the absorbers on the walls, which improves quiet-zone (QZ) performance accordingly. The design has been realized and validated with QZ measurement. The validated CATR covers frequency from 4GHz to 95GHz, so it is suitable for both FR1 and FR2 in 5G and potentially for 6G mobile communication.

A dual-polarized, cavity-based antenna array with implemented edge-soldered transition technique is presented for 5G millimeter-wave applications. The working band of the proposed antenna is 26.5-29GHz. Full structure consists of two PCBs soldered together to achieve end-fire radiation pattern. A 4x1 array prototype supporting single polarization has been manufactured and measured. The measured reflection coefficient over the band is -12 dB, and with uniform amplitude distribution, a maximum gain of nearly 10 dBi is measured. The measured array exhibits a scanning potential up to 30 deg. The measured results have good agreement with the simulations.

This paper discusses methodology for characterizing basic power linearity parameters of software-defined radios. First, we introduce a highly automated testbed for 1-dB compression point (P1dB) and third-order input intercept point (IIP3). With this system, we have observed some surprising deviations from the expected slope of 3 dB/dB in the power response of the third order intermodulation distortion (IMD3). In response to this, we developed a measurement technique based on linear regression that accounts for the actual slope. A methodology study considers this technique in comparison with existing techniques for IIP3 measurements of spectrum monitoring receivers. In consideration for the increase in IM3 model complexity, we also propose an alternative parameter to simplify the quantitative evaluation of spectral regrowth near the receiver noise floor. We argue that this equivalence point provides a designer with more valuable information than an IIP3 point for spectrum monitoring applications.

Multiple-input-multiple-output over-the-air testing evaluates the multi-antenna wireless systems' performance in a controlled laboratory environment by emulating realistic real-world fading channel conditions. Spatial correlation is the key metric to character the accuracy of MIMO OTA testing system. Along with the evolution into 5G era, the MIMO OTA measurement setup complexity increase as well, especially for accurate implementation of three-dimensional channel model. Furthermore, extension of the two-dimensional multi-probe anechoic chamber (MPAC) method into full spherical three-dimensional MPAC is impractical due to cost consideration and setup complexity. In this paper, we present the use of a cost-effective single-probe anechoic chamber (SPAC) method for MIMO OTA testing and demonstrate that better spatial correlation accuracy can be achieved over implementation of the 3D spatial channel model as compared with MPAC. The development of such method can significantly reduce implementation cost to support wireless device R&D process. Both the theoretical derivation and simulation results are validated.

Industry standards for over-the-air testing of LTE MIMO devices have used multi-probe anechoic chamber based systems to evaluate device performance in a spatially static environment. The spatial distribution of clusters in the chosen channel models are fixed, and the only geometric variation relative to the device under test is accomplished by physically rotating the device in the generated test environment. For 5G FR1 testing, the CTIA MIMO OTA working group is developing a test plan based on the use of dynamic channel models that vary the spatial configuration as a function of time, and allowing the communication tester base station emulator to perform link adaptation, allowing the device to choose the best MIMO or SISO diversity mode and data rate for a given channel condition. This paper will discuss the design considerations associated with developing this new channel model and the related test system requirements.

Our developed system consists of an optical fiber link microwave transmitting system, an antenna-coupled-electrode electric-field sensor system for 28 GHz-band as a microwave receiving system, and a 6-axis vertically articulated robot with an arm length of 1 m. Our developed optical fiber link microwave transmitting system can transmit the microwave from 23 GHz to 33 GHz with more than -20 dBm output level. Our developed electric-field sensor can receive the microwave from 27 GHz to 30 GHz. In this paper, we show a measured near field radiation pattern for the WR-28 standard gain horn antenna using the system.

Over-the-air testing enables realistic verification of radio base stations with antenna panels. To conform with the requirements, most over-the-air measurements for uplink of 5G radio base stations are performed in fully anechoic chambers. In this work, the comparison between using the fully anechoic chamber and the reverberation chamber for in-band blocking testing is conducted on a 5G millimeter-wave radio unit. The use of the reverberation chamber can reduce the time and cost of the tests. Good agreement can be observed between the results obtained from the anechoic chamber and the reverberation chamber for the in-band blocking testing.

Calibration and validation of mm-wave transceiver arrays with respect to phase and amplitude of all elements is an essential part of production testing. Also afterwards during operation it may be necessary to update calibration coefficients. Here we present an algorithm based on channel symmetries, derive mathematically its expression, experimentally verify its results with respect to amplitude in a mm-wave testbed and compare the results to an extract model.

The purpose of this paper is to define a mathematical formulation for patch arrays Far Field (FF) distance allowing to calculate the FF distance from the array size (N×M), the operation frequency and substrate permittivity. It illustrates how the theoretical FF distance based on the antenna dimension and wavelength overestimate the practical FF distance by 5 times.

Despite the growing popularity of Long Range (LoRa) wide area networks (WANs), there is limited research on the antennas' influence on a node's connectivity. In this paper, the channel gain of an 868 MHz LoRa-Wan node in an urban environment is used to evaluate the performance of different antennas, as well as evaluate motion, elevation, and shadowing effects on the nodes connectivity. A dual-transmitter node with two tightly-coupled antennas is utilized to characterize the channel gain between the antenna-under-test, and multiple indoor and outdoor gateways over 1 km away, through the relative signal strength (RSS). It is demonstrated that using a broadband UWB-inspired monopole implemented on an inexpensive cardboard substrate, the channel gain can be improved over commercially available whip antennas.

We present a wireless and battery-free sensing system operating at the UHF band to measure domestic ac current ranging from 0 to 13 A in a power cable. The proposed sensing system uses two tag antennas operating at 868 MHz, each connected to a tuning circuit. The reactance of the tuning circuits varies as a function of the dc bias from a current transformer, causing a shift in the resonance frequency of the tag antennas. The Magnus S2 RFID transponder chip is used to compensate for differences in the applied reactance, and transmits the extent of the tuning capacitance parameter in the form of a 5-bit sensor code which can be correlated to the current drawn by an electrical load. Results indicate currents can be measured reliably over 0 to 12 A representing a significant improvement over a single diode version of the technology.

Mono-static radar cross-section (RCS) is estimated for a set of randomly distributed loaded thin dipoles. The RCS calculation is performed using two techniques based on the total backscattered field and the radar equation. Different dipole configurations and the effect of complex load impedances are studied in order to highlight the RCS distortion. Numerical Electromagnetics Code (NEC) simulator is used for the computations.

This paper presents measurements of chipless RFID radar landmarks designed for indoor localization applications at 80 GHz and 240 GHz by means of frequency modulated continuous wave (FMCW) radars. Compared to a vector network analyzer, these radars have the advantage of achieving the readout of a complex signal at a significantly lower cost and footprint. Even without a full calibration, the radars are able to successfully measure the complex backscattered response of the landmarks. This enables the use of FMCW radars as monostatic readers for indoor self-localization applications in highly dynamic and densely cluttered environments.

In this paper, a compact, geometrically simple, ultra-wide band, flexible and tri band antenna is proposed for IoT applications. The proposed antenna is designed on commercially available flexible substrate material Roger RT5880, having relative permittivity, loss tangent and thickness of 2.2, 0.0009 and 0.79 mm, respectively. The circular patch is loaded with rectangular stub in order to enhance bandwidth and return loss, afterward, the circular patch is divided in two parts to place a diode in order to achieve frequency reconfigurability. The simulation and analysis of proposed reconfigurable antenna was done using Higher Frequency Structural Simulator (HFSS). Furthermore, to demonstrate the potential of the proposed work it is compared with state-of-the-art works for similar applications.

In this paper, a hardware advancement for a microwave multi-static system for breast cancer detection is presented. In particular, we propose a metasurface-enhanced antenna capable of enhancing relevant "weak" signals back-scattered by a tumour-mimicking target inserted in a breast phantom. Furthermore, we simulate a radar-based approach in CST Microwave Studio and use our previously developed Huygens principle-based algorithm to produce images of the target. Our results indicate that the proposed metasurface-enhanced antenna can significantly improve target localization and decrease image artefacts.

This study presents the initial experimental validation of a mono-static microwave imaging system to monitor liver microwave thermal ablation. The system consists of a tank filled with a coupling medium in which a 3D-printed phantom mimicking the ablation region is embedded. A slot-loaded Vivaldi antenna is moved in front of the phantom along a linear path, measuring the S-parameters on a finite number of positions. Both simulation and measurement results are found to agree with each other. The differential signal of the microwave imaging system with and without the presence of the phantom is over -90 dB, which is above the detection capacity of commercial VNA. The experimental validation of the system paves the way for the design of a multi-static microwave imaging system.

We numerically assess the potential of microwave tomography (MWT) for the detection and dielectric properties estimation of axillary lymph nodes (ALNs), and we study the robustness of our system using prior information with varying levels of accuracy. We adopt a 2-dimensional MWT system with 8 antennas (0.5-2.5 GHz) placed around the axillary region. The reconstruction algorithm implements the distorted Born iterative method. We show that: (i) when accurate prior knowledge of the axillary tissues (fat and muscle) is available, our system successfully detects an ALN; (ii) +/- 30% error in the prior estimation of fat and muscle dielectric properties does not affect image quality; (iii) +/-7mm error in muscle position causes slight artifacts, while +/-14mm error in muscle position affects ALN detection. To the best of our knowledge, this is the first paper in the literature to study the impact of prior information accuracy on detecting an ALN using MWT.

Microwave radiations have been proven to be effective in biomedical applications, including brain stroke monitoring. However, microwave algorithms in these applications are computationally expensive with compute-intensive parts that are termed "kernels". To speed up the medical diagnosis, it is crucial to adopt new methodologies to accelerate the execution of these kernels by using specific hardware solutions. A recent trend in designing hardware accelerators is High Level Synthesis (HLS), which creates an implementation starting from a high-level description (C or C++) of an algorithm. In this paper, we first categorize the recurrent medical microwave techniques and kernels. Then, we propose efficient hardware accelerators for these kernels in programmable devices by using HLS. Several hardware optimization strategies are introduced and their impact on the overall performance is explored. We believe that the analysis of these kernels and their corresponding hardware acceleration techniques can be greatly beneficial to the biomedical microwave research community.

Microwave imaging has many applications in the biomedical area, and one of the most promising application is brain stroke detection. The full-wave 3D modeling of medical imaging scenarios requires significant computational resources due to the complex anthropomorphic phantoms and antenna systems. Hence, it is of paramount interest to simplify unnecessary details in numerical models, without sacrificing accuracy. Algorithms for reconstruction are based on scattering parameters and electric field in the domain of interest. Hence, by comparing the S-parameters of the original model and the simplified one, we can assess the quality of the simplification. Here, we propose the algorithm for computing the equivalent homogeneous phantom from a realistic human head model. In the qualitative algorithms, the equivalent phantom can be used for the reference model as the patient's head before the stroke onset. In quantitative algorithms, such model can be employed as the intelligent solution for initializing the iterative process.

This paper extends the validation of an innovative calibration framework for microwave imaging systems combining measured scattering parameters with numerically simulated ones. The aim is to improve the imaging operator accuracy by overcoming possible variations between the measurement system and its numerical model. Here, we investigate the possibility of reconstructing the transmission coefficients, measured at the antenna ports, employing a custom set of simulations where manufacturing tolerances are introduced. The experimental validation considers a microwave antenna array designed for brain imaging; each antenna is immersed in a brick of custom coupling medium whose dielectric properties variability is mainly analyzed. Further, the simulated dataset is provided by a high-fidelity full-wave electromagnetic tool coupled with a 3-D CAD model. This work presents an essential step forward in the whole calibration scheme, to then be able to estimate the electric field within the domain of interest, thus improve the imaging operator.

A novel, integrated microwave-ultrasound breast imaging system that requires minimal or no movement of the breast between scans has been developed. In this work, we present initial imaging results using a tissue-mimicking phantom, with experimental data obtained from the dual-mode system. The breast phantom is composed of four regions: skin, fat, fibroglandular and tumour, each with complex-valued permittivity and acoustic speed that approximate those of real breast tissue. Quantitative ultrasound imaging is performed using a ray-based sound-speed reconstruction algorithm. Prior information is extracted from the ultrasound image and incorporated into the microwave inversion algorithm. Although the resolution of the ultrasound imaging system itself is insufficient to detect the tumour, the low-resolution sound-speed reconstructions are used to improve tumour detection via microwave imaging. Resultant images with and without the ultrasound-derived prior are presented. Preliminary findings are indicative of the potential of ultrasound-derived prior information in enhancing microwave imaging of the breast.

In this study we measured the electrical conductivity of bovine liver. The measurements were performed at frequencies from 10 Hz to 10 kHz (N=5 frequencies) using a custom four-electrode probe and a galvanostat. We examined how the pressure applied between the probe and the tissue influenced the conductivity of the tissue. We performed measurements at N=10 different pressure levels by both increasing (forward direction) and decreasing (reverse direction) the pressure. We found that the conductivity of the tissue drops with pressure, regardless of the direction. However, we found that the decrease of conductivity with respect to applied pressure was small compared to other soft tissues (e.g. muscle tissue). The results from this study suggest that the dependence of conductivity on applied pressure should not have a significant impact on the design of medical devices which depend on accurate knowledge of the impedance provided that their target is the liver.

This paper presents the design, the realization, and the experimental assessment of a novel portable microwave scanner prototype for brain stroke monitoring. The device employs a 22-antenna-array, placed conformal to the upper head part, composed of compact, flexible, and custom-made antennas working at around 1GHz. The validation includes the monitoring of an experimentally emulated evolving hemorrhagic stroke. The progression of the medical condition is emulated via a non-static phantom (custom-shape balloon), derived from medical images, and a single-cavity 3-D anthropomorphic head phantom. The phantoms are filled with liquids mimicking the dielectric properties of the hemorrhage and the average brain tissues, respectively. The imaging-based follow-up is approached using a differential scheme that receives the scattering matrices, taken at two different instants, and exploits the distorted Born approximation to form the image in real-time. The results verify the capabilities of the system to assess the continuous evolution of the stroke.

The effectiveness of a hyperthermia treatment is strictly dependent on the ability to sharply control the administered heating in the region of interest. Different optimization routines have been implemented to focus the electromagnetic radiation of an array applicator on the tumor target, minimizing the risk of hotspots in the surrounding healthy tissues. This problem is usually tackled in the literature by means of global optimizations involving the specific absorption rate (SAR). In this paper, we analyze the possibility to use an alternating projections algorithm (APA) to optimize the power deposition on a tumor located near the larynx of a realistic numerical phantom. The comparison with a standard global optimization algorithm (particle swarm optimization) shows how the APA could provide a more pronounced hotspot suppression and faster computational times for a proper choice of the constraining power mask.

In-situ far-field phase pattern measurements of a prototype of the Square Kilometre Array known as Aperture Array Verification System 1.5 (AAVS1.5) are reported and discussed. Such phase patterns have been measured using a UAV as flying test source. This paper presents a preliminary analysis of discrepancies between the expected and the reconstructed phase patterns. These discrepancies are attributed to a position offset (with respect to the nominal position) common to all elements belonging to the same subarray. A method that estimates this position shift exploiting a combination of measurements and simulations is presented and applied. The resulting position shift could be due to both non-regularity (non-flatness) of the ground and installation errors.

The increasing popularity of Unmanned Aerial Systems (UAS) as a novel solution for antenna testing is introducing new outdoor diagnostic techniques. Thanks to their flexibility, measurements that are only possible with restrictions even in indoor measurement ranges are becoming possible. However, outdoor ranges introduce error sources due to the presence of a reflective environment. In this work, the use of UASs for the characterization of outdoor operation sites through the Voltage Standing Wave Ratio (VSWR) method is proposed. The flexibility of UASs is used to perform flights along the radial component of a sphere centered at an illuminating antenna, characterizing the reflectivity level through ripple analysis. The system is introduced, as is the theory related to the VSWR method and its application to outdoor measurements and, using it, a reflectivity map of a test site is calculated, enabling the detection of sources of reflectivity and the possibility to prevent them.

This paper focuses on developing a measurement method for analysing the quality of service of a three dimensional (3D) beyond 5G network. The study's aim is efficient and reliable testing method development for the industrial communications network with the unmanned aerial vehicle (UAV). 5G and beyond 5G networks are seen as having potential in industrial environments that need cost-efficient connectivity services to Industry 4.0-the fourth industrial revolution that aims to integrate cyber-physical systems, artificial intelligence, and Internet of things in industrial processes. The industrial environment consists of various vertical sectors (i.e. manufacturing, logistics) with numerous communications use cases and peremptory requirements in terms of availability, reliability, latency and safety. Industrial use cases such as autonomous surveillance UAVs and automated cranes demand reliable 3D communication services for their operation.

The Defence Research and Development Canada (DRDC) antenna measurement drone was used to evaluate the beamforming performance of the Ottawa experimental OTHR transmit antenna array. Optimal and phase-only beamformers were compared and various calibration approaches were used with the intent of maximizing power toward a target and minimizing power toward the auroral clutter. Phase-only beamforming gave 7.5 dB more power on target than optimal beamforming. Surprisingly, theoretical calibration appeared to give better results than experimental calibration, making the far-field calibration task significantly easier.

A numerical investigation about the optimal way to acquire Near-Field (NF) samples to determine the Far-Field (FF) pattern of an Antenna Under Test (AUT) is performed, where the samples are supposed to be acquired with a robotic arm or an Unmanned Aerial Vehicle (UAV). The probe movement unit is modelled as a device that can move with constant velocity along paths with bounded curvature. Within this framework, some numerical experiments are performed and the results compared in term of FF accuracy obtained with different paths of similar length.

In this work, we investigate the significance of position accuracy for unmanned aerial vehicle (UAV) during millimeter-wave (mmWave) channel measurements. The studies are performed at 28 and 60 GHz frequencies. First, we study the effect of the error in the positioning on the 3GPP channel models. Second, we present ray tracing simulations performed in urban environment. We verify that the horizontal/vertical accuracy of ±0.5/0.8 meters may be enough to get reliable data. It should be noted that better accuracy can still improve the results but will require more effort to achieve. In addition, it is confirmed that more severe effect will be visible on the path loss values, while other parameters are not affected as strongly for the LOS case. Power angular delay profile might be severely affected for the NLOS if the positioning error is large, however, defined accuracy values are enough to get realistic channel estimation.

Fully coherent unmanned aerial vehicle (UAV)-based near-field measurements of the S67 parabolic ground station antenna in Weilheim, Germany at 2.063 92GHz are presented. The utilized measurement setup involves a vector network analyzer (VNA), radio frequency optical fiber connections, a laser tracking device (LT), and a specially designed light-weight dual-polarized Vivaldi antenna. The measurement data has been collected on a quasi-planar measurement surface in front of the reflector and the far-field patterns are obtained by field transformation from the irregular near-field data. Despite the complexity of this outdoor measurement setup with full exposure to varying weather conditions and the influence of the UAV on the near-field probe antenna, the far-field results show remarkable agreement with satellite based far-field measurement data.

Phased array antenna is increasingly applied for satellite communication on the move terminals. Phased array antenna radiation pattern has been evaluated in the conventional facilities by measuring the entire sphere or plane from different steering angles. As the demand of satellite communication is growing, it is required to make the terminal antenna evaluation process faster than ever before. In this paper, new framework to partially evaluate phased array antenna characteristics is proposed by introducing dynamical UAV system with RF payload. The process of the evaluation can be accelerated by focusing on a few key aspects such as transition of the multiple beam peaks gain and their directions as steering angle is changed. UAVs can track multiple beams autonomously thanks to the trained system by reinforcement learning algorithm.

Near-field antenna measurements can be efficiently performed with Unmanned Aerial Vehicles (UAVs). An accurate knowledge of the position and timing is needed, and can be provided by Real-Time Kinematic (RTK) positioning systems using Global Navigation Satellite System (GNSS) signals.

In this paper, we assess the accuracy of a GNSS RTK positioning system with a laser tracker that provides ranging measurements with a precision of up to 16µm. The measurement results show that the positioning solutions of the GNSS RTK system and of the Laser tracker agree within a few centimeters. This accuracy is also correctly indicated by the self-assessment of the RTK system.

This paper concentrates on studying 4G/5G mobile network technologies applied to smart city Unmanned Aerial Vehicle (UAV) services. It reviews the state of the 5G technology and introduces proposed UAV services for smart cities. The paper describes our drone measurement platform and the results of the conducted communication QoS measurements in urban environment. The results indicated that 5G is more sensitive to altitude changes than 4G network and this should be considered in the future mobile network planning.

Four years of scintillation measurements at very low elevation angles at Kjeller, Norway are analyzed and compared with the ITU-R model. One year is at Ka band with an elevation angle of 3º, and three years are of simultaneous measurements at Ka and X band with an elevation angle of 4.2º. The measured scintillation is highly asymmetrical with more than 40 dB fades recorded at Ka band. In agreement with previous results, the scintillation spectra for low elevation angles have a low corner frequency. Compared with the ITU-R model, the measurements highlight issues with uncertainty of input parameters, as well as accuracy of the deep-fading part of the model. The model predicts the measured scintillation well for high percentages of the time, but poorly for low percentages of the time. The deep-fading part of the model significantly overestimates fades at X band, highlighting a previously observed issue with frequency scaling.

Scintillation is a phenomenon that affects microwave links and is still poorly modeled. Results of long-term measurements -5 years with almost 100% data availability- performed simultaneously from the same location at two different frequencies (Ka and Q-bands) in a converging link are presented here. The similarity of the time series of scintillation intensity in the two bands is commented. The variability of the standard deviation of the scintillation with the time of day on an annual basis and also on a monthly basis is analyzed. Annual cumulative distributions are also presented and explored. The performance of some available models in the literature for scintillation amplitude is evaluated using locally measured meteorological data. The ITU model seems to slightly over predict the experimental results.

Tropospheric scintillation of signal is caused by rapid fluctuation of refractive index due to random changes of humidity, pressure, and temperature in clear air, clouds and precipitation particles. The refractive index is continuously changing along the propagation path, causing random fades and enhancements in the signal level. In the system design phase, the prediction of long-term statistical distributions of signal fades and enhancements are needed. Long periods of measurement data are needed to characterize and model the scintillation statistics. In this paper, annual, seasonal and monthly statistical analyses of the scintillation fades based on the three-year beacon measurements of the Alphasat satellite at 19.7 GHz and 39.4 GHz in Ljubljana, Slovenia, are presented. The annual curves are also compared with the scintillation fades predicted by the ITU-R P.618-13 model.

The weather-forecast based Radio Meteorological Operation Planner (RadioMetOP) model for the dynamical satellite link-budget design and its operative application to the BepiColombo ESA deep-space mission to Mercury are described. BepiColombo is the first European deep-space mission adopting Ka-band for the downlink of telemetry data. At such high frequency, classical link budget techniques based on static climatological statistics for the characterization of the atmospheric channel are not suitable. RadioMetOP provides a dynamical model exploiting weather forecasts on the specific satellite transmission period coupled with a radiopropagation model for the prediction of atmospheric attenuation. This allows an improvement in the data throughput compared to classical link budget design techniques. For the first time, RadioMetOP model will be operationally adopted and tested thanks to the collaboration with ESA for the BepiColombo mission. RadioMetOP model can be extended to become multi-mission, multi-site, and multi-frequency in order to be adopted for future satellite missions.

The comparison of 1-min rainfall rate measurements with predictions from ITU-R P.837-7, in different regions and climates is useful for testing and improves its accuracy. We report for the first time, results of a comparative study in Bolivia. The ITU-R P.837-7 method is tested against precipitation data gathered in 3 pluviometric stations, with 15-min time resolution. EXCELL RCS model is used for downconverting statistics to 1-min integration time. A slight correction on this model was needed for 2 stations located at high altitudes. Error analysis for each station shows that ITU-R P.837-7, using monthly mean total rainfall as input, has good performance. In absence of this information, predictions based on digital maps produce an increase of error metrics. EXCELL RCS model has demonstrated being a tool helping to overcome the lack of 1-min rainfall measurements. We believe our findings contributes to rainfall modelling for propagation purposes in South America.

The formulation of characteristic modes using a transition matrix is independent of the associated computational tools. This enables frequency-domain solvers such as the finite element method to complement classical method-of-moment-based formulations in characteristic mode analysis. Here, it is shown that standard finite element solvers can be used to determine characteristic modes for heterogeneous objects, exemplified by a dielectric coated metallic cylinder.

Non-linear Partial Least-Squares based Polynomial Chaos Expansions (NLPLS-based PCE) has recently been shown to allow yield analysis for high-dimensional problems. A comparison of coefficient calculation techniques in the PCE step of the algorithm is done to determine the appropriate technique for generalized antenna problems. An NLPLS-based PCE surrogate of an 8-variable dual-band patch antenna and a 37-variable diplexer is constructed using Ordinary Least-Squares (OLS), Least Angle Regression (LAR), and Orthogonal Matching Pursuit (OMP). LAR and OMP provided a more stable solution when compared to OLS for both the dual-band patch antenna and diplexer, with OMP outperforming LAR for the 8-variable dualband patch solution. The choice of an appropriate coefficient calculation method is thus determined to have a significant influence on the effectiveness of NLPLS-based PCE.

This communication introduces a methodology to analyze infinite arrays of antennas by a fast post processing of the Generalized Scattering Matrix of a single, non-coupled, element, in terms of spherical modes. First, the Generalized Scattering Matrix is computed with the Finite Element Method only once whatever the array lattice or scan angle. Next, the active reflection coefficient and the embedded radiation pattern of the infinite array is quickly calculated for any lattice or scan angle thanks to an efficient computation of lattice sums of spherical harmonics.

This paper presents an improvement to an iterative domain decomposition method for the analysis of large antenna arrays. The method considered, is the iterative domain Green's function method (DGFM), with extended local MoM domains. It yields an approximate solution to the global method of moments (MoM) problem via the solution of a succession of local sub-problems. The local sub-problems are obtained by rigorously formulating the MoM on local domains, with all array elements outside these local domains modelled using an improved far-current approximation which is a hybridisation of the DGFM and standard Jacobi approximations. Numerical results demonstrate that this new far-current approximation improves the convergence rate of the iterative DGFM-MoM. The improved formulation retains the main benefit of the DGFM, which is that it is well-suited to parallelisation.

This paper studies the cylindrical Laminated Resonator Antenna (LRA) fed by the coaxial probe theoretically. A theoretical model is proposed to analyze the omnidirectional radiation characteristics of the cylindrical LRA. Based on the waveguide excitation theory, analytical expressions for inner fields, modal coefficients, radiation pattern, directivity, radiation efficiency and gain have been developed. For verification, a cylindrical LRA in the dominant TM011 mode operation is simulated. Acceptable agreements among the calculated and simulated results are achieved and omnidirectional radiation patterns are observed. The proposed theoretical model provides physical insight into the cylindrical LRA in omnidirectional mode operation, which can be applied to predict the performances of LRAs and to instruct the design of LRAs.

The dynamic control of the phase in reflectarray antennas (RA) with dual-polarization using liquid crystal (LC) technology is a very challenging task. The selected reflecting elements must have an almost independent response for each orthogonal polarization, with 360o of phase range, smooth linear variation of the phase, minimizing the losses and avoiding the coupling between polarizations. This contribution proposes a multi-resonant element made of two sets of dipoles, with orthogonal orientation to be used in W-band (100 GHz), using liquid crystal for reconfiguring the phase of the reflected, wave with an independent response for each polarization.

In this work, the procedure for the design of innovative reflectarray (RA) antennas able to radiate multiple Orbital Angular Momentum (OAM) modes is introduced. Extending the concepts at the base of multifocal lenses, the RA is designed in such a way that, depending on the direction of arrival of the incident field, it radiates a broadside beam carrying an OAM with different index. As a proof of concept, a circular RA with diameter D = 20lambda at the the frequency f0 = 30 GHz, able to radiate OAMs with l = 2 and l = 4 has been designed. The results obtained through its full-wave simulation, confirm the effectiveness of the proposed solution.

Reflective linear-to-circular polarization (LP-to-CP) converters are desired for satellite communication applications to reduce the complexity of the antenna system and the number of the required apertures in single-feed-per-beam configurations. Moreover, wideband operation and angular stability are important polarizer attributes in these applications. Here, for the first time, we use a machine-learning technique employing a generative adversarial network (GAN) to systematically and efficiently explore and exploit the solution space of single-layer structures for this problem. By using a GAN to optimize the shape of the polarizing element, superior performance in terms of overlapping axial ratio bandwidth for normal and oblique incidence of 30 ◦ compared to the previously studied designs is achieved.

Design and simulation results of a polarisation selective reflectarray in Ka band are presented. The reflectarray is part of a dual-offset antenna system for a high-resolution and wide-swath Synthetic Aperture Radar (SAR) instrument that operates in both a high-resolution mode with a directive beam in one polarisation, and a low-resolution mode with a broader beam in the orthogonal polarisation. Fed by orthogonal modes, a sectoral horn illuminates the reflectarray antenna with different beam widths for the two operational SAR modes. Radiation patterns of the feed and reflectarray antenna system are presented.

This contribution proposes the use of passive reflectarray panels as an efficient and low-cost technology to enhance millimeter-wave coverage in 5G indoor scenarios. A dual-polarized shaped-beam reflectarray has been designed to produce a highly broadened beam in the azimuth plane (half-power beamwidth of 13º) with a deviation of 45º with respect to broadside. A single-layer reflectarray cell has been used to obtain an angularly-stable phase response at the 28 GHz band with independent phase control in each linear polarization. The phase shift distribution on the reflectarray panel has been computed by a phase-only pattern synthesis, considering the beam specifications of the indoor scenario. The reflectarray panel shows stable gain and side-lobe levels, and very low cross-polarization in a 1 GHz band (from 27.3 to 28.3 GHz).

In this work, a novel approach to define masks in near-field syntheses is presented. This technique improves the convergence of the algorithm when dealing with complex scenarios and uniform field requirement. First, the methodology of the synthesis process is fully described. Second, an example is presented to better understand the concept. The technique is combined with the generalized Intersection Approach for near-field, and a transmissive spatially-fed array is synthesized. The synthesis aims to reach uniform field distribution in a large and complex-shape area. A major challenge is to overcome the issues presented because of the electromagnetic propagation. The strategy followed in the synthesis reaches the desired uniform field distribution, reducing the starting ripple from more than 30 dB to almost 5 dB in an area larger than 14 meters.

A 1-bit reconfigurable reflectarray antenna using PIN diodes is presented for 71-76GHz millimeter-wave communication applications. Based on the method of polarization conversion, the 0◦/180◦ element phase is accurately realized by loading 2 PINs on each element in order to overcome the unstable parameters of PIN in E-band. A square aperture reflectarray consisting of 16×16 elements is then designed and analyzed. Full wave simulation results demonstrate that the gain of the antenna is 17.1dBi, and the beam scanning angle can cover 45◦.

System-by-Design (SbD) has recently emerged as a powerful and efficient approach in reflectarray antenna (RA) synthesis and optimization. The features/properties of SbD (e.g., its flexibility and natural capability to handle complex multi-scale task-oriented problems) and the intrinsic challenges associated to advanced RA synthesis have motivated a great interest in developing and applying SbD-based approaches in reflectarray engineering. Within this framework, the objective of this contribution is to present a review of the current and most recent advances of SbD formulations as applied to reflectarray design developed at the ELEDIA Research Center. Towards this end, the customization of the SbD loop to the RA synthesis problem is illustrated, and the integration of advanced micro-scale modeling techniques based on learning-by-example strategies with macro-scale task-oriented optimization strategies is discussed. Current challenges and trends in the application of SbD to the solution of advanced RA design problems are remarked, as well.

This contribution describes the design process of a dual-band polarizer reflectarray antenna in K/Ka-bands for CubeSat applications. The reflectarray has been designed to focus a high-gain beam at 19.7 and 29.5 GHz while converting the incident polarization from dual-linear into dual-circular polarization. The independent operation at two separate frequency bands is accomplished by a dual-layer reflectarray cell. The flat surface of the reflectarray simplifies the mounting of the antenna on the small spacecraft and the linear-to-circular polarization conversion allows to reduce the number of components in the feed chain, also reducing the cost and complexity of the antenna subsystem.

This work aims to investigate the limitations and possible solutions in designing highly tilted radiation pattern reflectarrays working in double circular polarization and fed by an onset single primary source. To this extent, three single-layer monolithic reflectarrays, producing a pencil beam at increasing radiation angles with high X-polarization discrimination (XPD) have been designed and analyzed. A direct optimization technique shows that an XPD=20 dB can be attained for radiation patterns pointing at sixty degrees, at the cost of co-polarised directivity degradation. An analysis of the target aperture fields, obtained through backscattering techniques, shows that an amplitude modulation on the aperture field components is necessary to obtain highly tilted radiation patterns with high XPD. Since reflectarray cells are not able to produce such amplitude components unbalance, an elliptically polarized source is considered, producing an incident field components amplitude unbalance that results in a radical reduction of the X-polarization levels.

This paper proposes a decoupling technology of compact decoupling wall combining split resonant ring (SSR) and grid metal stubs for a two-element wideband and dual-polarized antenna array. By integrating the metal grid stubs and SSR on the same substrate to form a compact decoupling wall. The four identical compact decoupling walls are installed around the antenna array element to reduce the mutual coupling between the antenna array elements. The dimensions of the SRR and the grid metal stubs are optimized to achieve the best decoupling level for the array. The results demonstrate that the compact decoupling wall has the capacity to reduce the mutual coupling of the array from -13.8 dB to lower than -24 dB within 4.25 GHz - 4.98 GHz. In contrast, it almost does not affect the radiation characteristic of the array.

A systematic methodology is introduced for the design of broadband microstrip antennas (MAs) made of two stacked patches that are fed by an aperture coupled to an open-ended microstrip line. The MAs are modelled by an equivalent circuit (EC) consisting of two LC parallel resonators that are capacitively coupled, the EC being connected to the microstrip line by a LC series resonator that models the feeding. The circuit parameters are de-embedded from Momentum antenna simulations by using a novel technique based on the total least squares method. The EC of the MAs is adjusted as a second order filter with quasi-Chebyshev response, and the filter bandwidth is maximized so as to achieve broadband MAs. One MA has been designed with a center frequency of 5.57 GHz and a bandwidth larger than 30%. The MA has been fabricated and measured, and good agreement has been found between simulations and measurements.

We present the design of a wideband wide-scanning phased array for mobile communications. The array elements are connected slots in a dual-polarization configuration, radiating in the presence of a superstrate made of artificial dielectric layers (ADLs). Two interchangeable ADL superstrates have been designed, the former one allowing narrowband operation from 6 to 8 GHz (NB), and the latter one operating over a wide band between 2.3 and 8 GHz (WB). The performance is analyzed in terms of unit cell simulations, including the feeding structure. The NB design achieves an active reflection coefficient lower than -10 dB for scanning up to 60 degrees in all azimuthal planes. The WB design exhibits an active reflection coefficient lower than -6 dB for the same scan range. The designed feeding networks, based on microstrips and striplines for the two polarizations, respectively, are also presented.

This paper presents an ultra-wideband (UWB) compact size printed monopole antenna with improved gain and efficiency. This broadband printed monopole antenna contains a cup-shaped radiator fed by a coplanar waveguide (CPW) technique. The designed UWB antenna is fabricated on a less-priced FR-4 substrate with relative permittivity of 4.3, loss tangent of 0.025, and a standard height of 1.6 mm, sized at 31.68 mm × 23.76 mm × 1.6 mm suitable for wireless communication system. The designed UWB antenna works with maximum gain (peak gain of 4.1 dB) across the whole UWB spectrum 3-11 GHz. The S11 results are simulated and measured and the results are debated in detail.

A methodology based on the design of antennas with the use of unit cells is presented in this paper. The methodology is applied to a previously presented 4-port cavity-backed MIMO antenna which is split in 4 identical unit cells due to its symmetric geometry. In the presented study, it is demonstrated that with the analysis of only the unit cell of the antenna the behaviour of the whole design can be predicted. Thanks to this methodology, the design of complex N-port antennas is simplified to the analysis of a unit cell and opens a new via for designing symmetric N-port antennas for massive MIMO applications.

A dual frequency (433 MHz and 2.45 GHz) circularly polarized MIMO rectenna with dual-branch rectifiers and a common power management unit is presented. For the lower frequency a dual-layer, four-element, monopole antenna array is implemented. The four monopoles are oriented along the perimeter of a square and are fed with 90° phase difference resulting in a circularly polarized antenna array. For the 2.45 GHz antenna, an elliptical patch is used implementing it in the middle of the square substrate that is used for the 433 MHz monopoles. The coaxial cables are connected on the dual-branch, dual-frequency rectifiers. The combined use of both frequencies results in RF-to-dc efficiency up to 70% for input power close to 0 dBm. The dual rectifiers have a common load since they are terminated with a common power management unit circuit.

The goal of this work is to study the performance of the Wireless Power Transfer (WPT) to inside the human body, while respecting the Specific Absorption Rate (SAR) limits. Therefore, the levels of absorbed power in different body parts were verified by simulation, in order to reach conclusions about the user's safety. More specifically, two biological models that represent the thigh and the arm were considered. The simulation results led us to conclude that it is possible to transmit approximately 140 mW on the limbs location, while respecting the SAR limits. In turn, it is possible to receive a power superior to 93 µW inside the human body. Additionally, real tests were also carried out in three subjects to verify the power attenuation related to each body structure.

In this work, the authors demonstrate the potential of 5G/mm-wave signals, coupled with wide-coverage Rotman-lens-based harvesters (a.k.a. tag) to achieve efficient and long-range powering. First, the rationale for the approach is described, before the elements of the harvester and their design specifications are presented and their performance is reported. Finally, the emitting system is detailed, followed by the presentation of its use with the tag to demonstrate long-range wireless power transfer (WPT) at mm-wave frequencies. For the first time, a relatively-compact rectenna system is shown to be able to collect 5G signals at ranges exceeding 16m with a wide angular coverage, thereby extending the range relative to previous efforts by more than 5x and demonstrating a pathway towards the emergence of the Wireless Power Grid (WPG), a key to enabling the accelerated deployment of energy-autonomous wireless sensors ubiquitous constellations for digital twinning, smart cities, and intelligent infrastructure.

In this paper, a compact broadband CPW-fed circularly polarised elliptical-slot antenna with an inverted-L tuning stub is proposed. The antenna impedance is optimized for broadband operation from 1.62 GHz to 2.97 GHz. The measured CP bandwidth is 934 MHz (1.747-2.681 GHz), that covers common wireless communication bands GSM 1800, GSM 1900, 3G/LTE 2100, 3G/LTE 2300, 4G/LTE 2500, and 2.4G Wi-Fi bands. This makes the designed antenna an appropriate candidate for ambient RF energy harvesting purposes.

In this paper, we propose a novel radial line planar phased array in which helical antenna elements are individually rotated by their respective connected micromotors to realize dynamic beam-scanning. We designed, fabricated, and evaluated a 7-circle array with 168 helical antennas fabricated using molded interconnect device technology. The prototype antenna exhibits dynamic and accurate beam-forming performance, and also exhibits a low reflection coefficient of less than −17 and high antenna efficiency of 77%.

ERA5 reanalysis provides meteorological parameters that can help to predict atmospheric propagation effects. We investigate the accuracy of using ERA5 single level parameters, TCWV and TCLW, to calculate water vapor and cloud attenuation, respectively, in El Alto (4065 m.a.s.l, Bolivia) and Madrid (633 m.a.s.l, Spain), locations having different climatological conditions. The assessment is performed using as reference the attenuation predicted by physical models combined with atmospheric vertical profiles from radiosondes: 4 years (El Alto) and 8 years (Madrid). The most recent global prediction models from ITU-R are also implemented to complete testing analysis: P.676-12 and P.804-8 global maps based methods. The results obtained show that water vapour attenuation from TCWV predict statistics than can be used with small errors. Cloud attenuation from TCLW show large discrepancies in El Alto. However, in Madrid, good agreement with RAOBS-based statistics is observed when using Salonen08 Tunned model as cloud detection model.

The objectives and the preliminary results of the RadioSatMet numerical simulator are here described. The simulation chain is aimed at assessing the radio-propagation channel over the coverage region of a geostationary satellite communication (SatCom) system, featuring adaptive techniques as smart gateway diversity, through link quality estimates provided by its ground terminals as well as numerical weather prediction data. The RadioSatMet channel assessment system generates short-term statistical nowcasts and forecasts of the propagation conditions in each point of the coverage area. The RadioSatMet channel assessment output feeds an end-to-end system simulator, which evaluates the performances of the SatCom system with a particular focus on its gateway stations, in terms of data throughput, number of gateway switches and availability gains that can be achieved by using these methods.

The power spectra associated with wideband transionospheric signals received at Ascension Island (7.93oS, 14.25oW) during an observational campaign in October 2016 displayed flat and selective fading. The present contribution will combine the Method of Moment with the thin amplitude and phase screen formulation, in an attempt to identify structures that could be responsible for the observed behavior.

With increasing data rate requirements on SatCom systems there is a push to use higher frequency carriers. Although free space optical communications would meet these demands, they are severely limited by the weather conditions affecting the ground stations. Therefore, it is important to model these phenomena to predict the possibility of link outages so that an appropriate fade mitigation technique can be applied. This contribution aims to extend a model in the literature (Stochastic Model of Clouds) to include the time variability of the cloud field. The temporal evolution is studied using satellite observations and is introduced into the model by inputting ERA5 data chronologically, which has been linearly interpolated to a temporal resolution of 1 minute. The new model is then used to study the effect of site diversity for the mitigation of cloud attenuation on a GEO-Earth optical link operating at 1.55 μm.

The internal structure of small solar bodies are not well-known yet. The imaging of the interior of asteroids and comet will provide important information about their formation. In this paper, we aimed to provide a fast and efficient method to roughly image the shape and the interior of small bodies of the Solar system. We focused on monostatic measurements on two analogues of the 25143 Itokawa asteroid. The back-propagation technique was applied to promptly image the shape and internal structure of the analogues. The result shows the external shape of the analogue and that the inner void core can be reached and distinguished.

The topology optimization based on iterative changes of discretization is introduced. The optimal solution on coarse discretization is translated and enhanced on dense discretization. The similarity matrix used for solution translation is defined. Two examples of Q-factor minimization are shown to depict improvements in evaluation speed.

The problem of computing 2D EM wave scattering from rough surfaces is addressed using an integral equation formulation discretised using the method of moments. Successive Symmetric Over-Relaxation (SSOR) is applied to the governing matrix equations along with eigenvalue deflation which is designed to separately account for the effect of those eigenvectors of the iteration matrix that have eigenvalues greater than 1. Numerical results are presented applying the method to a variety of scattering profiles and examining the resultant convergence performance.

We present a boundary element method for electromagnetic scattering analysis, formulated in terms of the magnetic vector and electric scalar potentials rather than electromagnetic fields. The proposed potential-based formulation does not rely on the mutual coupling between electric and magnetic fields, and is therefore able to simulate dielectric objects over a wider range of frequency than is possible with state-of-the-art field-based methods, as demonstrated via numerical examples.

For waveguide devices, Mode-Matching represents one of the most widely used tools to compute the electromagnetic behaviour of structures due to its ability for the accurate modelling of discrete discontinuities. As devices with higher-order symmetries appear in the literature, it becomes relevant to study how it would affect the technique to use sets of modes which also have higher-order symmetry properties, such as discrete rotational symmetry. In this paper we provide a tailored Mode-Matching formulation which is capable of handling rotationally symmetric modes, while also discussing its most important properties. It has been used to analyse a variety of devices appearing in existing literature, in all of them greatly reducing the computational time and amount of modes needed for their correct modelling with regards to general-purpose Mode-Matching.

The physical optics (PO) approximation is widely used for scattering analysis involving electrically very large objects. A key step in its application is structural shadowing determination with respect to the source field. This requires determining which parts of the scatterer are visible (line-of-sight) to the source. The results presented in this paper are concerned with plane wave illumination shadowing determination for mesh-based PO. The authors have been developing a multi-level field-of-view buffer-based shadowing determination algorithm with the objective of yielding linear (optimal) runtime scaling even under very extreme circumstances. This paper reports the most recent results obtained with this algorithm, comparing it with a multi-level quadtree-based reference scheme, for a challenging example featuring both severe mesh inhomogeneity and grazing incidence. Linear runtime scaling is demonstrated. Further results will be presented at the symposium.

This paper reports the conceptualization, and analysis of a geometrical approach to determine the shift in the in-phase reflection of three conformal meta-surfaces (MS). For the proposed approach, a planar array consisting of MS unit cells (MS-UCs) of a given dimension is drawn on a circle of desired radius (r). The path traveled by the reflected and incident EM wave in terms of an electrical length results in the shift of reflection angle. For the validation purpose, the conformed arrays are simulated under x- and y-polarized EM waves. The sum of the incident and reflected phases resulting in total shift is determined theoretically and compared with the simulated shifts of the three arrays. Furthermore, one of the conformed arrays is experimentally evaluated under the TEM incidence and compared with the theoretical and simulated result. The excellent agreement between the theoretical and measured results demonstrates the effectiveness of the proposed work.

In this paper, the scattering of a Bessel beam by PEC and dielectric circular cylindrical scatterers is analyzed and discussed. In particular, it is shown that the scattering by nondiffractive beams is in general spatially localized in both cases, due to the remarkable focused beam features: the wavefront inside the main beam is locally planar, and the sidelobes are not so high, due to the abrupt amplitude shaping of the zeroth order Bessel distribution. The inherent localized scattering process paves the way to novel applications in microwave imaging and ground penetrating radar design.

In this paper, a substrate integrated waveguide (SIW) loaded with three pairs of modified complementary split-ring resonators (CSRRs) is presented, in which the subwavelength waveguide passband can be significantly increased due to the appearance of new electromagnetic couplings between the different resonators. The obtained results are compared to those provided by a more classical topology based on CSRRs periodically etched along the waveguide wall, showing a significant bandwidth improvement, while maintaining a good matching level.

A novel design of a dual band metasurface unit element using two diodes for independent phase shifting in two frequency bands with low reflection losses is presented. Control of the capacitance and thus of the reflected phase can be achieved by independently applying a reverse bias to the two air-bridged Schottky diodes that are embedded on the phase-shifting element. Simulations of the proposed design are presented and the currents and losses are studied. CST Microwave Studio was used to evaluate the tuning range and reflection characteristics of the proposed design.

This paper presents a 2-bit unit cell for reconfigurable intelligent surface (RIS) applications of beamforming and beam-steering in the frequency range 2 (FR2) from the fifth generation of mobile communications (5G). The proposed unit cell is based on a printed split-ring resonator (SRR) loaded with a varactor diode. The SRR-based structure comprises two circular loops connected by a varactor diode at the top and a ground plane at the bottom, resulting in a 0.245x0.245λ0 total area. The complete unit cell element encompasses four conducting layers, in which the first two ones form the SRR. RF chokes are printed at the middle layer to isolate the DC circuit, and the bias lines are routed at the fourth layer. The unit cell has been conceived using the full-wave electromagnetic solver ANSYS HFSS. Its numerical results demonstrate a reflection phase shift up to 270º and reflection magnitude higher than 0.5 at 24.5 GHz.

This paper presents a detailed investigation of the propagation of noise generated by a switch mode power supply (SMPS) across an automotive sensor Printed Circuit Board (PCB). The noise propagation is simulated using a full 3D model of the board. CST Studio Suite was used to import the PCB and component models, perform the simulations and visualize the surface current distribution and the corresponding noise distribution. The paper demonstrates how the ground vias arrangement is critical for full understanding of propagation of the noise and its mitigation.

We propose an alternative metasurface-based approach for the synthesis of Bessel beam launchers at microwaves/millimeter waves, based on an inward cylindrical traveling wave aperture distribution. Our approach simply allows the outward-to-inward cylindrical feeding wave conversion by metallic dihedrons. Although more involved from the manufacturing viewpoint with respect to single layer devices, it can in principle avoid the computationally-heavy design of holographybased Bessel beam launchers. The preliminary numerical results show the effectiveness of the proposed technique.

Additive manufacturing offers new possibilities in the design of innovative antennas. In order to fully exploit its potential, it is necessary to fully use the capabilities offered by the 3D printing technology. 3D-printed structured dielectrics are currently receiving a lot of interest in this respect. However, the characterization of the dielectric properties of such crystal structures is not easy and often assumptions on such properties need to be done. This paper shows a characterization of additively manufactured structured dielectrics in terms of their permittivity and loss tangent in a simple cubic (SC) and face centered cubic (FCC) crystal geometry with different fill fractions. Measurement results are compared to values predicted by the Maxwell-Garnett effective media approximation and by the effective refractive index extracted from a three-dimensional plane wave expansion method (PWEM) in the long wavelength limit.

A single-layer frequency selective surface (FSS) polarizer is proposed as a linear-to-circular polarization converter, operating at 5.2 GHz for 5G applications. The analyses are based on the magnitude and phase of the transmission coefficient of two orthogonal electric field components. The four-arms star geometry used in the FSS polarizer is simple to design, and equations are provided. The design approach is validated by a good agreement between numerical and measured results.

The problem of electromagnetic plane wave scattering by doubly periodic dielectric structures composed of spherical radially inhomogeneous absorbing elements of black hole type arranged on a perfectly conducting screen is considered. An algorithm accounting for the features of the black holes is developed on the basis of the hybrid projection method for solution of the problem. A number of numerical results characterizing both the effectiveness of the algorithms themselves and the properties of the black-hole-based absorbing structures are presented and discussed.

In this paper, a low radar cross section (RCS) dipole antenna is proposed by using an absorptive frequency selective reflection (AFSR) structure as the ground plane. The proposed AFSR consists of a bandstop resonator integrated with a broadband absorber and exhibits a reflection notch within the absorption band. The reflection notch achieved in the AFSR structure coincides with the operating band of the dipole antenna. The performance parameter of the dipole antenna co-designed with the AFSR structure is nearly the same as obtained with a metallic reflector backed dipole. However, a significant out-of-band RCS reduction of more than 20 dB in the two side-bands on both sides of the operating band is achieved for the antenna co-designed with the AFSR structure compared to the antenna backed with metallic reflector. Furthermore, the AFSR backed dipole shows an increase in antenna gain by more than 1 dB compared to the reflector backed dipole.

This paper presents a 3-D printing-compatible wideband absorber with high angular robustness. A periodic structure, composed of Hanoi-Tower shaped resonators, is fabricated with a lossy 3-D printable dielectric material using additive manufacturing, and glued on a magnetic elastomeric material. Exploiting the resonating modes in the periodic resonators, high absorption is achieved over a large bandwidth. The resonators' shape and dimensions are chosen accordingly to the material properties so that a high angular robustness is reached. Moreover, the presence of a magnetic support enhances the absorption capabilities of the structure, specially for the TM polarization, where a reflectivity below -10 dB for most incident angles over the 4-12 GHz band is reached. Finally, diffraction phenomena happening at high frequencies are studied, showcasing that high-order diffraction can be avoided by reducing the size of the structure and increasing the permittivity of the dielectric material.

In this study, we propose a multi-functional unit-cell that integrates reflectarray and linear polarizer functions together. The unit-cell is composed of a multi-layer structure and depending on the polarization, it can perform as a reflectarray or transmission type linear polarization converter. Our results demonstrate that in the reflection mode, the unit-cell shows high reflection magnitude around one and a nearly full phase coverage of 310° at 14GHZ. In the transmission mode, the unit-cell functions as a highly efficient linear polarization converter with PCR more than 95% in the broad frequency range of 3 GHz to 14 GHz. Our results reveal that the proposed unit-cell is suitable for multi-functional applications such as bidirectional wireless Communication.

A MLFMM-FFT based strategy for the computation of electromagnetic (EM) radiation and scattering in dielectrics is presented. The objective is to reduce the computational resources required for the application of the method of moments (MoM) to problems with electrically large dielectric structures. For this purpose, the storage of the near-field couplings in the MLFMM algorithm is reduced taking advantage of the Toeplitz symmetries present in regular hexahedral meshes. Therefore, the rigorous MoM matrix becomes smaller, thus significantly reducing the amount of memory required for the computation in this kind of problems. The FFT is employed for a fast computation in the convolutions required in the near-field part of the algorithm. In addition, a new approach for the numerical treatment of the transitions between dielectrics and dielectric and the free space is introduced. The proposed strategy is validated with the computation of the radar cross section (RCS) of a classical dielectric sphere, compared with the classical MLFMM approach. A practical example of an antenna covered by an epoxy radome is also computed, whose results verify the efficient memory and computation times achieved.

A volumetric method of moments (V-MoM) for the analysis of integrated antennas is presented here. The developed numerical procedure discretizes the domain with a uniform and hexahedral mesh. For antennas radiating in the presence of dielectric slabs or lenses, the discretization required for the dielectric materials is typically coarser than the one required for the antenna. To enable a uniform mesh, a technique is proposed that allows efficient simulations of the dielectric together with the antenna feed. The antenna is first analyzed in a homogenous infinite medium. Subsequently, an auxiliary antenna is defined that is equivalent in terms of impedance, but characterized by much coarser details. The auxiliary antenna is then analyzed together with the finite size dielectrics, with a computationally efficient simulation.

The paper reports a second-order approximation of the transition boundary condition for not very thin layers of non-dense materials. It allows reconstructing with an error of less than 1% the scattering from a dielectric slab characterized by a thickness of the order of a tenth of wavelength, even when the relative dielectric constant is 2. Furthermore, the independence of the formulation from the incidence angle of the impinging wave allows its implementation in a numerical method as the method of moments.

Fundamental bounds play an important role in antenna design. Using method of moments and electric field integral equation, this paper shows a formulation of fundamental bounds based on quadratically constrained quadratic programs. This methodology is applied to two representative and challenging examples. The first example examines Yagi-Uda antenna and compares it with performance limits on Q-factor, radiation efficiency, and directivity. The second example shows how to determine fundamental bounds when a designer has far-field constraints. In their entirety, the examples demonstrate variability and generality of this treatment and also recall the existence of an open-source computational package, which can be used for evaluation of fundamental bounds on various metrics including their mutual trade-offs.

This article presents a simple matching technique to control surface-waves (SWs) by using a finite metasurface matching section. The approach is based on a sub-wavelength array of patches which are employed as a simple and effective approach to control and guide SWs on a grounded dielectric slab (GDS). In order to excite the fundamental TM0 SW mode, a horn-shape surface-wave launcher (SWL) in substrate integrated waveguide (SIW) technology is employed. The structure and the matching metasurface are modeled with an equivalent circuit.

This paper presents a novel technique to implement crossed dipole antenna fed by Substrate Integrated Coaxial Line (SICL) technology. The inherent advantage of out of phase surface current of the SICL transmission line is utilized efficiently to excite the two dipole antennas. The crossed dipole is implemented to obtain dual band response at 26 GHz and 28 GHz. Two 45 inclined dipoles are printed on the top/bottom of the substrate and simultaneously fed by top/bottom plate of the SICL line. SICL 1:4 power divider is employed to feed four crossed dipole antenna to form an array. The array exhibits a gain of 9.7 dBi and 10 dBi at 26 GHz and 28 GHz respectively exhibiting wide 3.1 GHz bandwidth . The cross polarization better than 20 dB is obtained for the proposed design. The proposed antenna finds its suitability for the much focused 5G millimeter wave frequency bands.

The design and numerical simulations of a microwave sensor for the moisture content of traditional Carasau bread is presented in this paper. The results highlight the ability of a simple patch antenna to discriminate small percentage variations in water content in the food product, avoiding misinterpretations due to other parameters modifications, such as distance of the sensor and thickness of the bread sample.

The Industry 4.0 paradigm calls for engineering solutions for monitoring the industrial production and quality of food products. Microwave devices can be powerful tools in this scenario. This work deals with the preliminary design of a double ridge waveguide to perform indirect measurements of the complex permittivity of a traditional food product from Sardinia (Italy), i.e. the Carasau bread, produced in a small bakery industry. To this aim, the complex dielectric permittivity of doughs was measured with open-ended coaxial probe in the range 0.5-8.5 GHz. The dielectric spectra were fitted to a third-order Cole-Cole model. Then the data were used to numerically study the microwave signal propagation in the double ridge waveguide investigating different sample configurations. With our full-wave simulations, the thickness of the sample holder, the occupation length of the sample in the waveguide, as well as the inclination angle were determined to achieve suitable transmission performance.

In this paper, a Chipless RFID tag design based on Radar Cross Section (RCS) operating principle is proposed. The tag is implemented using a series of circular ring resonators to enable tag identification. The resonators are simulated and then fabricated on an FR4 substrate. A calibration technique using a ring resonator to improve the detection of 8-bit data is proposed and demonstrated. The fabricated tag is measured at a distance of 160 mm using the monostatic RCS method. The measurement results verify the simulation results and show accurate detection of the encoded information.

The technological advances in electronic devices and the Internet of Things bring us to be surrounded by multiple sensors in the coming years. These devices should be conformable and adapted to small or irregular shapes and surfaces. This is why flexible materials are becoming important in this field thanks to their lightness, stretchability, and robustness especially in wearable electronics to get integrated on clothes for biomonitoring. Our proposal in this paper concerns the design, printing process, and performance of a novel antenna on a polyimide flexible substrate. It is based on a loop antenna and has dimensions of 40 mm × 35 mm × 0.127 mm. Its very wideband behavior from 2.4 GHz to 4 GHz allows targeting S-Band applications such as LTE and Wi-Fi. Interesting performances are also achieved in terms of radiation patterns. At 2.45 GHz, the maximum antenna gain is about +2.6 dBi with an omnidirectional pattern but at higher frequencies, the antenna is more directive with a higher gain.

A compact and broadband coplanar waveguide (CPW) fed ring pair slot antenna is presented in this paper. The designed antenna operates in the frequency range from 2.6 to 7.13 GHz (93%) for |S11| ≤ -10 dB with a peak gain of 5.06 dBi at 5.6 GHz. The designed antenna is uniplanar having the size of 0.39λ0 × 0.3 λ0 ×0.007 λ0 (λ0 is the wavelength at the lowest operating frequency in free space). The proposed configuration has a stable radiation pattern over the operating frequency band. The designed antenna is fabricated and simulated results are validated with measured results.

The procedure of estimating the angular dependent delay of an Ultra Wideband (UWB) antenna, directly in frequency domain, is presented. It is shown that in this approach any occurrences that can lead to inaccurate results, such as the windowing effect, can be entirely avoided. It alleviates the need to design a specific pulse, since the transfer function can be obtained by a frequency sweep. Moreover, polarization mismatch is accounted in the analysis. To this end, an UWB monopole antenna is designed and it is simulated with time and frequency domain solvers. The simulation results demonstrate that only frequency domain analysis is sufficient for the delay estimation. The outcome of this work provides a clear procedure for obtaining the angular dependent delay of an antenna in an accurate way.

This paper presents an Ultra-Wideband (UWB) patch antenna which is aimed to be an Anchor-antenna in UWB localization systems. It can operate distinctively in two different UWB frequency channels. Both of these channels have 500 MHz bandwidth, the lowband channel is centered at 4 GHz and the highband channel at 6.49 GHz. Reconfigurability to switch from one channel to another is achieved by changing the size of the radiating element. Additionally, this UWB antenna is aimed to be circularly polarized over both channels, which is realized through two branchline couplers placed on a bottom layer. Results of reconfigurability and circular polarization operation are verified by simulation and measurements.

A compact low-loss reconfigurable phase shifter based on gap waveguide (GW) is proposed. The phase shifter is realized by controlling the different lengths of the transmission line. A movable metal block is placed on the transmission line, and different phase shifts can be obtained through different moving distances to realize reconfiguration. In this paper, the possible errors in practical application are considered and the solutions are given. The use of GW technology enables the design to achieve low-cost manufacturing and simple implementation. The simulation S-parameters show that the impedance matching bandwidth with reflection coefficients below −15 dB is 19.1%, covering 71 − 86 GHz, and the maximum phase shift of 180° can be achieved.

A feasibility study to design a complex X/Ka-band feed system that also incorporates a Ka-band Radar function is undertaken. An unconventional wide-band Ka-band polarizer design was needed due to the high-power nature of the application.

Reflector antennas systems use struts in order to antenna structural parts such as feeders or sub-reflectors. Struts' presence generates scattered fields that affect the antenna performance. In this paper, a comparative study between different struts' materials and cross-sections is presented. For the analysis, a Cassegrain configuration was used, designed for X-band operation. Struts' analysis was conducted through simulations at 8.425 GHz. Two different struts' positions (setups) were also studied. Detailed discussion on performance results is presented.

To reduce the coverage holes from the base station, reflectarray has gained attention for 5G mobile wireless communication. This paper proposes the design method for dual frequency and dual polarization reflectarray operating at 28 and 39 GHz. The proposed method combines the modified phase and pattern mask, which can reduce the sidelobe level of the dual frequency and dual polarization reflectarray. This paper demonstrates the reflectarray designed by the proposed method in simulation and measurement.

Broadband Pancharatnam-Berry (P-B) phase and dynamic phase hybrid unit cells for realizing dual circularly polarized (DCP) independent beam control reflectarrays is proposed. The unit cells present independent reflection phase shift for left hand circularly polarized (LHCP) and right hand circularly polarized (RHCP) incident waves, which are achieved by simultaneously utilizing P-B phase and dimension vary dynamic phase. A broadband P-B phase unit cell with reflection coefficient greater than -0.5 dB in the range of of 6.9-15.7 GHz (bandwidth of 77%) is designed, and then independent dynamic phase achieved by adjusting the dimension of the unit cell. Simulation results reveal the P-B phase shift range and dynamic linear phase shift range of the single-layer unit cells are 360◦ in the range of 8-12 GHz (bandwidth of 40%).

Estimation the reflected field phase, admittance and unknown basis functions coefficients are presented for the case of single-layer rectangular slot element in unit cell. The analysis is based on a solution of an integral-equation system with the Method of Moments in spectral domain. Only one basis function is used for the analysis. It is shown that this approach provides satisfactory accuracy for the development of the slot reflectarray antennas. Characteristics of the unit cell and reflectarray antennas obtained by proposed approach and full-wave simulations are presented.

An integrated lens antenna (ILA) is desired to have high directivity and a wide steering range. The directivity of an ILA is proportional to its diameter. In this work, the relation between the diameter and the scan loss of the elliptical and hemispherical ILAs is studied using the ray-tracing simulation. The simulation study finds that the scan loss of an ILA, both elliptical and hemispherical, is proportional to the diameter. In addition, the optimum extension lengths of the extended hemispherical ILA are presented for various diameters and relative permittivities which serve as the design guideline for ILA designers.

A gradient index flat lens with a directive beam-steering radiation pattern and configurable dual circular polarization is discussed in this contribution. The dielectric lens, designed to operate at W band, is perforated to achieve a radial decreasing dielectric permittivity characteristic, so high-directivity beam with planar wave front can be obtained. A precisely designed stereolithography 3D structure is adhered to the surface of the lens to turn the vertical or horizontal electric field polarization into RHCP (Right-hand circular polarization) or LHCP (Left-hand circular polarization), respectively. An open-ended square waveguide is used as feeding structure to generate the vertical and horizontal polarization exciting the two degenerate modes TE10 and TE01. The system can achieve a wide beam-steering range of ±30° in both azimuth and elevation planes, attained by applying precise displacements to the feeding square waveguide position. In order to experimentally validate the antenna performance, the design is manufactured and measured

In this study, a simple decoupling method using parasitic elements (PEs) connected by a bridge line (BL) for multiple planar inverted-F antennas (PIFAs) is proposed. The PEs and BL only need to be loaded in close proximity onto the PIFAs. Thus, redesigning the original antenna elements is not necessary. This feature is useful when design conditions make it difficult to redesign the original antenna, for example, to redesign small modular antennas. For the case of two PIFAs, using PEs and BL reduces the mutual coupling from −6.6 to −16.7 dB, and simultaneously maintains the resonance at the desired frequency (2.0 GHz), resulting in an improved total antenna efficiency from 77.4% to 96.0%. In the case of four PIFAs, the proposed method still showed its efficiency in decoupling, but some deteriorated efficiencies are also observed compared with the case of two PIFAs. This deterioration will improve in the future.

In this paper we present a technique to broaden the beamwidth of conventional patch microstrip antennas by using parasitic elements. This technique allows to keep the main advantages of microstrip antennas while increasing their beamwidth. We provide guidelines on how to tune the shape of the pattern from directive patterns to broad beam by tuning a few key parameters. Using this technique, the beamwidth of a regular patch antenna can be increased from the usual 70º up to 200º, and is compatible with linear and circular polarization. The antenna presented as an example in the paper covers the ISM band at 2.4GHz.

In this article, three dual circularly-polarized K-band horn antennas are designed and experimentally validated. All designs are based on a common topology: a square waveguide input, a bowtie-shaped polarizer, and a flare section. Either left or right-handed radiation can be achieved by exciting either mode in the square waveguide. The bowtie polarizer outstands as a simple, easy-to-manufacture way of obtaining circular polarization. The three designs differ just in the flare section: a circular aperture, a square aperture and a bowtie-shaped aperture have been considered. The advantages of each aperture type will be discussed. The prototypes have been manufactured by Direct Metal Laser Sintering, allowing a single-block assembly. Over 20% bandwidth with axial ratio under 3 dB and gain around 19 dBi has been experimentally obtained.

This document follows a previous article \cite{eucap2021} which present the design of a Dielectric Resonator Antenna (DRA) developed by ANYWAVES with the support of the French Space Agency (CNES) and the help of an academic partner XLIM. This antenna is circularly-polarized, dual-band (Upper-L-Band (1.559 - 1.61 GHz) and TT&C S-Band (2.025 - 2.29 GHz)) and designed to be integrated on a CubeSat or Nanosatellite. The particularity of this DRA is that the dielectric part is a structured 3D-printed block of Zirconia with two different permittivities. Two different feeding lines have been designed: with and without an integrated diplexer. Two breadboards of this antenna had been fabricated and measured in the premises of XLIM.

Parallel electromagnetic solvers require efficient strategies to distribute the mesh of large structures encountered in advanced antenna designs. In addition, parallel solvers based on the adaptive integral method (AIM) require processes to access additional mesh entities that lie within the near region of their mesh partition. In this paper, we propose a parallel solution for loading, processing, partitioning, and redistributing the mesh of AIM-based solvers. The proposed method is demonstrated on problems as large as 200 wavelengths, with up to 200 million unknowns, and up to 8000 cores involved.

This article presents a study of the tunable impedance matching to our recently reported compact self-matched triple-band brain-implantable planar-inverted-F antenna (PIFA). It operates at Medical Device Radiocommunication Service (MedRadio) band (401-406 MHz) and Industrial, Scientific, and Medical (ISM) bands (902-928 MHz and 2400-2483.5 MHz). To achieve this, we investigated the optimal reflection coefficient characteristics of PIFA at desired frequencies by employing four π- and T-type matching circuits. Our results show that a T-type circuit selected for further assessment provides suitable fine-tuning possibilities for all combinations of desired upwards and downwards frequency-tuning of the three operating frequencies to ensure reliable wireless implant communications.

With the exponential advancements realized in communication technologies, synthetic biology, and nanotechnology, now it is time to aim high and design new generation implants. To achieve this vision, this paper presents a novel sensing platform based on genetically engineered bacteria and a repeater antenna system, including a biodegradable in-body reflector antenna and on-body reader antenna. The biodegradation process is controlled by the engineered bacteria which in the future will be utilized to sense a molecule of interest. The biodegradation, hence, the sensing can be wirelessly tracked. In this paper, we present the control of biodegradation experimentally by the engineered bacteria and show the wireless tracking numerically. The sensing at 1 cm implant depth in fat tissue in the 2.4 GHz ISM band is demonstrated.

Two different bidirectional periodic leaky-wave antennas (LWAs) are presented for the millimeter-wave (mm-wave) band with suppressed stopbands and orthogonal radiation directions: a bidirectional side-fire antenna with left/right in-plane radiation and a bidirectional slot-pair antenna with top/bottom out-of-plane radiation. The operations of these antennas are confirmed using full-wave simulations, with a broadside frequency of approximately 28 GHz. These antennas can be individually engineered to form various radiation patterns in each of their radiation planes, and can further be combined to design a tetra-directional periodic LWA.

Compared to conventional uniformly spaced arrays, sparse arrays are effective and economical for many application scenarios. For example, sparse arrays can lower the peak sidelobe level (PSLL) or narrow the main lobe half-power 3dB beamwidth (3dB BW) of the array pattern with fewer elements. This can help to save on the number of antennas, and the supporting hardware costs, as well as improve the angular resolution which is useful for automotive radar systems and target identification applications. Furthermore, when fewer elements are employed, as in sparse arrays, the spacing between the elements can become larger, which can lead to a reduction in the mutual coupling. This paper will focus on implementing a hybrid approach to numerically determine an optimal 4x4 multiple-input multiple-output (MIMO) array considering simulated annealing and particle swarm optimization (SA-PSO). Results will show that the technique can achieve lower PSLL or narrower 3dB BW with 8 fewer elements when compared to a corresponding 16 element uniform linear array (ULA). To the best knowledge of the authors, this is the first time that such comparisons and design techniques have been applied to sparse MIMO arrays whilst considering a hybrid SA-PSO synthesis algorithm.

With the application requirements of wireless technology in implantable bioelectronics, knowledge of the fundamental limits for implanted antennas becomes critical. In this work, we investigated the variation of maximum power density within simplified body phantoms, caused by changes in the operating frequency, implantation depth, body phantom radius, and source size. Both spherical and planar body models are studied, and the corresponding results are compared to an efficient approximation method. The summarized results are used to derive design rules and can be used as benchmarks for the design of most implanted antennas, especially for shallow implants.

A transparent spherical spiral antenna for endoscopy capsule systems for gastrointestinal monitoring is presented in this article. The capsule antenna is designed for operating in the Medical Implant Communication Systems frequency band (i.e., 401-406 MHz) and has an impedance bandwidth of 397-409 MHz. The transparency of the antenna allows it to be implemented in front of the camera. This leads to more available space inside the capsule for embedding more subsystems. The proposed antenna also has a circularly polarized omnidirectional radiation pattern. These characteristics allow a stable wireless communication link during the monitoring operation.

A circularly polarized implantable antenna working at 915 MHz industrial, scientific, and medical (ISM) band is presented. A meander line is used for miniaturization purposes, while a U-shaped structure is used not only to guarantee circular polarization performance but also to shift the band to lower frequencies. The designed antenna shows an impedance bandwidth of 20 % from 809.4 to 989.8 MHz and an axial ratio (AR) bandwidth of 27 % from 770 to 1010 MHz. The proposed antenna has a compact size of 5.2 mm × 5.6 mm. The proposed antenna achieves an acceptable gain value of -23 dBi. Furthermore, the geometry of the proposed antenna remains simple with a full ground plane and without using any via holes. Finally, the fabricated prototype has been experimentally tested inside minced pork, salmon fish, and beef meat, and the measured results show good agreement with the simulated one.

This work focuses on the investigation of the degree of possible detuning that may be observed in the impedance response of ingestible antennas during the transition through the gastrointestinal tract. For this investigation, two antennas are used: a meandered dipole and loop antenna. The antennas conform to the inner surface of the biocompatible capsule shell. They are optimized in spherical homogeneous time-averaged gastrointestinal phantoms at 3 frequencies of interest: 434 MHz, 1.4 GHz, and 2.4 GHz. Next, the optimized antennas are simulated in 3 different phantoms, each mimicking electromagnetic properties of one of the tissues in the gastrointestinal tract. The impedance response of each design in 4 different tissues is discussed. The results show that the maximum shift in the operating frequency is 7 MHz, indicating that the presence of the encapsulation layer makes the considered antennas robust against the changes in the electromagnetic properties encountered through the gastrointestinal tract.

This paper presents a possible solution to enhance electromagnetic transmission to an implantable/wearable device in wireless power transfer systems. Based on an analytical approach we have developed, we show how it is possible, using wearable dielectric cylindrical scatterers, to increase the intensity of the transmitted field to a possible receiver, which may be arranged in the textile fabric of a garment or implanted in the underlying biological tissue. In particular, we show some parametric studies on the dielectric constant of scatterers, which can be easily integrated into a fabric, showing which configuration achieves the greatest increase in electromagnetic transmission. The electrical parameters of the biological and textile tissues are considered in the millimeter frequency range (f = 24 GHz).

In this paper, a novel textile star-shaped supershaped patch antenna is proposed for 5G applications, operating at 3.5 GHz. The Gielis Formula, also called Superformula, was used to design the antenna and thus minimize its patch size. The characteristics of the antenna, such as return loss, realized gain and radiation pattern are simulated, and the return loss is compared with the measured results. The designed antenna attains a -45.48 dB return loss at 3.5 GHz, with operational bandwidth from 3.43 GHz to 3.56 GHz for -10 dB, with the peak gain around 8.5 dBi for 3.5 GHz.

A low-cost single-layer substrate-integrated waveguide (SIW) cavity-backed slot antenna is proposed for millimeter-wave applications. The structure is designed to operate at the W-band. The T-shaped slot antenna is placed on the back-side of the SIW and fed by a grounded coplanar waveguide (GCPW) transmission line. A transition between the (GCPW) and the SIW is also designed. The simulated results provide that the antenna has a stable gain over the frequency range (98.79-100.56) GHz with a maximum value of around 6 dBi also high radiation efficiency.

In this paper, a compact wideband antenna-inpackage (AiP) for 5G mmWave applications in the 39 GHz frequency band is presented. The proposed 1x2 antenna array consists of two identical patch antenna elements, which are designed, simulated and fabricated using a multilayer PCB substrate technology suitable for chip embedding. To improve the antenna bandwidth two U-shaped slots are etched in each patch element. The fabricated 1x2 U-slot patch antenna array exhibits a measured impedance bandwidth of 3 GHz at 39 GHz frequency band, and a measured peak gain of 8.8 dBi.

This paper presents an innovative and advanced miniaturized 5G module of wideband dual-polarized (pol.) millimeter-Wave (mm-Wave) antennas-in-package as non-mm-Wave antennas (AiPaA) for handsets. That is, the module of mm-Wave antennas-in-package (AiP) can also function as virtual equivalent non-mm-Wave antennas. This AiPaA module can cover 3GPP mm-Wave bands n257, n261, n260 and the mm-Wave band (24.75-27.50 GHz) in China. Moreover, without physical non-mm-Wave antennas, the module itself can operate in 3GPP non-mm-Wave bands n78 and n79. Thus, this AiPaA module can serve as a miniaturized compelling 5G antenna total solution to handsets without expanded volumes for physical non-mm-Wave antennas.

An innovative and practical integration of 5G millimeter-Wave (mm-Wave) antennas and 5G non-mm-Wave antennas based on the flexible printed circuit (FPC) for mobile phones is proposed. Therefore, the integrated antennas are well conformal to the curved phones shapes due to the flexible substrate. The integrated 5G mm-Wave antennas are in a 1 × 4 array which covers the 3GPP band n261 (27.5-28.35 GHz) and the two 5G non-mm-Wave antennas are integrated in an equivalent form by reusing the ground of the mentioned 5G mm-Wave antenna array to achieve MIMO function in the 3GPP band n79 (4.4-5.0 GHz). The FPC-based integrated 5G antennas (with a total length of 26.07 mm) can be attached on the inside of the curved edges of back covers to attain the elegant applications to mobile phones.

In this paper, we present an innovative sensor for non-invasive detection of millimeter inclusions by using a microwave radiating system. The proposed device consists in a microstrip self-resonant spiral coil inductively coupled to an external concentric planar probe loop, working at a frequency of 570 MHz. The microwave sensor configuration is the result of an optimization process of the spiral coil Q-factor maximization, required to obtain a millimeter resolution for the inclusions detection. In particular, the detection is achieved by observing the amplitude and frequency shift variation of the external planar probe input impedance. We performed full-wave simulations to design and evaluate the radiating system performance. Numerical results validated the introduced theorical approach, encouraging further analysis for the potential use of such sensor in biomedical applications. Indeed, the radiating device can be extremely useful in all the tasks where it is required to spot the presence of undesired and dangerous impurities in a contactless way. For instance, the sensor might be employed to detect and monitor in real-time the presence of air inclusions and blood cloths during a hemodialysis treatment, making the procedure safer for patients.

One of the most common symptoms of respiratory pandemics, like COVID-19, is cough. Its monitoring is useful to trace the progress of the disease and to evaluate its severity. Traditional measurement methods are bulky and wired. Instead, wearable and wireless technologies such as the Radio Frequency Identification (RFID) could allow the implementation of platforms able to monitor patients remotely. The monitoring of the respiratory function has already profited from the operation of temperature sensors put close to the airways as well as from the sensorization of facemasks, widely used in case of respiratory viruses. In this paper, a UHF RFID temperature sensor tag integrating auto-tuning capability is integrated inside a FFP2 facemask to retrieve temperature profiles used to count and detect three different types of coughing. All the cough shots are consistently detected by the system, and their periodicity and duration can be determined.

This paper addresses the complete process of design, optimization, manufacturing and testing of a vector array of eight longitudinal slots, devised to work on the W band with a uniform amplitude taper distribution. Comparison between simulations and measurements are shown, revealing an almost perfect match in both radiation pattern and return losses.

In this paper, we present an all-metal antenna element with multiple feeding points for wide-scan angle arrays. The antenna element is composed of two slots feeding two stacked patches backed by integrated cavities. Dielectric material is used only in the feeding part of the antenna as a substrate supporting four asymmetric striplines feeding the slots. The radiating part of the antenna is built entirely from metal and air ensuring stable thermal behaviour of the antenna for high input power levels. The array supports wide-angle scanning up to a maximum of θ=60o for all φ-planes over almost ~16% bandwidth. The antenna element may find its application in the areas involving high radiated powers, e.g. communication systems, radar systems.

An ISM band sectorial compact antenna working at 868 MHz is presented in this paper. The antenna is designed to have very low perturbations in terms of radiation pattern, bandwidth and input impedance when mounted on different environments at the rear (i.e. wood, plastic or metal support). Furthermore, the PIFA topology of the antenna allows an easy matching either to a 50 Ohm input impedance for IoT/LoRA applications or to a complex impedance value for RFID applications with the help of a simple matching circuit.

This work presents an additively manufactured helical antenna for X-Band. A comparison between stereolithography and selective laser sintering processes is made. The proposed antenna concept includes a transition from the helix coil to an X-band waveguide, which allows for matching of the antenna to the waveguide. In our measurements, the proposed antennae featured a -10dB-bandwidth of 2.8 GHz and a -20 dB-bandwidth of 0.28GHz respectively. The suggested manufacturing and de- sign process is, therefore, a major step towards enabling complex antenna geometries.

In this work, additively manufactured pyramidal horn antennas are presented which are fabricated from UV-curable polymer resin by a DLP 3D printing system and subsequently coated by copper electroplating. In order to improve printing and metal plating quality, the models are adapted following the slotted waveguide approach and build orientation is discussed to cope with support of overhanging structures. The manufactured specimens reveal almost identical performance compared to a commercially available equivalent. This way, successful application of the slotted waveguide approach is demonstrated with horn antennas for mm-Wave frequency range.

This paper proposes a dual-linear polarized compact feeding system that generates surface waves with low transmission loss. The proposed feeding system is designed for compact size and dual-linear polarized characteristics by using pillbox structure, and the hologram pattern for generating surface waves. The feeding system obtained the transmission loss of -0.74 dB(lossless material), -3.41 dB(lossy material), and reflection loss below -10 dB from 21 to 27 GHz.

This paper discusses a novel PCB transition to feed an H-plane sectoral horn array intended for use with highly integrated mm-wave beamforming devices. To maintain the half-wavelength element spacing necessary for grating-lobe free operation, the signal launch into rectangular waveguide is oriented such that the waveguide 'b' dimension aligns with the PCB edge. The fabricated design achieves a good impedance match over a 14 GHz bandwidth centred at 64 GHz.

This work proposes a 4x4 double slot antenna array based on ridged gap waveguide feeding network for 39GHz. The antenna system is comprised of three independent layers. The top layer is the radiating layer with a 4x4 pair of slots configuration, the middle one is the resonant cavity, and the bottom layer involves the ridge gap waveguide. The use of pair of slots on the radiating layer achieves an alternative solution to radiating energy, as compared to previously published work, reducing the return losses and mutual coupling between the resonant elements, in the desired frequency operation. The presented design provides high gain and directivity over 18dB, due to the planar and multilayer structure, while the reflection coefficient is below -10dB over the operating frequency range 37.4GHz-40.2 GHz, covering a 7.2% bandwidth.

A dual circularly polarized (CP) slot array antenna is proposed for V-band applications. A sliding mechanism based on the groove gap waveguide is employed to achieve the left-hand circular polarization (LHCP) and the right hand circular polarization (RHCP). Due to the use of gap waveguide technology, there is no electrical contact between the different parts of the switch and the leakage of the electromagnetic wave is suppressed. The simulation results show that the proposed antenna has axial ratio (AR) below 3 dB, and pick gain of 14 dB in the desired impedance matching bandwidth from 58-62 GHz.

he aim of this paper is to investigate the steering mechanism of the beam pattern of a helical antenna using a half-cup plasma reflector. To this end, variations of the radiation characteristics and also the direction of the main beam of the antenna due to changes in the dimensions of the half-cup plasma reflector, including its diameter and height, are numerically computed and analyzed. The simulation results show that using this structure, the beam direction can be altered in 3-D space within a solid angle of ±10 o . Also, it is highlighted that the half-cup plasma reflector may adversely affect the polarization of the helical antenna. Therefore, a trade-off between polarization and performance of an antenna based on a parametric study has to be made. Thus, in this investigation, the axial ratio of the antenna is also analyzed for each dimension. For demonstration, the study is used for the design of a circularly polarized helical antenna with a half-cup plasma reflector. Good agreement between the numerically calculated and measured results validates the presented study.

A high isolation and high gain antenna designed with polarization-dependent partially reflective surface (PRS) and polarization conversion surface (PCS) is described in this paper. It is observed that no matter what polarized source is employed, the final polarizations of the proposed antenna are identical. For demonstration, a dual-polarized square patch antenna operating at 9.0 GHz is simply employed as a TE- or TM-polarization source. The simulated results demonstrate the peak gains for two polarizations are all up to 14.4dBi, and the isolation between the two ports are more than 15 dB at 9.0 GHz. The experimental measurement results match well with the simulated ones verifying the effectiveness of the proposed antenna.

Next-generation weather radars are expected to be implemented with electronically-scanning planar phased arrays. Their scan agility could enable higher update rates and improved forecasts. However, application requirements on the polarization purity are hard to satisfy with a planar structure. Previous works in the literature have indicated a requirement of -22 [dB] on the Cross-Polarization Level (CPL) on scan under Ludwig's 2nd definition. This work presents a novel radiating element that approximates a magneto-electric dipole and has a printable planar structure. Preliminary numerical results show that the radiating element satisfies the CPL requirement in more than 98% of the scan directions of interest.

This paper introduces the DS-DMAS (double-stage delay multiply and sum) algorithm for 3-dimensional microwave breast cancer detection. In contrast to conventional confocal microwave imaging approaches, the DS-DMAS method performs the focusing twice which overcomes the limitations of conventional digital beamformers in terms of low image resolution and low contrast. This work presents image reconstruction examples based on numerical simulations with a comparison to DAS (delay and sum) and DMAS (delay multiply and sum) beamformers. Image analysis metrics have been implemented and discussed to quantitatively analyze the image quality. A significant improvement of DS-DMAS compared to both other techniques can be found.

In this paper, we investigate the gain switching performance of the software-defined radio USRP X310 with the TwinRX daughterboard and propose a method to optimize it for fast transitions. This receiver uses a complex structure of two switchable amplifiers and two digital step attenuators to realize the wide gain setting range of up to 92 dB. Our measurements of the settling time show that the bulk of transitions between two gain settings take below 1.5 µs, but some require more than 50 µs, caused by the power-up of the switchable amplifiers. Based on this knowledge, we propose a modified switching regime, in which the amplifiers are not toggled in time-critical phases, e.g., during a running measurement, so that a transition time of 1.5 µs can be reliably realized. Thus, a gain switching range of 62 dB is achieved, within which, for example, a fast automatic gain control can be realized.

Millimeter wave (mmWave) coverage is relatively limited due to high path loss (PL), that makes radio frequency planning difficult especially for the non-line-of-sight (NLOS) scenarios. In this work, we are looking to improve mmWave signal coverage in NLOS indoor scenario using passive reflectors. Measurements have been performed in L-shaped hallway using a vector network analyzer (VNA) and the path loss is evaluated with and without reflector. Experimental results show that in the presence of the passive reflector, the path loss can be reduced up to 24 dB. This type of configuration could be an economical solution to expand the mmWave coverage area. Moreover, a study is provided to compare the path loss when the reflector is placed horizontally to the path loss obtained when the reflector was placed vertically.

Current HF communication systems use sequential probing and scanning of narrowband (typical 3kHz) channels and transmissions in a single frequency band resulting in low efficiency.. In this paper we extrapolate the ideas in the HF-XL("Salamandre")-system and study a system where both the ALE and transmission procedures are fully parallel, i.e. channel probing and data data transmission can occur simultaneously in many channels on many available bands ("Channel aggregation"). An interesting problem is how distributed spectrum management for multiple links can be done in a meshed HF-network. We propose the simple "Constrained Greedy" channel allocation schemes and study the performance of a sample network in terms of throughput and message delay for various time-of-day and seasons. Result indicate that performance improvements up to an order of magnitude are possible compared to conventional systems. Finally, implementation aspects and constraints are discussed.

In this paper a simple deconvolution process for angle of arrival (AoA) retrieval is applied in a environment composed of up to five metallic poles to mimic a cluster of scatterers in the vicinity of the receiver. A measurement campaign was performed inside an anechoic chamber in two different configurations and a deconvolution process is applied to the measured signal. Preliminary results at K-band show that the proposed technique can be used to effectively retrieve the angle of arrival in a controlled environment as well as the relative power between the direct and the reflected components, that are of most importance for angular spread evaluation so that the refinement of existing and new propagation models can be achieved. In future works the algorithm will be tested within a polarimetric modelling of the propagation channel and will also be used to obtain the angular spread (AS).

Microwave hyperthermia as therapeutic modality in oncology can be the next breakthrough technology if translated properly to the clinical practice. For deep-seated tumors such as bone cancers, antennas and radiating sources fails in achieving therapeutic temperatures without overheating healthy tissues. In this framework, magnetic implant to be used as thermoseeds exposed to a several kHz magnetic field were studied. So far, the possibility of using magneto-dielectric biocompatible implant for performing microwave hyperthermia was not studied. In this work, we propose a simplified monodimensional electromagnetic model to study the propagation in a multilayer structure by means of the wave-amplitude transmission method. The model is aimed at finding suitable properties of the bolus, to be used as matching medium, while determining a set of working frequency. Then, we investigate the temperature evolution to determine, preliminarily, the feasibility of this innovative treatment modality.

A method to obtain the three-dimensional (3D) model of a hand for an antenna-hand interaction analysis of a mobile phone is presented. The radiation and reception performance of millimeter-wave signals is more susceptible to intervention by a user's hand than that of legacy below-6 GHz radios. Hand models representing a wide range of natural handgrips of mobile phone users are therefore essential. The 3D modeling is based on the photogrammetry using a video footage of a hand. Multiple 3D models of natural handgrips can be obtained with reasonable efforts. The radiation performance of a canonical antenna array implemented into a mobile phone sized chassis is evaluated using a developed series of 3D hand models, showing the uncertainty of repeatable antenna-hand interaction analyses.

Fat intra-body communication (Fat-IBC) is a novel concept of communication through the low-loss fat tissue layer of the body. This new data transmission approach is promising for the implementation of wireless, in-body, bidirectional Brain-Machine-Body connectivity, which will profoundly impact different fields, such as brain implants with read/write capability and human-like artificial sensors and limbs. In this paper, we apply an evolutionary algorithm combined with a full-wave electromagnetic solver to optimize a flat epidermal antenna, to improve the radiation coupling into the body and favor the signal transmission in the subcutaneous fat layer. The application of this method to a skin-fat communication channel shows satisfactory results when both the antennas of the link are considered and materials with high relative permittivity are used. A good radiation coupling into the body is observed, and transmission losses lower than 5 dB/cm are achieved.

In this paper, a circular polarization based wireless power transfer system is proposed for implantable medical devices (IMDs). Initially, a sequentially rotated left-handed circular polarization (LHCP) array operating at 2:4 GHz is designed for transmitter. Similarly, for receiver a miniaturised LHCP implantable antenna is designed inside a skin box to develop the WPT link. To improve the power transfer efficiency (PTE) of the WPT link a parasitic patch is placed near the receiver antenna. Parasitic patch improves the transmission coefficient by 8 dB thereby increasing the PTE by 6:7% for separation distance of 100 mm between transmitter and receiver. It is also verified that the proposed WPT system is insensitive to the angular rotation and lateral shift of the transmitter while keeping the receiver stationary. Finally, the specific absorption rate (SAR) of the implanted device is evaluated to ensure the safety limits of the proposed system.

Modular, passive and static metasurfaces are employed for the realization of a smart electromagnetic skin, a device embedded in the facade of buildings aimed at improving the communication performances through the intelligent reflection of the signal towards otherwise "blind" areas. The proposed design methodology considers an admissible surface area on the building facade and divides it into tiles (i.e., the minimal sized building blocks of the smart skin). A binary multi-objective genetic algorithm is then paired to the analytical model of the smart skin to optimize its layout (i.e., the tiles position and number), in order to satisfy a desired field threshold inside specific areas under consideration in the urban scenario. The final result is a Modular Reflecting Smart-Skin (MRSS) design methodology capable of providing an entire set of solutions, each one offering a trade-off between the complexity of the MRSS and the coverage of the blind area.

The LoRa framework has been recently proposed to foster search and rescue (SaR) missions in mountain environments. The target to be rescued could wear a LoRa radio embedded in a safety helmet so that an unmanned aerial vehicle (UAV) can localize it based on the transmitted signal strength. However, radiohelmet-to-UAV links in a real mountain area have never been characterized. This paper reports measurements of the excessive aerial path loss (PL) seen by a UAV overflying a mountain canyon to derive an equivalent model with the final aim of applying signal-strength-based localization. The angle-dependent fitting well describes the excessive aerial PL, and, despite the iced canyon's walls, no significant seasonal difference in the PL is experienced.

n fifth-generation millimeter-wave mobile terminal communications, the user body blockage will significantly shadow the radiation pattern and severely affect communication performance. In this work, the antenna is moved on the mobile handset to find a suitable position to suppress the user shadow. The investigation is conducted with the user in data mode. The shadowed antenna power ratio and shadowed cumulative distribution function are used to characterize the user blockage. Both simulations with whole-body phantom and measurements with the actual user were conducted to validate the results to provide a large degree of repeatability. A significant improvement can be confirmed when moving the antenna to the top of the handset plane than the bottom. An average of 7dB in simulation and 5dB in measurement in SAPR can be improved. The proposed method can be applied in the 5G handset antenna construction to reduce the deterioration caused by the human blockage.

Pyramidal absorbers used in anechoic chambers are one of the primary components in the measurement and performance assessment of antennas. To achieve absorbers with predefined specifications, optimum design and best material selection is an indispensable requirement. The proper material for fabricating an absorber has often been selected based on heuristic and intuitive approaches. Here, we introduce a process to find the most suitable electromagnetic material properties for achieving a target performance in an absorber with certain geometry. The method is based on using full-wave numerical simulations to obtain lines of equal absorption in the complex plane for material permittivity at certain frequency points. By locating the permittivity of available materials in the obtained plots, the best material to fabricate the absorber of interest is found. The example of 60-inch absorbers is taken into account, and the best carbon loading for fabricating such an absorber is gained through the developed process.

In this paper, the trade-off between the quality of the plane wave spectrum synthesized in the test zone of the hybrid over-the-air (OTA) chamber and factors affecting the dynamic range of this measurement system is investigated. The hybrid chamber performance is compared to a plane wave generator (PWG) in free space. The performance evaluation is focused on the field radiated into the test zone (TZ) while maintaining its quality according to 3GPP specification. It is demonstrated that a good quality can be achieved for the synthesized plane wave spectrum.

This paper investigates the characterization and calibration procedure of the hybrid over-the-air (OTA) measurement chamber. We present a prototype of the hybrid chamber and analyze its capabilities to generate a plane wave spectrum in practice. A planar field scanner is used to acquire the embedded element fields of the chamber array for test zone (TZ) synthesis in post-processing. The repeatability of the field acquisition is evaluated. It is shown that the synthesized TZ meets the 3GPP specifications for TZ field variations for plane wave generators (PWG) in the presence of acquisition imperfections.

In wireless systems, the realised characteristics of antennas in their operational environment are of major interest. This is especially true for wireless remote-control systems in combination with unmanned aerial vehicles (UAVs). In this paper we discuss measurement-based evaluations of a commercially available multi-band long term evolution (LTE) antenna mounted to the fuselage of a UAV. In comparison to the same antenna operated without the UAV, we observe an impact on antenna impedance as well as shadowing effects caused by the geometry of the UAV. Both lead to a reduced performance of the antenna and subsequently a reduction in communication reliability and range may be expected.

This paper introduces a novel approach for the measurement of time averaged Specific Absorption Rate (SAR) for multiple emitting antennas. The proposed approach is based on the use of the phase information of the E-field phasor given by radiofrequency vector SAR measurement system, for the retrieval of the instantaneous input RMS power injected in the emitting antennas from a small number of SAR measurement points. The approach is presented for the case of two emitting antennas. Numerical validation was performed in the case of two dipole antennas radiating coherently at a single frequency.

Ray-tracing methods can be applied to evaluate the wave propagation in anechoic electromagnetic environments, in order to improve measurement concepts. The accuracy of the data obtained from such a chamber model depends crucially on the modeling of the microwave absorbers. Often the scattering off the absorbers is simplified by specular reflections, ignoring the actual direction dependent scattering properties of the absorbers resulting from their geometry, arrangement, and material. In this paper, the scattering of 18" absorbers with pyramidal and wedge geometries is analyzed and expected scattering patterns are described. Based on an existing shooting-and-bouncing- rays software, a simulation approach is introduced and used to relate the analytical findings with results of measurements of the angle-dependent reflectivity. In addition to the primarily specular reflection for wedge absorbers and scattering in many directions off the pyramidal absorbers, the results show that nearfield effects influence this scattering pattern, as confirmed by the simulations.

In wireless communication systems, in order to respond to the perception of risks related to electromagnetic field exposure and allocate radio resources, the estimation of the received power and exposure map is an essential task and a challenge. This paper proposes an algorithm for estimating electromagnetic field exposure maps using U-net architecture based on convolutional neural networks. The power map estimation is transformed into an image reconstruction task by image color mapping, where every pixel value of the image represents received power intensity. The designed model learns wireless signal propagation characteristics in a realistic indoor environment while considering various positions of the Wi-Fi access points. Results show that indoor propagation phenomena and environment models can be learned from data producing an accurate power map to measure the electromagnetic field.

Numerical dosimetry is an essential procedure in designing and optimizing propagating EM-devices that confirm to the recommended limits of Specific Absorption Rate (SAR). However, as frequencies go higher, the complexity of the computational problem increases substantially. Moreover, the high heterogeneity of the human body and the uncertainty in its tissues properties add to that complexity. Furthermore, as the numerical domain becomes very large, the impact of numerical dispersion becomes more visible leading to decrease the mesh-size even more. This article sheds some light on the 3D-simulation of such computational problems, and revisits the necessary mesh-size condition that ensures convergences and accuracy of results. Comparisons between FIT and TLM methods are presented to show the speed of convergence for both methods.

In the vision of smart railways, a seamless high-data-rate and dependable wireless connectivity both for communication and sensing will be required. It is of primary importance to generate realistic channel data in order to do properly all the application layer end-to-end tests for all the relevant use cases that will be enabled by these wireless systems in railways. In this talk, we identify the major challenges and present the state-of-the-art solutions towards realistic channels of smart railways, especially for high frequencies, such as the millimeter-wave and THz bands. Moreover, future research trends are pointed out towards a thorough understanding of the propagation and wireless channel characteristics to support the design and evaluation of future smart railway wireless sytems.

The study of stratified media, defined as layered configurations of material substrates, is of paramount relevance in many scientific and technological areas like Acoustics, Geophysics and Lightning. In Electromagnetics, the first treatment of these problems is due to Arnold Sommerfeld who, more than one century ago, solved the most basic of all stratified media geometries, i.e. the two semi-infinite media problem. In doing so, Sommerfeld developed the fundamentals of a mathematical method, which is now known as the spectral domain approach (SDA). After many decades of latency, the analysis of stratified media using SDA knew a strong regain of interest, due to the introduction of printed technologies (microstrip and striplines) and the development in the 70s of the first planar antennas. Nowadays, SDA is used in many other areas of Electromagnetics, like Ground Penetrating Radar, satellite-based Remote Sensing and Optics&Photonics. This tutorial will review the stratified media problem and its formulation through the so-called Sommerfeld Integrals. Some tricky points, like complex square roots definitions, the relevance of a ground plane at infinity and the existence of a Sommerfeld pole (and hence of a surface wave) will be discussed. Numerical techniques will be briefly discussed and used to illustrate some recent discussions in the literature about the behavior of electromagnetic fields as a function of radial distances and of elevation angles (radiation patterns).

In this talk the quest for the "final" expressions for the energy stored in a radiator is overviewed. First, the several forms of power and energy that have been defined and used in electromagnetics over the last 100 years are briefly summarized, and their most important characteristics are discussed. In a first step, frequency domain is considered. Starting from two power balance equations, a field based reactive energy is formally defined and compared to the numerous "definitions" already available in literature. Then the concept of recoverable energy is introduced. The differences with reactive energy are pointed out. Moving to time domain, it is possible to write unifying expressions generalizing the concept of reactive energy. It is shown that recoverable energy is just a special case for a specific current evolving in time. Illustrative examples are given where these energies can be used to solve practical problems. The paper clearly illustrates that the concept of stored electromagnetic energy is still not well-understood when a radiator is involved.

Advanced electromagnetic surfaces (AESs) comprise a spectrum of artificially engineered surfaces for manipulating the temporal and/or spatial dispersion of electromagnetic waves, and include structures such as reflectarrays, transmitarrays, frequency selective surfaces, polarizers, and most recently, metasurfaces / metagratings. The design of such surfaces can be separated into two steps: a macroscopic step, where the surface parameters required to achieve particular manipulations of the incident field are determined; and a microscopic step, where the geometric structure of the underlying unit cells or meta-atoms is determined to realize those properties. This talk will review recent developments in systematic design techniques for both steps. In particular, synthesis methods will be described for carrying out the macroscopic step, particularly for spatially-dispersive AESs used to implement specific radiation patterns. Subsequently, a variety of techniques for solving the inverse design problem associated with the microscopic step will be presented, with emphasis on recently developed techniques based on machine learning. A selection of AES designs developed based on the proposed techniques will be presented, including experimental demonstrators of several metasurfaces.

This contribution presents the design and preliminary results of an electromagnetic wave propagation experiment at G band. The research activity, resulting from the collaboration between Politecnico di Milano and the Huawei European Microwave Centre in Milan, focuses on the design, integration and installation of a custom G-band 325-m terrestrial link connecting two buildings in the university campus. The unidirectional link carries an unmodulated beacon signal at 261 GHz, which allows investigating with high accuracy the atmospheric impairments affecting the propagation of electromagnetic waves. To this aim, the signal attenuation, inferred from the received power, is correlated to the ancillary data measured by the collocated rainfall sensor. The preliminary results reported indicate quite a significant impact of precipitation, which needs to be further studied using the information on the microphysical properties of rainfall.

In this paper, we compare measurements of the millimetre-band propagation channel at 60 GHz using Fujikura prototype communications equipment in an indoor office environment with those obtained using a Keysight N9042B Signal Analyser and simulations performed using Ray Tracing techniques. Based on the IEEE 802.11ad standard, the Fujikura equipment establishes a wireless network to measure the 60 GHz propagation channel. Wireless Insite software has been taken into account to emulate the scenario, where the simulation considers the three-dimensional environment model and proper material electromagnetic parameters. The experimental and simulation results include the Received Power, SNR, and Throughput. We show that there is a good agreement between experimental and simulation results. In addition, we have also verified that the measurements made with a horn antenna connected to the Signal Analyser, present a worse behaviour when there is Non Line of Sight with respect to the results obtained with Fujikura equipment.

The 6th generation mobile communication system requires the realization of ultrahigh speed and high-capacity communication. To meet the diverse communication requirements of individual users, it is desirable to use the terahertz band for communication between user terminals and peripheral devices. For the design and evaluation of stable systems, it is necessary to clarify the propagation characteristics of the blockage loss. In this paper, we investigated the propagation characteristics of the blockage loss for the human body at frequencies up to 110 GHz. Based on the experimental results, we clarified that the characteristics of the blockage loss due to a part of the human body follow the existing model. In addition, the variation in the blockage loss for a stationary human body is attributed to differences in the propagation path length produced by slight movement of the human body, and an estimation method for such a range of variation is presented.

In this paper we investigate the impact of the use of Transmitting Reconfigurable Intelligent Surfaces (T-RISs) on the indoor millimeter wave (mmWave) radio channel characteristics. To this purpose, two measurement campaigns were conducted by employing a T-RIS array and a virtual cubic array (VCA). The multipath component extraction was performed to embed the TRIS based antenna pattern and evaluate the effect on large-scale parameters such as the path loss, delay and angular spreads.

In this paper, we investigate the reflection properties of different interior surfaces in the 92-110 sub-Terahertz (THz) band. The measurements are conducted in an indoor environment by placing the surface in a specular configuration between the Transmitter (Tx) and Receiver (Rx) and collecting a large set of data by offsetting the Tx and Rx in parallel to the surface. The measurements were performed using an Agilent N5230A Vector-Network-Analyzer (VNA). Particularly, we present a statistical analysis in the frequency domain to show how frequency selective each surface is and how constant this behaviour is across the whole data set. We introduce the Power-Delay-Profile (PDP) in the delay domain to characterize the multipath behaviour of the channel and calculate the RMS delay spread. The measurement results provide a good insight for future propagation work to be done for the development of future indoor communications systems at sub-THz frequencies.

Several services associated with satellite on the move and 5G applications are populating the K and Ka frequency bands. Beam forming networks are crucial components for achieving the necessary beam flexibility and agility of these systems. The Rotman lens is being widely investigate as a cost-effective solution for overcoming the main limitations of other types of beam forming networks, namely bandwidth, complexity, and size. One of the main design challenges is obtaining broadband transitions for the array and beam ports. In this work, we used a standard K/Ka double ridge (WRD180) for interfacing with the Rotman Lens. The main motivation for this choice is the wide bandwidth, compatible with the K/Ka satcom frequency bands, and the use of air/vacuum propagation medium in the parallel plate waveguide section to avoid dielectric losses associated with microstrip implementations. We present a design capable of fully exploiting the ridge waveguide bandwidth with wide beam scanning, outperforming previous works. The presented design consists of a 13×7 Rotman Lens with a scanning range of ±50 degrees operating between 16 and 40 GHz, validated through full-wave simulations.

In this work a synthesis technique for designing sparse phased arrays of large size is presented. The procedure is based on an iterative convex optimization algorithm, also known as compressive sensing, which is straightforward to implement and efficient in terms of computational cost. It is capable of producing a layout with a significant reduction of active elements for predefined performance. Due to its effectiveness, it can also be employed for the optimization of large arrays. The capabilities and versatility of the algorithm are illustrated by different case studies. In particular, the possibility to reduce by 45 % the number of elements in a large array is shown in details.

This paper presents an efficient design of an SIW horn antenna array for upper part of the Ka-band. The array is formed by a corporate network in substrate integrated waveguide (SIW) technology which feeds eight SIW horn. Impedance matching between each SIW horn and the free space is carried out by using a SIW-to-air transition that efficiently matches with the rest of the antenna elements. The array feed is based on an end launch connector over grounded coplanar-waveguide (GCPW) technology that makes an efficient transition to SIW. The corporate network has two-by-two electromagnetic (EM) field splitting levels through the use of H-plane T-splitters and waveguide bends. Thus, an in-phase and equal power symmetrical array structure is achieved from 34 GHz to 41 GHz (18.6% of bandwidth). The simulated results present a high stable gain of 14 dBi in the H-plane along the whole frequency range.

A novel partitioning scheme based on Penrose tessellation subarrays has been proposed for phased array design. More in detail, the radiating elements of a phased array arranged on a regular and periodic lattice are grouped into irregularly-shaped tiles by exploiting the features offered by the aperiodic Penrose tessellation. The preliminary results reveal that the novel array architecture ensures a remarkale reduction of the Transmit/Receive modules without compromising the performance in terms of scan angle and peak side lobe level.

The paper deals with the diagnostics of realistic array antennas by exploiting phaseless measurements. Provided the number of faults is not small with respect to the overall number of elements, the proposed approach allows performing the diagnostics whatever the kind of radiating elements even if the measurement surface is located in the near-field zone. Despite the high non-linearity induced by the adoption of phaseless measurements, the underlying optimization problem can be cast as a Convex Programming one taking decisive advantage of the Compressive Sensing theory. Examples concerning 1-D array diagnostics are given for both cases of ON-OFF and phase faults.

A compact monopole antenna for ultra-wideband (UWB) and beyond applications has been proposed. The radiator is based on the monopole topology. The super-wideband behavior has been achieved using a combination of spline-based modifications applied to the driven element, as well as utilization of a tapered feed and a slot-modified ground plane. The electrical performance of the structure has been tuned using a numerical optimization algorithm. The proposed design features reflection below the level of -10 dB within 2.8 GHz to 30 GHz range, as well as a footprint of only 404 mm 2 . The proposed structure has been compared in terms of bandwidth and size with the state-of-the-art antennas from the literature. The numerical results are supported by measurements of the fabricated antenna prototype.

The metasurface inspired antenna chip developed by the KIT EOE Laboratory (MACKEY, RFID 920 MHz) is an electrically small antenna that is sufficiently robust to metal objects. However, there have been demands for miniaturization of the available model, which has a length of 200 mm at 920 MHz. Therefore, a new model called the MACKEY type H (RFID 920 MHz band) is proposed herein and is miniaturized to the size of a card. The type H antenna can extend the current path in a meandered manner through slits cut along the long sides of the grid plate. This paper presents the characteristics of the MACKEY type H antenna and its measurement results.

In this paper, a miniature frequency-agile antenna is presented. The antenna is of balanced structure, composed of a driven element fed differentially, and a parasitic loop element loaded with a varactor. The antenna maximum dimension is 28.8 mm, electrical size ka=0.3, designed to operate near 1000 MHz. A prototype is fabricated and measured to validate the simulated performances. The measurement results show continuous eight states tunable bandwidth of 5.05% at the central frequency 1010.5 MHz corresponding to -10 dB |S11| maximum-acceptable input reflection coefficient, and a radiation efficiency of more than 34% over the tunable bandwidth.

In this paper, an orthogonally polarized antenna with a small diameter and low profile is proposed for mobile communication. The proposed antenna is composed of a Halo antenna loaded with two parasitic elements as the horizontal polarization element and dipole and sleeve antennas as the vertical polarization elements inside the Halo antenna. The simulation results show that the proposed antenna with the sleeve antenna has a relative bandwidth of 6.9 % (VSWR ≤ 2) and an isolation between polarizations of about 30 dB within the operating frequency. In addition, the antenna diameter and height of the proposed antenna are 0.14λ0 and 0.49λ0, respectively, and a low profile orthogonally polarized antenna is obtained.

There are some challenges in effectively producing low frequency electromagnetic waves, such as the need of large scale antennas, particularly for submarine communications. Due to hardness and challenges of building low frequency antennas, some solutions are provided. Using acoustic wave is one of solution which is the most common alternative for low frequency electromagnetic waves. A new solution which is in the researching level, is known as Mechanical Antenna. This sort of antenna which enables us to propagate low frequency electromagnetic waves, has the advantage of being extremely small in comparison with common electrical antennas. Some efforts have been done on analyzing and testing this type of antenna in order to estimate the pattern and propagated power of mechanical antenna. In this paper, initially parameters affecting the power radiated in past researches has been investigated and a novel solution is provided in order to increase the propagated power.

Heart valve replacement is one of the most common life-saving surgery procedures. Although valve prostheses can restore heart functionality and life expectations, they often suffer from to structural deterioration that can lead to the failure of the implant. Conventional diagnostic tools include minimally invasive and operator-dependent examinations. Alternative remote monitoring approaches would be extremely useful for evaluating the valve status from outside the body and for early detecting possible failure events. In the framework of Health 4.0 this paper proposes a method to extract an antenna mode out of an aortic valve so that it can be provided with communication capability without any need of battery. By minimal modifications of the mechanical layout, the valve integrates an RFID sensing IC capable to passively, sample the temperature in the surrounding tissues and communicate with an external reader. Numerical simulations and early experimental tests demonstrate the feasibility of the communication link.

Abnormal breathing can be a symptom of an unhealthy status. Conventional diagnostic exams involve cumbersome and intrusive instrumentation that are overall uncomfortable for the user. Ultra High Frequency (UHF) Radio Frequency IDentification (RFID) devices, instead, enable non-invasive wireless monitoring of respiration by means of epidermal antennas with embedded temperature sensors. Two sampling points in the same device could be useful to independently measure the respiratory flow of the two nostrils, which are known to work differently. At this purpose, this paper proposes a two-channel flexible epidermal sensor for the bilateral monitoring of nasal breathing based on temperature measurement. It compactly adheres on the prolabium, and comprises two coupled T-match asymmetric dipole antennas whose ICs are placed at the exit of the nostrils. The sensor can be read up to 60 cm. Experimental tests on some prototypes demonstrated that, thanks to negligible cross-sensitivity of the two ICs' temperature data, the breathing rate can be accurately estimated independently for the two nostrils.

The viable and safe application of wireless power transfer for powering bioelectronic implants requires understanding the wave propagation in heterogeneous and dispersive media, the electromagnetic exposure assessment, and the optimum design of the system parameters to achieve a trade-off between efficiency and specific absorption rate levels. Therefore, based on the case study of a wirelessly charged deep-implanted pacemaker, a parametric analysis on the transmitter dimensions and electromagnetic properties is carried out to achieve such a trade-off. The results show that the system reaches the maximum efficiency without increasing SAR levels when the transmitter is composed of an electric source, an air-like substrate, and a superstrate matched to the wave impedance in the skin with a thickness of half the wavelength in this medium. Furthermore, this configuration is compared to a magnetic counterpart, and the reasons for its suboptimal performance are investigated in terms of near-field, reflection, and attenuation losses.

Radiofrequency finger augmentation devices (RFADs) are hand-worn systems based on the RFID (radiofrequency identification) that can sense the objects touched by the wearer while preserving the free-hand gestures. A pressure-sensing R-FAD could be useful for applications in physiotherapy, orthopedy, and even more with the upcoming Tactile Internet (TI) paradigm, which aims at extremely low-latency communications and the transmission of human senses through the internet. This paper proposes a pressure-sensing fingertip tag that is manufactured using a robust conducting thread. Following preliminary tests on a prototype, the tag was demonstrated sensible enough to swiftly detect small discontinuities of the human body, like the back-hand knuckles.

This paper discusses a method to improve the resolution of microwave biomedical sensors. Usually, the frequency response of these devices is relatively wide as compared to its ideal shape. Furthermore, only a finite number of its samples can be acquired in the measurement stage. Accordingly, to have an accurate estimate of the resonance frequency, high performance systems with high sensitivity are required. Thereafter, in order to overcome these drawbacks, an iterative algorithm is presented which aims at sharpening the microwave sensors response. The algorithm assessment is performed on measured data referred to a real scenario, which is inherent to return loss measurements of a microwave patch antenna submerged in a water-glucose solution with various glucose concentration levels.