This paper presents the first interdigitated finger capacitors fabricated using the ultra-precise deposition (UPD) printing system by XTPL to the best of our knowledge. Various lengths of the individual fingers are designed, fabricated and compared. The small structural sizes that can be achieved using the UPD technology allow a reduction of parasitic effects resulting in an increase of the self resonant frequency (SRF) and high bandwidths. In addition different dielectric materials are added on top of the printed structures to increase the capacitance. All capacitors are printed on a fused silica substrate, that is prepared accordingly to enable a smooth transition between a coplanar waveguide (CPW) feed and the printed paths. This paper demonstrates the potential of the UPD printing system for printing passive circuit components, particularly interdigitated finger capacitors.

In this research, we present an electronic near-field sensor designed in 180 nm complementary metal-oxide-semiconductor (CMOS) technology, specifically tailored for terahertz dielectric spectroscopy. Our sensor utilizes a unique on-chip detection mechanism, which allows to probe the dielectric properties of materials in aqueous solutions. We have achieved superior sensitivity values, positioning our sensor at the forefront of terahertz-related techniques.

A compact millimeter-wave (mm-wave) amplifier is presented in this paper. The amplifier consists of three cascode stages with a single-ended configuration and is implemented in a 28 nm CMOS technology. In order to achieve the demonstrated compact core size, the input, output, as well as two inter-stage matching networks of this circuit were all realized with only a single inductor. Without using any other passive components, the core size of this three-stage amplifier is shrunk to 0.29 mm × 0.28 mm = 0.08 mm2. With a total dc power dissipation of 60 mW, this amplifier exhibits a peak gain of 15.9 dB at 29.5 GHz with 9 GHz 3-dB bandwidth (BW) from 25.5 to 34.5 GHz. Meanwhile, the measured maximum output 1 dB compression point (OP1dB) is -2.75 dBm at 29 GHz, and the minimum in-band noise figure (NF) is 6.4 dB at 34 GHz, including around loss of the feeding lines both at the input and output side. Overall good agreement between simulation and measurement is observed.

In this paper, a linearity enhanced millimeter-wave (mm-wave) Gallium Nitride (GaN) monolithic microwave integrated circuit (MMIC) power amplifier (PA) is presented. The linearity of the proposed amplifier is improved by using the amplitude to amplitude modulation (AM/AM) distortion compensation and the amplitude to phase modulation (AM/PM) distortion cancellation between the driver-stage and the power-stage transistors. For proof of concept, a 26-to-28-GHz GaN MMIC PA was designed using a 120-nm GaN on silicon carbide high electron mobility transistor process. The fabricated amplifier achieves a saturated power of around 30 dBm, with the AM/AM distortion of less than 3-dB and the AM/PM distortion of smaller than 5° from 26 to 28 GHz. The corresponding power-added efficiency (PAE) at saturation is 32.3%-35%.

We present voltage control oscillators based on a differential Colpitts oscillator topology with optimized emission frequency at the fundamental harmonic in a 130 nm SiGe BiCMOS technology. The radiation is out-coupled through the substrate side using a hyper-hemispheric silicon lens. The source is optimized for 250 GHz and radiates up to 0.325 mW of propagating power. We present an experimental study of the dynamical properties of electronic oscillators subjected to feedback radiation with its application for reflection-type coherent imaging.

This work presents power amplifiers with integrated features like DC supply switch for reducing the power consumption in receive mode of an RF front end (RFFE) module and RF switch for compact RFFE module design. Two 28–32 GHz power amplifiers, one with only DC supply switch and the other with both DC supply switch and RF SPST switch, are designed and fabricated using 0.15 µm GaN-on-SiC technology. The PA with DC supply switch shows a measured small-signal gain of 11–12.7 dB at 28–32 GHz, Psat of 31 dBm and PAEpeak of 24% at 30 GHz. The PA with DC supply switch and RF SPST switch, on the other hand, exhibits a measured small-signal gain of 9.2–11.6 dB at 28–32 GHz, Psat of 29.5 dBm and PAEpeak of 15% at 30 GHz. In the receive mode, the measurements show a power consumption of only 20 mW (instead of 2 W in transmit mode), port-to-port isolation of more than −27 dB and S22 higher than −3 dB at 28–32 GHz highlighting the effectiveness of integrated DC and RF switch.

Recently satellites in low earth orbit (LEO) used for satellite communications (satcom) are entering a period of growth. LEO satellites are capable of operating their thruster systems to adjust their attitude and altitude in orbit. A recent development for thruster system uses compact microwave-discharge ion or Hall thruster technology with main advantage being the utilization of noble gas or water-vapor over traditional combustible fuels. Hence, the thruster system can operate with greater safety, cost-effectiveness, and a size reduction compared to other type of thrusters. Massive satellite constellation employing water vapor systems based on LEO satcoms could benefit during deployment and normal operations. The thruster system consists of an oscillator-stage, amplifier-stage, and a microwave-discharge ion thruster. To realize the advantages of a water-vapor based system, it is necessary to develop a high efficiency microwave power source (MPS). We developed a MPS with a dielectric resonator oscillator (DRO) and single class-F power amplifier with 10-W-class GaN power transistors. The oscillator can generate 1 W output during the amplifier-stage requires 1 W (30 dBm) input to operate and outputs 10 W microwave power at the most optimal power efficiency. In this report, we explain the development of 10-W-class MPS which is a 41.76 dBm maximum output at 4.2074 GHz with a system efficiency of 46.65%. We also detail the environmental evaluations complied with space standard from the SMC-S-016.

The dynamic behaviour of RF power splitters has great impact in the behavior of dual-branch RF power amplifiers (PAs) such as Doherty power amplifiers (DPAs). Recently, we have introduced a structure as a nonlinear power splitter which has the capability to change the power ratio based on the terminal impedances in the output ports. In the previous work, we discussed the amplitude response of this new structure and how we can deliver more power to one branch or vice versa in dualbranch configurations. But, for using this structure in the Doherty amplifier, the phase response of this structure is crucial as well. In this paper, we analyze the phase response of the standard Hybrid Branch Line Coupler (HBLC) structure and then we show that the phase response of the nonlinear power splitter has some advantages that make it easier to use in the Doherty power amplifier design. Continuing, we show some potential applications of the nonlinear power splitters for RF/Microwave amplifications.

This paper presents the design architecture, simulation and measurement result of a stable high-performance onchip signal generator system. The system consists of an ultra-lowpower Voltage controlled oscillator designed for the frequency range of 7.2 - 8.2 GHz and is interfaced with a divide-by-2 pre-scaler. The circuit generates an RF output of 3.6 GHz to 4.1 GHz with constant average output power and phase-noise (PN). The minimum current consumption of VCO core is 1.05 mA at a supply voltage of 250 mV and a back gate voltage of 1.4 V. The back gate bias is adapted in the RF block to minimize the DC power consumption and enhance the PN and the output power.

In this paper a highly linear X-band MMIC mixer implemented in a 0.25 um GaN HEMT technology is presented. The mixer is based on a single-balanced resistive architecture using a pair of symmetrical 4 x125 um GaN HEMTs. A novel minituarized half-wavelength hair-pin type of balun creates the balanced LO signal to be fed to the gates. A lumped-element diplexer network is used to separate the IF and RF signals at the drains. The fabricated MMIC mixer demonstrates a 6.9 dB conversion loss at 10 GHz with an LO power of +24.6 dBm and a bandwidth from 7.8-12.2 GHz. Over the same bandwidth the single-tone second and third-order spurious responses are below -66 dBm and -98 dBm, respectively, at an RF input power level of -10 dBm. The experimental results furthermore show that the two-tone third-order input intercept point (IIP3) reaches 30 dBm at an applied LO power of +24.6 dBm.

Massive MIMO is a key 5G technology and will be even more important for future generations of cellular standards such as 6G. The system performance improvements offered by this technology and the possibility to develop larger antenna arrays for new frequency bands pave the way to the future deployments of extremely large multi-antenna systems. This paper provides an analysis of the actual EMF exposure levels from extreme massive MIMO active antenna array systems that are targeted for 6G mobile networks in the 7-15 GHz frequency range. Various antenna array dimensions have been investigated, from a 12×8 array of 192 antenna elements to a 24×16 array with 796 antenna elements. Modelling studies have been performed at 10 GHz. The actual maximum approach has been implemented as recommended in IEC 62232:2022. The modelling results provide a range of power reduction factors (FPR) from -7.1 dB to -10.7 dB with increasing antenna array size.

This article introduces a pioneering development in wireless communication technology, presenting a novel compact Semi-Elliptical Shaped Slotted (SES) ultra-wideband (UWB) Multiple-Input Multiple-Output (MIMO) antenna having dimensions 15 x 30 mm2, it is designed using HFSS software. Two slots were incorporated on the patch elements to generate the notch bands at X-band and Ku-band. A slotted parasitic strip engraved on the Partial Ground Plane (PGP) to generate the third notch at Ka-band and to enhance the isolation. The proposed design achieved the operating bandwidth of 38.15 GHz with triple notch characteristics. It also achieved the reflection coefficient (S11) of -28.26 dB at 17.28 GHz frequency and isolation of ≤ -17 dB for the entire ultra wideband. It also achieved the gain of 8.45 dBi with good radiation pattern.

The present article introduces a novel wide-band, open-ended monopole antenna, supplemented by fabrication. To attain a broad impedance bandwidth, an open-ended slot is intricately etched onto the radiating element. The design employs an FR4 substrate with a dielectric constant of 4.4. The resultant antenna covers a diverse frequency bands including a wider notch band (3.97 to 8.13 GHz) with a center frequency of 6.05 GHz. The notch band is achieved by etching an L-shaped slot on the partial ground plane. The proposed monopole structure achieved the maximum S11 of -31.17 at 3.07 GHz and high gain of 3.05 dBi. The proposed wideband antenna design is appropriately suitable for L (1-2 GHz) and S (2-4 GHz) band applications.

In this research paper, a novel and compact four-port Slotted Circular Ring (SCR) Ultra wideband (UWB) MIMO antenna is proposed, featuring an aperture area measuring 40 x 40 x 1.6 mm³. This antenna design incorporates notch band characteristics and high isolation. The primary focus of this research is to develop a UWB MIMO antenna with minimized design complexity yet offering high performance, which emphasizes the concerted effort to enhance communication efficiency while minimizing the intricacies inherent in the design and implementation of UWB technology. Hexagonal structure merged with SCR enhanced the impedance bandwidth from 13.66 to 14.31 GHz, which is suitable for C-band, X-band and Ku-band applications. It covered the UWB from 4.19 to 18.5 GHz with a notch at C-band (5.06 to 5.64 GHz). In order to obtain isolation >25 dB, neutralization lines (NL) are placed between the antenna elements. Acceptable findings were obtained when evaluating the antenna's performance in terms of diversity characteristics such as ECC, TARC, and DG. The maximum return loss (|S11|) of 24.94 dB is achieved at 4.77 GHz. The measured results of the fabricated prototype and the simulated results are in good agreement.

This article presents an optimized dual-polarized transmitarray antenna (TA) designed for MIMO applications at the Ka-band, capable of switching beams in two directions. The antenna aperture uses a small unit cell with three layers of Taconic RF-35 dielectric substrates, which can be easily fabricated using PCB technology. The unit cell achieved a 360-degree phase shift and a transmission magnitude exceeding -0.4 dB at 28 GHz. We used nine dual-polarized patch antennas in a cross shape, each with a 10.5 dBi gain at 28 GHz, to switch the beams in two directions without changing the feed location. We optimized the phase distribution in the TA aperture and adjusted the feed antenna's F/D and tilt to achieve a high-gain antenna with low-gain roll-off during beam switching. The fabricated TA exhibited excellent agreement with the full-wave simulation results. It achieved ±15 degrees and ±30 degrees beam tilts in the x- and y- directions, with less than 0.8 dB gain roll-off for both polarizations. Transmitarray antennas have emerged as promising solutions for various wireless communication systems due to their ability to combine the advantages of optical theory and antenna array techniques, resulting in low-profile, high-radiation efficiency designs. Dual-polarization in TAs is typically achieved through techniques such as multilayer frequency selective surfaces (M-FSS) or receive-transmit (R-T) schemes. TAs can perform beam scanning using either electrical or mechanical control solutions. In the case of electrical control, RF components such as PIN diodes are added to each unit cell to achieve tunable transmission phases by controlling the DC bias. This approach is expensive, lossy, and complex. Passive TAs, on the other hand, can only provide a fixed phase shift once their dimensions are determined. Nevertheless, the beams of the passive TAs can be mechanically steered by moving the feed source, which causes a high gain roll-off issue. This occurs when the feed source veers from the center to scan the beams in a unifocal TA with an aperture designed for the center-located feed source. In this study, we used a compact unit cell composed of three layers of Taconic RF-35 dielectric substrates, facilitating cost-effective fabrication using PCB technology. The unit cell has two circular patches in the top and bottom layers and a circular ring with four lines in the middle layer of each stacked FSS and is suitable for dual polarization applications due to its symmetry. The required 360-degree phase shift has been achieved at 28 GHz with less than 0.4 dB transmission magnitude loss. This allowed us to design a highly efficient wideband TA and optimize the antenna aperture for beam scanning. The unit cell in this design is smaller than the ones examined in the literature, which reduces the sidelobe levels in the TA by fitting more unit cells into the aperture. To realize beam switching in two dimensions, we employ a configuration comprising nine dual-polarized patch antennas arranged in a cross shape. Each patch antenna exhibits a gain of 10.5 dBi at 28 GHz, ensuring robust performance across the desired frequency band. The optimization process involves fine-tuning the phase distribution within the TA aperture and adjusting parameters such as the focal length-to-diameter (F/D) ratio and tilt of the feed antennas to mitigate gain roll-off during beam switching. By carefully optimizing these parameters, we achieve remarkable beam steering capabilities, with the fabricated TA demonstrating ±15 degrees and ±30 degrees beam tilts in the x- and y-directions, respectively, while maintaining gain roll-off below 0.8 dB for both polarizations. To validate the proposed design, extensive full-wave simulations were conducted using CST Microwave Studio software (Fig. 1). The simulations utilized a sophisticated computational setup, including a Hexahedral mesh type with high accuracy and sufficient simulation precision. The simulation results demonstrated excellent agreement with the fabricated TA, confirming the effectiveness of the optimization strategies employed. In summary, this paper introduces a novel approach to optimizing dual-polarized transmitarray antennas for Ka-band applications. Through advanced optimization techniques and innovative design configurations, significant enhancements in beam steering capabilities, efficiency, and low-profile design characteristics have been achieved. Comparative analyses with existing literature highlight the notable advantages of the proposed design, particularly in unit cell size, phase range, and efficiency. By leveraging these advancements, the proposed design holds great promise for advancing wireless communication systems, especially in the realm of emerging MIMO applications and next-generation millimeter-wave technologies.

In advanced packaging, the epoxy molding compound in electronics is growing popularity for RF interconnect technology and antenna. This promotes the need to characterize the properties of molding material over a broad spectrum to facilitate electronic design. This paper demonstrates the dielectric properties of C8 mold material over five decades of frequency using five different characterization techniques. The dielectric constant of C8 varies from 3.5 to 4 and the loss tangent varies up to 0.01 from 0.1 GHz to 10 THz.

This paper presents a broadband measurement technique for characterization of lossy dielectrics in sub-THz frequency range. The method is based on measuring only the complex reflection coefficient and does not require accurate information about the thickness of the sample under test.

mmWaves is seen to be one of the key enablers for 5G and 6G communications. However, a serious problem may be a limited link budget, especially in the indoor scenario. Therefore, in this work, the penetration of the floor and loss of material are analyzed with a series of measurements at frequencies 18-30~GHz. The measurements showed that there is a great variety of material losses which should be taken into account in Outdoor-to-Indoor or Indoor-to-Indoor models. Of six materials, the measured loss varied from 2 up to 67~dB, while the measured floor loss ranged from 31 to 49~dB depending on the frequency. The final conclusion also is that with many materials the communication may be feasible at frequencies 18-30~GHz, however, the floor penetration loss makes the communication nearly infeasible.

Characterizing material at millimeter wave frequencies can be challenging. Test engineers have to make a proper choice between many different measurement configurations depending on the sample shape and nature of the interaction with the electromagnetic wave. Many existing experimental setups are optimised for dielectric materials and the determination of the complex permittivity but only few are handling strong losses in transmission which are typical for EMI materials. In this paper, the material characterization of EMI absorbers using a waveguide-based sample fixture around 60 GHz is discussed. The attenuation constant and the wave impedance are determined under consideration of the reflections at the material interfaces of the bulk material. Best practices for RF material characterization can be deduced for this particular case.

Attenuation caused by rain poses significant challenges for millimeter wave communication systems, especially in regions with heavy rainfall. Accurate attenuation prediction is required to set realistic performance expectations and ensure robust millimeter-wave communications links for 5G networks even in challenging environments. The aim of this work is to model and optimize rain attenuation in terrestrial 5G using evolutionary algorithms. The attenuation is modelled using symbolic regression that takes rain rate, path length, and frequencies between 24.5 GHz and 86 GHz as input. Next, differential evolution is used to determine the optimal parameters that best fit the model. The model is found to predict the attenuation with minimal errors. The proposed model's performance is evaluated against the ITU-R, Crane, Da Silva and Melo models. The proposed model's accuracy and performance are further validated based on the obtained MSE, MAE and R-squared values.

In this paper, a new six-port reflectometer is proposed, which is capable of optimum operation over a wide frequency range from 1.2 GHz to 4.8 GHz with power detectors that exhibit poor impedance match. In the proposed concept the signals reflected from power detectors are redirected to matched loads, hence they do not impact the signal distribution scheme defining the measurement uncertainty. As a result, the six-port can operate equally well with matched and non-matched power detectors. The six-port reflectometer is designed, fabricated, calibrated, and used to measure complex reflection coefficients over 40-dB magnitude's range showing very good agreement with measurements done with a commercial vector network analyzer.

This paper presents a novel design of a reconfigurable phase shifter based on groove gap waveguide (GGW) technology. The proposed phase shifter consists of some GGW bends with movable pins that can change the waveguide length and thus the phase of the electromagnetic (EM) waves. The advantage of the GGW technology is that it does not require electrical contact between different parts of the structure, which enables the moving parts to slide freely without EM leakage. The proposed phase shifter is simulated using CST Microwave Studio and shows a good performance in terms of reflection coefficient, insertion loss, and phase shift of 915°.

The paper presents the results of theoretical considerations, supported by the results of simulations, concerning the implementation of a miniaturized S-band diplexer based on SIR (Stepped-Impedance Resonators). The project is the next stage in the development of S-band diplexers, manufactured by WiRan. This time, the focus was on minimizing the dimensions and weight of the device and achieving high far-out-of-band-rejection (FOOBR) of 2nd-5th order harmonics. At the same time, efforts were made to keep the remaining electrical parameters attractive, thus meeting the project requirements set by European Space Agency. The choice of the diplexer technique (SIR with Teflon disc - PTFE) was dictated by the excellent FOOBR results obtained in this type of solutions. According to the assumptions, the project is to be implemented at least at the Technology Readiness Level 6. Nevertheless, efforts will be made to ensure that the project finally ends at TRL 9. In this article a band pass filter is presented being a demonstrator of technology to be applied in final diplexer with extraordinary spurious-free performance of up to 5 times the edge frequency of TX filter and very good multipactor performance, which is critical aspect in space applications. Although high quality factor is maintained, the resulting geometry allows for compact realization of diplexer.

This study presents the design of Acoustic-Wave-Lumped-Element Resonator (AWLR)-based filters using the classical cascade synthesis approach as a simpler and more practical method instead of the coupling matrix (CM)-based synthesis approach. The classical cascade synthesis approach is used to design hybrid bandpass (BP), bandstop (BS), linear phase filters, and BP-BS diplexers using commercially available identical SAW resonators leading to bandwidths wider than all-AW filters with higher Q-factors. It is shown that simple circuit transformations enable the quick design of such hybrid filters.

A novel directional filter topology is proposed where a transmission zero is introduced at no cost of increased total electrical length compared to classical topology. Two coupled line sections per wave-long resonator featuring unequal transmission lines are used for inter-resonator coupling. One of the sections is realized to be close to half-wavelength of electrical length at a center frequency so that its deep null is located at the edge of the filter`s stopband. The approach is theoretically analyzed and validated using a transmission line model of a 2nd order directional filter demonstrator operating at 1 GHz with 4% bandwidth. Simulation results confirmed the filter to exhibit frequency response with extra transmission zero certifying the usability of the proposed approach.

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The interest on higher frequency bands in satellite communications has never stopped increasing over the past years leading to the development of very high throughput satellite communication systems (VHTS) promising terabit per second capacity. This is only possible thanks to multibeam concepts, frequency reuse, polarization diversity and excellent maturity of semiconductor technologies that enable implementation of the most critical RF functions well beyond Ku-band. Hence, the scarcest resource, the bandwidth, becomes the only limit. Therefore, advanced HTS/VHTS feeder links can no longer rely on Ka-band. As a result, mm-wave frequency band as Q-band (33-50 GHz), V-band (50-75 GHz) and W-band (75-110 GHz) have gained in popularity as they can feed terabit streams between gateways and spacecrafts. These shorter wavelengths allow smaller antennas with higher gain as well as smaller chips and component sizes which reduces the overall weight of the payload. Systems are also less subject to interferences as the electromagnetic spectrum at mm-wave frequencies is less occupied compared Ka/Ku bands. First technology demonstrators and propagation campaigns have emerged even beyond Q/V band. W-band offering 2 x 5 GHz band between 71-76 and 81-86 GHz is considered as a natural next step to extend the capacity of the Q/V-band. To demonstrate the technology maturity and to enable preliminary propagation experiments, several W-band payloads have been developed and launched recently in the frame of projects cooperation like "W-Band Technology Developments towards first beacon-based propagation campaign'' that has been led by ESA. A W-Cube satellite with a 76 GHz beacon for propagation experiments has been in orbit since 2021 and another technology demonstrator that combines both W-band beacon and a high-throughput datalink EIVE is to be flown in 2023. This contribution will present development status of a W-band ground terminal capable of tracking beacon signals paced on LEO orbits. The system has been developed at ESA in the frame of YGT programs. The W-band terminal consists of a 60 cm two-reflector Cassegrain antenna used in terrestrial E-band radios. This antenna is equipped with a receive frontend based on a state-of-the-art LNAs processed on a 70 nm gate length GaAs mHEMT developed in dedicated ESA R&D activities. A custom made down-converter based on GaAs COTS is driven by a frequency-controlled PLL through SPI. Baseband processing is done with an SDR. The antenna together with the receive frontend are mounted on a low-cost antenna tracking system that has been adjusted to allow for fast LEO satellite tracking. System level aspects, design and measurements of the key elements as well as measurements results from field testing and overall system performances and limitations will be presented in this contribution.

It is theoretically investigated nonlinear propagation and interaction of two-dimensional and three-dimensional terahertz electromagnetic beams of different polarizations in nonlinear crystals. The attention is paid to crystalline paralelectrics like SrTiO3 at the temperatures 50 – 200 K. The interacting wave beams are subject to the modulation instability that results in the formation of the sequence of short envelope pulses of 2 - 10 picoseconds durations from the long input envelope pulses. The energy transfer from the pulse with the higher input amplitude to one with the smaller input amplitude occurs. The initial focusing of the beams compensates the wave losses and reduces the input amplitudes for observing the modulation instability.

This paper studies frequency-domain backscatter communication (BackCom) links. Specifically, we propose a new conjugate multiplication (CM) method that enables frequency-domain BackCom functional for dynamic digitally IQ-modulated ambient signals. Through both theoretical analysis and its millimeter Wave (mmWave) proof-of-concept experimental validation, its feasibility and performance superiority for different ambient signals, e.g., single-tone continuous wave (CW) and QPSK modulated signals of different bandwidth, are demonstrated and compared with the traditional frequency-shifted and recently proposed Quadrature Demod (QD) method.

This article presents a 26.5-29.5 GHz dual-polarized antenna array with electronic beamforming dedicated for 5G systems. Antennas are integrated with 16 beamformer ICs on multi-layer PCB. The array demonstrates a realised gain of 21 dB in operating bandwidth. Scanning ± 60° in both azimuth and elevation plane is achieved.

The recent advancements in terahertz (THz) physics drive the development of 6G technology. Multiplexing THz signals into a single optical path represents a highly promising technique for enhancing the data capacity of forthcoming data links. This study introduces the concept of applying two different diffractive elements to combine THz beams into a single communication channel, subsequently separating them for detection. These elements have been designed, optimized, simulated, manufactured, and experimentally validated.

This research project focuses on monitoring and recording specific vital signs, such as heart rate (HR) and breathing rate (BR), from human participants. Leveraging the capabilities of the INRAS GmbH Radarbook2, a 77-GHz multiple-input and multiple-output (MIMO) frequency-modulated continuous wave (FMCW) radar, we employ principal component analysis (PCA) on aggregated range-angle maps (RAM) that are spatially sliced. Through the analysis of multiple features extracted from slow-time samples of phase data, PCA effectively distinguishes between signal and noise, resulting in a more robust representation of the underlying vital signals. This study evaluates the performance of the proposed algorithm against the EQ02+ LifeMonitor, a cutting-edge wearable sensor employed for establishing ground truth values. Analysis of conducted experiments indicates a low mean absolute percentage error (MAPE) of 2% for HR and 3.3% for BR measurements.

Pollinators serve a crucial role in our global ecosystem by facilitating the reproduction of plants and crops. Despite their vital contribution, factors like urbanization and pesticide use, pose significant threats to the habitats of various pollinator species, such as bees. Therefore, it is increasingly imperative to devise solutions that allow precise and efficient monitoring of their biodiversity. This study presents a low-cost solution based on mmWave Doppler sensor to extract important characteristic wingbeat information of bumblebees through near-field monitoring. By conducting various simulated and real-life experiments, we demonstrate the feasibility of our approach for providing lowcost and effective portable in-field monitoring of pollinators for biodiversity conservation purposes.

This study bridges the evaluation of design parameters in breast microwave imaging (BMI) systems with innovative methodologies for assessing image quality. By comparing three distinct BMI system designs tailored for clinical, laboratory, and field settings and applying quantitative metrics to analyze image quality, this research identifies the influence of system design and reconstruction algorithms on diagnostic efficacy. The investigation into bed-based, bench-top, and portable systems, together with several reconstruction methods, unveils insights into optimizing breast cancer microwave imaging systems.

Multichannel RF Devices often suffer from problems with crosstalk between the channels. In this paper, an automated crosstalk reduction solution is presented. It was designed and used in a Cavity Simulator for European Spallation Source. First, the theory of operation is presented. In the next part, the used hardware is discussed. The software algorithm follows it. In the last part, the measurements of the system operation are presented.

In this paper, we addresses the emergence of autonomous and semi-autonomous radio frequency (RF) measurements as a vital application for robots, particularly in indoor environments where traditional methods are labor-intensive and error-prone. We propose a method utilizing Autonomous Mobile Robots (AMRs) equipped with Light Detection and Ranging (LiDAR) and RGB-D cameras to conduct precise and repetitive RF signal measurements autonomously. The system architecture, comprising both hardware and software components, enables seamless integration and operation, reducing human intervention to preparation and analysis tasks. The proposed solution demonstrates its efficacy through experimental validation, showcasing its capability to conduct autonomous measurements with high precision and efficiency, thereby enhancing the testing of wireless communication systems and algorithms.

Among many different space-based sensor technologies, Synthetic Aperture Radar (SAR) plays an essential role in providing timely and reliable geospatial information as it is the only sensor technology which provides high-resolution imagery on a global scale independent of the weather conditions and solar illumination. This talk will first provide an overview on the state of the art in spaceborne SAR. A prominent example is the TanDEM-X mission, the first bistatic radar in space consisting of two satellites in close formation flight. The second part of this talk describes the paradigm shift is taking place in spaceborne SAR systems. New antenna and SAR instrument concepts with multichannel and digital beamforming will boost the performance of future SAR systems by at least one order of magnitude. Augmenting complex SAR missions with global coverage, low-cost, lightweight SAR systems based on NewSpace concepts are being implemented with the aim of imaging small areas with a very short revisit time. The talk concludes with a vision for spaceborne SAR.

Passive radar has now become an established technology. Among current active field of research it is worth mentioning the capability to perform imaging as well as the capability of detection of small objects such as drones. Satellite Illuminators of Opportunity (IOs) such as Digital Video Broadcast - Satellite (DVB-S) as well as the exploitation of emerging broadband communication satellite constellations (e.g. Starlink or OneWeb) offer interesting characteristics to perform these two tasks. In fact, they offer relatively wide signal bandwidths for passive radars (up to 2 GHz), they operate at high carrier frequencies (namely in Ku-Band), and these so-called mega-constellations with global and continuous coverage are planned to be composed of hundreds or thousands of satellites deployed at low Earth orbits (LEO), thus offering continuous and synoptic illumination on wide and also remote areas. In particular, while the wide signal bandwidth enables high range resolutions, the high operating frequency significantly increases the system sensibility against Doppler (and micro-Doppler) modulations with respect to other conventional passive radar IOs at lower frequencies. Both these aspects offer extremely appealing characteristics for detection and imaging. Finally, preliminary experimental measurements will be presented. All of these analyses will provide an overview of the great potential capabilities achievable by using these novel satellite constellations as illuminators of opportunity, trying also to promote further research and developments in this field that will open up new and advanced passive radar applications.

Imaging radar could be a key component for high level autonomous driving. However, in electronic MIMO and phased array radar systems, the imaging capabilities are constrained by the small antenna aperture size. This limitation arises from the significant losses incurred by electronic links (typically a few dB/cm). In contrast, fiber optical links exhibit remarkably low loss, with values below 0.3 dB/km. Leveraging this advantage, radar systems with nearly infinite aperture sizes can be implemented. Within the talk, various photonic radar approaches are presented and discuss their applicability in automotive environments. Additionally, the talk will delve into the realm of photonic quantum radar. These approaches have the potential to overcome classic radar limitations, such as overcome the Rayleigh limit and achieving outstanding SNRs.

The low frequency performance of a combined edge-slot Vivaldi antenna suitable for ground penetrating radar is investigated. By implementing different exponential and edge slots in the conductor layer, the simulated gain and reflection coefficient parameters are improved compared to the conventional Vivaldi antenna. The modified antenna demonstrates wide impedance bandwith less than -10 dB with positive gain from 75 MHz to 1 GHz. A maximum gain above 7 dBi is realized in simulation. With its low frequency operation, gain improvement and low design profile, the proposed antenna makes a key candidate for low frequency GPR applications.

This paper investigates two different miniaturized horn antenna designs developed with the assumed high temperature resistance and impedance match. Apart from different geometries the developed antennas differ in impedance matching methods used for reflection coefficient improvement. It is shown that such designs can be realized at a cost of lower gain and higher sidelobe level. One of the designed antennas was manufactured with the use of substrate integrated waveguide (SIW) technology and the obtained measurement results are in a good agreements with simulations.

This article presents an electrically steerable parasitic array radiator (ESPAR) switched beam antenna with a dielectric overlay to miniaturize the antenna and modify the radiation pattern in the vertical plane. The antenna is intended for a gateway in a wireless sensor network (WSN) and is located on the ceiling of a room. Because the ESPAR antenna consists of an array of vertical monopoles, there is a deep minimum in the radiation pattern right beneath the antenna. The use of a dielectric overlay improves the radiation pattern in the vertical direction. Systematic tests in realistic indoor environment in the 2.4 GHz frequency band were conducted, which showed improved connectivity with wireless sensors placed near the floor in a wide area beneath the antenna.

In this article, we show how different infill patterns influence the overall performance of miniaturized electrically steerable parasitic array radiator (ESPAR) antenna. The use of 3D printed dielectric overlays is a simple and flexible way to miniaturize ESPAR antennas, so they are more compact and can be better integrated with wireless sensor network (WSN) nodes or gateways in different application areas. Additionally, such overlays modify antenna radiation patterns in elevation, which can be used to provide better connectivity with WSN nodes places beneath a WSN gateway. In this work, we investigate 3 different infill patterns that can be used in widely available 3D printers to create the overlay in a 3D printing process, and we show how each of the infill patterns used affects the antenna performance. Finally, based on our measurements, we propose the infill pattern that provides the best parameters of a miniaturized ESPAR antenna.

Most photoreceivers' frontends rely on an assembly of a photodiode (PD) and a transimpedance amplifier (TIA) to convert the received optical signal into an amplified electrical one. However, ensuring sufficient electro optical bandwidth, signal-to-noise ratio, and linearity for future Tb/s-class transmitters is challenging as the PD TIA interconnect becomes a significant issue. We report an optimization methodology of the frontend's Electro-Optical Response (EOR), in tuning the TIA's input impedance to eliminate the resonances originating from the interconnection. We also discuss the importance of the photodiode and PD-TIA interface modeling for the optimization. After optimization, the frontend achieves a 67-GHz Butterworth-like simulated electro-optical response, with 23 GHz of bandwidth control and clear 112-GBd PAM-4 eye opening. With the proposed optimization, the frontend demonstrates a high resilience to a +/-30% interconnection inductance variation.

In this work H2 optimal rational approximation of filter S-parameters is proposed. The method allows to introduce a restricted number of transmission zeros in the approximation process. It is shown that restriction for the number of transmission zeros is beneficial for improving the approximation results. Proposed method introduces restriction on McMillan degree for obtained rational representation, thus the results of approximation can be used directly for coupling matrix extraction. The method was verified by obtained excellent approximation results for measured S-parameters of a 10th order cross-coupled filter.

This study examines low-loss microwave propagation, which is achieved by creating scattering invariant mode (SIM) using antenna-beam forming, which is less affected by the statistical variation of the media than the regular beams used in radio wave communication techniques. The SIMs are calculated by measurement of the scattering structure in an anechoic chamber, using metallic cylinders as scatterers. Alternatively, for comparison, a hybrid method based on numerical calculations and the Foldy-Lax approximation is used to obtain fast results in the numerical analysis of the computationally large 3D problem. The robustness of the Scattering Invariant Modes is examined by varying the geometry of the model.

This paper presents a study on the effect of synchronisation errors in multi-receiver passive radar systems. In multi-receiver networks, the coherent detection assumes accurate synchronisation between the receivers, but practically this is difficult to achieve in practice. By creating a virtual radar environment we can investigate the effect of time offset, frequency offset and drift in different receiver configurations. Using the Generalised Canonical Correlation Analysis (GCCA) detector, the effect on performance is analysed under controlled conditions. The key output of this work involves an understanding of the required accuracy for distributed receivers which can help inform future work into multi-receiver passive radar and distributed beamforming systems.

Quantum mechanical phenomena are revolutionizing classical engineering fields such as signal processing or cryptography. When randomness plays an important role, like in cryptography where random bit sequences guarantee certain levels of security, quantum mechanical phenomena allow new ways of generating random bit sequences. Such sequences have a lot of applications in the communication sector and beyond. They can be generated deterministically (e.g. by using polynomials, resulting in pseudo-random sequences) or in a non-deterministic way (e.g. by using physical noise sources like external devices or sensors, resulting in random sequences). Important characteristics of such binary sequences can be modelled by gap processes in conjunction with the probability theory. Recently, all-optical approaches have attracted a lot of research interest. In this work, an adaptation of the quantum key distribution (QKD) setup is utilized for generating randomized bit sequences. The simulation results show that all-optically generated sequences very well resemble the theoretically ideal probability density characteristic. Furthermore, m-sequences show very promising results as well as Gold sequences. Additionally, the level of burstiness, i.e. the distribution of one's and zero's throughout the sequence, is studied for the different sequences. The results lead to the finding that generator polynomials with concentrated non-zero coefficients lead to more bursty bit sequences.

We present the procedure that allows one to establish the maximum time-step size guaranteeing stable finite-difference time-domain (FDTD) simulations in media described by time-fractional constitutive relations. The considered constitutive relations involve fractional-order (FO) derivatives based on the Grunwald-Letnikov definition, which describe hereditary properties and memory effects of media and processes. Therefore, the current values of the electromagnetic field in the FDTD iterative procedure depend on all previous ones, which is a new type of computational scheme for this method. In this contribution, we focus on the derivation of a new stability condition for such an FDTD scheme. We formulate fundamental equations of the proposed FDTD method and, then, we derive the stability condition. In the next step, we analyse the properties of this condition on the complex plane based on the characteristic equation of the method. Our results are useful for researchers investigating numerical techniques modelling electromagnetic processes described by the diffusion-wave equation and FO derivatives.

Real-world antenna design typically relies on empirical methods, where the development starts with structure synthesis followed by its iterative adjustments to achieve the desired performance. Although the outlined approach proved to be successful, it is also dependent on engineering experience. Alternatively, development can be performed automatically based on the specifications. In this work, an unsupervised design of topologically agnostic patch antennas is considered. The method involves a random generation of feasible topologies, followed by classification of the designs and their cost-efficient numerical optimization. The outlined framework has been used to determine two sets of geometrically distinct radiators dedicated to work for the frequency ranges of 5.3-5.9 GHz and 7-8 GHz, respectively. The generated antennas have been compared in terms of the electrical and radiation performances. The results indicate that the use of free-form topologies has a notable effect on the performance of antennas developed to operate in the given frequency spectrum.

In this paper, a practical approach to the design of selected microwave circuits with Non-Uniform Transmission Lines (NUTLs) is presented. Influence of NUTL shape and dielectric constant of a substrate on the frequency response of a line is investigated and described. To prove the NUTL's usefulness, a branch-line coupler (BLC) with 3rd harmonic suppression and broadband output matching network of a power amplifier is designed and compared with their conventional counterparts, composed of only uniform transmission lines.

Additive manufacturing technology provides high flexibility in designing custom enclosures for prototype devices such as nodes of distributed sensor networks. Although integration of components is desired from the perspective of sensor mobility, it might negatively affect the performance of radio-connectivity due to couplings between the antenna and system peripherals, as well as other unaccounted effects of the 3D printed enclosure. In this work, a design of a dual-band cellular antenna is considered. The structure is optimized to work on plastic substrates characterized by thicknesses ranging from 1 mm to 5 mm, respectively. The antenna features a –10 dB bandwidth within frequencies from 0.74 GHz to 1.05 GHz and 1.49 GHz to 1.92 GHz. Owing to a simple topology the structure can be implemented in the form of a copper-based sticker and attached on a 3D printed material (e.g., the enclosure of the device). The radiator has been compared against the state-of-the-art antennas in terms of bandwidth and gain.

In this article, we present a numerical method to determine the EM susceptibility pattern of shielded object with apertures. This method uses surface integral equations in combination with the method of moments and the computational domain decomposition technique (SIE-MoM-DD) to model the object and electric field in its interior.

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Ship size estimation is important for ship classification. In this paper a novel and fast ship size and heading angle estimation method for focused synthetic aperture radar (SAR) and ISAR (inverse SAR) images is proposed. The eigen information of the detected ship pixel positions are used for estimating the size and heading angle of the ship. The proposed method is compared with several state-of-the-art algorithms. Real spaceborne radar datasets are used for evaluation.

Forming synthetic aperture radar images in real-time using the backprojection algorithm (BPA) requires optimal use of available hardware. We discuss the challenges and feasibility of implementing the BPA to achieve good performance on graphics processor units (GPU) platforms. We will compare the achieved performances between high-end GPUs, CPUs (x86-64 and ARM) as well as edge devices with low-performance GPUs. Benchmark results prove the feasibility of real-time processing with embedded GPUs using less than 40 Watts of power.

This work introduces a system-level model for radar signal generation, developed to support the latest applications of radar technology like automotive radar industry, high-resolution RF security screening and vital sign monitoring. This study models the dynamic environmental geometry sourced from conventional 3D software such as Blender. Subsequently, it introduces a ray tracing approach incorporating multipath reflections and line of sight based ray allocation to accurately compute the delay and amplitude of received signals based on the radar equation. The proposed model supports a range of conventional multichannel FMCW radar techniques, including phased array, slow time TDM, BPM, DDM MIMO radar for the generation of received signals. The simulation results from the CUDA GPU-accelerated implementation demonstrate the capabilities of the proposed radar signal simulator.

TOPSAR has operational advantages over conventional synthetic aperture radars (SARs) by steering the beam in the azimuth direction. However, because of its complex observation geometry, azimuth resolutional degradation occurs when the illumination mode is highly-squinted. In the highly-squinted TOPSAR (HS-TOPSAR), symmetrically located targets along the flight trajectory have almost the same Doppler history, resulting in ambiguities, whereas beam steering narrows and skews the received spectrum, reducing signal orthogonality and introducing spectral folding. As a result, the Doppler gradient becomes too small to be precisely measured, limiting fine azimuth angular resolution, and causing azimuth ambiguities when reconstructing the image. To this end, an extended hybrid-domain IFA based on azimuth iterative focusing is proposed to overcome such azimuth-variant characteristics. The simulation results and metrics demonstrate the applicability of the IFA.

The talk will introduce the aspects and challenges of Electromagnetic Warfare (EW) in the context of modern electromagnetic spectrum operations. Dominating the electromagnetic spectrum is a critical task in all military conflicts, enabling to detect enemy forces, to deceive them or to disrupt their efforts. Radar threats evolving from static to agile, from adaptive to cognitive waveforms, from single site to distributed and netted systems increasingly present prior unknown actors. New approaches to intercept, analyse and characterize those signals are based on machine learning techniques to cope with responsive and unpredictable behaviour in the EW environment.
The spectrum usage can be weakened or even disabled by sophisticated applica-tion of Electromagnetic Attack (EA) as one of the three EW pillars. An on the fly decision or design of suitable, responsive EA techniques against identified, agile threats without relying on pre-programmed libraries is crucial to stay ahead of the threat's capabilities in the future. Finally, an assessment of the countermeasures' effectiveness is required to close the loop to Cognitive EW, learning during the mission, improving EA techniques and self-protection capabilities.

The talk will be Unclassified

The paper examines the edge detection methods for radar recognition using convolutional neural networks. A short analysis of selected edge detection methods was made. The results of research comparing the edge detection methods and verification their usefulness in radar recognition process are presented. Based on the available neural networks AlexNet, GoogLeNet and Darknet-53 in the MATLAB environment, the radars were recognized based on their antennas images. The results of correct radar recognition are depicted in the appropriate figures.

Rural clutter channels, which vary over time, significantly impact radar measurements and communications, but predicting their amplitude, Doppler, and phase characteristics remains a formidable challenge. This study endeavors to incorporate the effects of rural bistatic radar channels into simulations by analyzing transfer functions derived from real X-band measurement data. We introduce a denoising diffusion probabilistic model aimed at capturing the intricate characteristics of fast-fading channels, thus facilitating the augmentation of the dataset of measured clutter channels for more robust modeling. This work is based on previous research in generating clutter signal data using generative adversarial networks [1]. Potential usage of the proposed model is testing and evaluation of radar systems by providing realistic simulations of rural clutter channels.

Due to the rapid development of cognitive electronic warfare (CEW) and complex electromagnetic environments, traditional jamming methods are difficult to adapt to new types of scenarios. Reinforcement learning (RL), as one of the cores of machine learning, provides a solution for jammers to adapt to new challenges. In order to quickly find a jamming policy for multifunctional radar (MFR), this paper proposes a jamming policy generation scheme based on the Advantage Actor Critic (A2C) algorithm, which utilizes interactive self-learning to dynamically adjust the jamming policy and realize cognitive jamming decision generation. Firstly, this paper investigates the model of jamming policy generation and discusses the relationship between radar operating modes and jamming modes, and the whole process can be modeled as a Markov decision process (MDP). In this paper, a heuristic reward function is used, which helps the jammer to better explore the optimal strategy. Secondly, we discuss the A2C algorithm, especially the advantages of this algorithm over other RL methods for which research results are available. Finally, in this paper, we compare the simulation results of the A2C algorithm with Q-Learning and DQN algorithms, and demonstrate that the algorithm effectively improves the cognitive jamming policy generation ability of the jammer.

Narrowband interference causes false detection of the target when interference CS (Chirp sequence) radar has the same chirp rate as the measurement CS radar. Narrowband interference theoretically appears as line spectrum, however experimental results show that its spectrum is spread in ranging spectrum and its frequency changes according to time. This paper describes measurement and analysis of narrowband interference and shows how hardware imperfections cause frequency shift and spectrum spreading of narrowband interference. Furthermore, it discusses impact on narrowband interference suppression and proposes block-wise noise level estimation to improve narrowband interference suppression performance.

This paper introduces a radar-density based simulation tool to investigate mutual interference in automotive frequency modulated continuous waveform (FMCW) radars. Employing simulation, the average increase in the noise floor caused by interference across various radar densities is analyzed. Moreover, the impact of interference on two distinct radar application scenarios is assessed. The proposed methodology serves as a valuable tool for comprehensively evaluating the performance of FMCW radars under interference conditions and testing the efficacy of interference mitigation algorithms.

Mutual interference between radars is one of the major obstacles currently faced by automotive industry towards the attainment of full vehicle autonomy. This paper presents an analysis and mitigation of interference in the spatial domain and evaluates its efficiency compared to the traditional mitigation techniques for various road scenarios and radar configurations. The performance metrics, including peak-to-highest side lobe levels and signal to interference plus noise ratio, have been assessed based on the angular separations between the target and interferers to highlight the cases where spatial domain mitigation might be suited.

This work confronts the complex issue of cross-interference in Frequency Modulated Continuous Wave (FMCW) radars, a critical concern that has become more pronounced with the proliferation of automotive radar systems. The study introduces a two-dimensional autoregressive (AR) modeling technique for signal reconstruction in the time domain, tailored specifically for the textured nature of FMCW radar frames composed of fast-time (Range bin) and slow-time (Doppler bin) signals. According to the simulations conducted in this study, the proposed 2-D AR model (of order 3) exhibits superior performance compared to its 1-D counterpart (of order 5). This is evidenced by a slightly lower Mean Absolute Percentage Error (MAPE) during model training and a higher Signal-to-Interference-plus-Noise Ratio (SINR) for the reconstructed signal, suggesting that the 2-D model requires less frequent temporal sampling. The study further investigates different sampling strategies and evaluates the influence of model order on signal reconstruction. Based on these assessments, a third-order 2-D AR is recommended as a suitable trade-off model for interference mitigation of FMCW radars for the evaluated scenarios. This paper is structured as follows: Section I defines the interference problem in FMCW radars and the latest solutions to this problem are discussed. Sections II and III include the working principles of FMCW radar and theoretical backgrounds about multi-dimension auto-regressive modeling, respectively. Eventually, the mitigation techniques and numerical evaluations of the proposed approach are presented in Sections IV and V.

In this work, a Doherty amplifier (DA) implemented in an InP DHBT technology is investigated for enhanced power-added-efficiency (PAE) and 6-dB power-back-off (PBO) efficiency in D-Band. The DA is implemented with standard common-emitter power cells, as well as power cells with enhanced gain. The gain enhancement is achieved by adding driver stages or by implementing power cells in stacked topology. The best achieved simulated performance of a DA circuit implemented using a Class-AB main amplifier and Class-C auxiliary amplifier demonstrates a gain of 3.5 dB, peak PAE of 29.4%, and 6-dB PBO efficiency of 11.1%, at 140 GHz. In comparison, a simulated performance of a single-stage common-emitter Class-AB power amplifier demonstrates a gain of 5.1 dB, peak PAE of 33.1%, and 6-dB PBO efficiency of 14.8%, showing no advantage of using DA for high dynamic range signal amplification in D-Band.

The paper presents the results of experimental studies illustrating the influence of the assembly quality of RF transistors on their thermal resistance. The measure of assembly quality is the total voids in the solder joint. The influence of the location of the tested transistors on the printed circuit board on the value of thermal resistance was considered. The non-uniformity of temperature distribution on the surface of the tested transistors was also analyzed. The impact of the obtained research results on the lifetime of the considered transistors was discussed.

A broadband, fully integrated 4-channel Multiport Amplifier (MPA) operating at 1 GHz center frequency has been presented in this paper. Designed MPA consists of two 4 x 4 Butler matrices and amplifying blocks based on ADL5611 amplifiers offered by Analog Devices. To obtain broad operational bandwidth, Butler matrices are composed of coupled-line sections. Moreover, the circuitry has been designed in the microstrip technique to simplify the integration of passive and active parts of the multiport amplifier. The described circuit has been proven theoretically with circuit simulation, then designed, simulated electromagnetically, and manufactured.

This study presents the introduction of a Class- F amplifier operating at X-band, employing a GaN HEMT. Alumina thin film substrate was utilized in the design of matching networks. The final configuration of the amplifier is housed in a metal enclosure with connectors, forming a hybrid structure that incorporates a bare die GaN HEMT, bonding wires, and thin-film-based input and output networks. The design process considered the impact of the transistor's intrinsic parasitics and the effects of bonding wires to ensure Class-F waveforms at the output. The measurement results demonstrate an output power of 39.8 dBm, 57.4 % power-added efficiency (PAE), and a gain of 13.9 dB at a frequency of 7.76 GHz.

Microstrip three-way (that is, 4.8 dB) integrated filtering power divider (FPD) is presented in this paper. The proposed FPD evenly distributes an input power signal into three equal output signals. The design incorporates balanced signal power division, and filtering technology for the removal of unwanted frequency elements and aimed at enhancing signal quality and efficiency in the radiofrequency (RF) front-end of communication systems. Microstrip folded-arms square open-loop resonator (FASOLR) is employed in the design implementation to achieve compact size. The proposed FPD features a 2.6 GHz centre frequency, with a 0.03 fractional bandwidth. The implementation is carried out on Rogers RT/Duroid 6010LM substrate with a dielectric constant of 10.7, a thickness of 1.27 mm and a loss tangent of 0.0023. The good agreement between the theoretical and practical results verifies the effectiveness of the FPD in delivering equal power outputs at the three output ports, and at the same time filtering out unwanted frequencies. The practical results of the prototype FPD indicate a good return loss of better than 15.5 dB and an insertion loss of better than 4.77+0.34 dB. The design prototype achieved compact size of 0.31 λg x 0.18 λg. λg is the guided wavelength for the microstrip line impedance at the centre frequency of the 3-way equal filtering power divider.

This paper introduces a pioneering approach to the design of an ultra-wideband (UWB) microstrip bandpass filter featuring a narrow notch. The proposed filter incorporates two identical high-impedance short-circuited stubs, one low-impedance short-circuited stub, and two identical sections with three parallel-coupled lines. The electrical length of both the short-circuited stubs and the parallel-coupled lines is meticulously set to a quarter-wavelength at the center frequency of the desired passband. Additionally, a very short-length open-circuited stub is strategically placed at the end of one of the outer lines in a parallel-coupled line section. This configuration enables the filter to exhibit a narrow notched band within the passband, effectively attenuating unwanted WLAN signals. The filter is designed utilizing a microstrip substrate characterized by a relative dielectric constant of 10.8 and a thickness of 1.27 mm. The design of the proposed filter is successfully realized in theory and verified by full-wave electromagnetic simulation and the experiment. An excellent agreement between the expected and measured results is obtained.

The recent proliferation of personal wireless communication devices is driving the need for multi-band frequency selective components including multiplexers and dual-band filters. This paper presents a simple technique for transforming a single-band bandpass filter (BPF) into a dual-band BPF. A second order (two-pole) single-band bandpass filter was chosen for this research, giving rise to a fourth order (four-pole) dual-band bandpass filter after the proposed filter transformation. Both filters were then implemented using the compact U-shaped microstrip resonator for improved device miniaturization. The proposed work features a centre frequency of 1.4 GHz for the single-band bandpass filter, with a span of 3.4% fractional bandwidth. The dual-band bandpass filter operates at 1.35 and 1.45 GHz. The design implementation employs the commercially available Rogers RT/Duroid 6010LM substrate, having a dissipation factor (tan δ) of 0.0023, dielectric constant (εr) of 10.7, diel thickness (h) of 1.27 mm, and top/bottom cladding of 35 microns. The results reported for the theoretical and practical designs show good agreement and improved performance when compared to similar research works in literature. The practical responses of the prototype dual-band BPF indicate a good return loss of better than 18 dB across both bands, and an insertion loss of better than 0.1 dB. The design prototype achieved physical size of 0.23 λg x 0.18 λg. The results reinforce the design's competitive edge in performance. λg is the guided wavelength for the microstrip line impedance at the centre frequency of the filter.

� Abstract � In this paper, the design of a novel 4 x 4 Butler Matrix composed of broadband branch-line couplers has been presented. To enhance the operational bandwidth of the circuit, for the first time, a branch-line coupler having additional two-section impedance transformers introduced in [16] has been utilized. To verify the applicability of the proposed design, two Butler matrices have been designed: in PCB and MMIC technologies. PCB circuit operates at 2 GHz center frequency. The structure has been designed, fabricated, and measured. The MMIC version of the considered Butler Matrix has been designed in the PH10 GaAs process offered by UMS and operates at 26 GHz center frequency. The circuit has been only designed and simulated electromagnetically.

By axially loading of a cylindrical wire we utilize the first order buckling mode to form the shape of a segment of a wire loop inductor. The shape of the deformed wire is expressed in analytical form and provides the basis for a semi-empirical formulation of the loop inductance. Combining several buckling segments and taking advantage of the snap-through behavior of such a segment, the shape of the wire loop in air and hence the loop inductance can be varied mechanically on purpose. The analytical model for the tunable inductance enables a design methodology for bistable compliant inductors. We present two designs of mechanically tuned inductors in the range from 20 nH to 50 nH. Furthermore the electromagnetic properties of the proposed innovative components are confirmed by method of moments numerical modeling based on quasi-static magnetic fields and by experiment. We finally show that the design process is applicable to regular plane polygonal inductors representing multi-stable compliant stages.

In this study, an X-band low noise amplifier (LNA) that achieves less than 0.7 dB noise at 7.75-8.5 GHz is designed and fabricated for X-band satellite communications. Four-stage amplifier using both MMIC amplifiers and transistors. LNA is designed for 50 dB gain. Consequently, the X-band of the suggested design is far less noisy than that of its commercial equivalents.

The European Spallation Source in Lund, Sweden, is planned to be the world's most powerful pulsed neutron source. The machine includes a 600 m long proton accelerator with almost 300 RF resonator cavity structures and beam diagnostic devices, a five-ton tungsten target wheel, and fifteen instruments for science known as experimental stations. An essential requirement for ESS is to ensure a precise phase synchronization of the subsystems. The phase accuracy requirements are 0.1o for the short term, 0.1o for the long term between adjacent outputs, and 2.0o for the long term between any two outputs. This paper covers the design and installation of the active phase drift compensation system in RF connection from the Master Oscillator to the Phase Reference Line for the European Spallation Source. The system stabilizes phase simultaneously at 352.21 MHz and 704.42 MHz reference frequencies. It also demonstrates simultaneous group delay drift reduction from 18.1 ps to 0.71 and 0.87 ps at 352 MHz and 704 MHz, respectively, without noticeable degradation of the residual phase noise. The drift suppression factor equals about 20 and is considered an excellent result, considering the system's complexity and the necessity of measuring phase at a distant cable end. The system was implemented in the ESS facility and has been successfully operated there since 2021. Further tests are planned in 2024.

A new version of a coaxial loop-coupled Fabry-Pérot open resonator (FPOR) with a significantly enhanced Q-factor is reported. Measurements have been performed in the 40 GHz - 130 GHz range. The resonator is coupled using a 0.6 mm diameter coaxial line located at the center of each mirror. Compared to an FPOR coupled with a 1.0 mm diameter coaxial line, the Q-factor increase is up to 10-fold.

The paper presents a computer simulation software aimed at assessing the multipactor threshold power in a rectangular waveguide working with single tone excitation. Initial tests demonstrate a strong agreement between the simulation results obtained and those from commercial software. Contrary to the existing commercial software, our tool will be provided as Open Platform, for free use and popularisation of knowledge about physical phenomena resulting from interactions of microwaves with materials.

This study uses density functional theory (DFT) to investigate the electromagnetic (EM) properties of silicon carbide (SiC), specifically focusing on cubic type 3C. Using the SIESTA program, the crystal structure of SiC is modeled. In the simulations, the influence of the electric field in two directions is considered, demonstrating the anisotropic behavior of the material. From the real and imaginary permittivity, the loss tangent in SiC up to 450 THz was calculated with the smallest value for 72.5 GHz. Conductivity is also obtained for this particular frequency.

3D-printed materials made of a liquid photocurable resin using a gyroid latticing technology are characterized in the frequency range spanning from 1.9 up to 110 GHz using split-post dielectric resonators and a Fabry-Perot open resonator. It is shown that such materials can be low-loss in a broad frequency range if appropriate settings of the lattice are employed. Presented measurements confirm theoretical predictions that such lattice structures exhibit an upper cut-off frequency due to a lateral mode occurring in the structure, which mainly depends on the unit cell size. Another novel experimental finding is that the investigated materials exhibit in-plane anisotropy, typical for inhomogeneous structures. The proposed measurement methods provides a unique insight into electromagnetic properties of such 3D-printed materials, thus, enabling their further optimisation for the use at even higher frequencies.

Complex permittivity maps obtained by Split Post Dielectric Resonator (SPDR) material measurement technique yield limited resolution due to the weighted averaging over the region interacting with DR field. The motivation of this work is to improve spatial resolution for examining inhomogeneous samples and smaller homogeneous samples that do not meet the resonator's minimum size requirements. To achieve this, attempts were made to reverse the averaging. The electric field pattern is known from finite-difference time-domain (FDTD) simulation, and on this basis, an inverse problem is formulated. Due to the presence of additive noise in the measurements, matrix regularization techniques are investigated, such as Truncated Singular Value Decomposition (TSVD) and Tikhonov regularization, alongside established image restoration methods for noise-prone deblurring, such as Richardson-Lucy deconvolution, Wiener filter and Plug-and-Play Alternating Direction method of multiplier (ADMM).

This paper discusses the application of particular artificial intelligence methods in the process of extracting the permittivity of thin, dielectric materials using Fabry-Perot open resonator (FPOR). The main point of the measurements is presented. Then, the details of the measurement process are explained with highlighting the possible fields of improvement. Several chosen artificial intelligence architectures are shown, including classic normal networks, multilayer perceptrons and radial-basis networks. For the comparison, there have been also presented Mamdani and Sugeno fuzzy inference systems. There is described the procedure of the measurement, gathering data process and finally the performance is described on the example of medical materials.

3D printed polarisers for the terahertz (THz) frequency range have been investigated in this paper. The fused deposition modelling (FDM) technology allows cost-effective access to passive optical elements, especially for the sub-THz radiation range. In addition, it enables the use of different element base materials and customization. The performance of polarisers has been simulated, and the manufactured elements have been tested in different angular positions for a given frequency and a wide range of frequencies for the selected angles. The obtained results allowed for forming constructive conclusions about the material and fill factor of the polarisers that should be used.

Joint Communication and Sensing (JCAS) has garnered considerable interest, offering dynamic resource allocation and operational adjustments based on real-time inputs, optimizing energy efficiency and overall system performance. JCAS comes with its challenges. Despite sharing a common front-end in a JCAS transceiver, communication and radio sensing exhibit distinct specifications, primarily in bandwidth and linearity. For the RF front-end to effectively function in both radar and communication modes, it is essential to incorporate reconfigurability concerning parameters such as gain, linearity, frequency, and bandwidth. Illustrating the operation of two LNAs in the 5G and 6G bands, this paper investigates silicon-on-insulator (SOI) technology as a candidate for JCAS systems integration while highlighting the utilization of the back-gate bias feature to enhance reconfigurability in communication and radar system.

Synthetic aperture radar (SAR) payload generates enormous amounts of data that is dependent on the imaging bandwidth, now reaching up to 1200 MHz, as well as on the duration of each image and the ever increasing number of collections per orbit. All these factors combined with a requirement for fast data availability on ground necessitate a robust, adaptable downlink system with high throughput and reliability.

In our presentation, we will demonstrate how we tackled these challenges by leveraging the modular design of our satellites and the team's readiness to adopt new technologies. Specifically, we developed an X-band radio transmitter, which maximizes the utilization of available RF spectrum to address these requirements effectively.

Understanding the scattering physics of specific objects is important for their design and use. Imaging techniques may give this insight, provided that they can distinguish different scattering mechanisms. The use of compressive sensing (CS) in imaging allows to use different scattering models. In this paper, two models for surface wave (SW) scattering are described and applied to a canonical test case. We find that CS is effective in extracting the reflection of surface waves from the total radar echo. However, the standard L1-regularization of the CS optimization problem requires careful balancing of the different scattering models. It is shown that the Bayesian approach to solve the CS optimization problem does not suffer from this problem.

This paper presents an antenna system for a passive radar designed to operate in the DVB-T band covering frequencies from 450 MHz to 1 GHz. A setup of 8 Vivaldi antennas with reduced dimensions was developed for this purpose. The use of corrugation allowed to reduce the size of a single radiator, and consequently the entire antenna array. The results of computer simulations of the parameters of the developed antenna show its good impedance matching in the assumed frequency range as well as the directional radiation pattern of individual radiators.

In this paper design of a slotted waveguide array antenna with extended scan area is presented. Eigenmode solver of CST Studio Suite is used to determine the dispersion characteristics of waveguide structures and expected scan area. The designed slotted array operates in C-band with 8% bandwidth and has scanning area of approximately 30 degrees. Array characteristics are calculated using CST Studio full-wave electromagnetic software.

An Active Electrically Scanned Array (AESA) consists of numerous antenna elements where each of them has its own receiving channel until analogue-digital conversion. In this paper, an analogue microwave matrix called overlap beamformer (OBF) for 1D AESA is presented. OBF has the ability to reduce the number of receivers with a factor of 2 and without degradation of formed digital beams in desired operational sector. The proposed OBF exhibits ±10° scan sector and is designed in well-established microstrip PCB technology.

This paper investigates the usability of 4x4 Butler matrices for 16-QAM modulation and demodulation. The presented theoretical analysis shows that an appropriate choice of demodulator matrix input ports not only allows for using of non-matched power detectors without causing performance degradation, but also significantly reduces design complexity. The measurements of the manufactured circuits yield excellent electrical parameters and a good resemblance between the obtained and ideal constellation, confirming the efficacy of Butler matrices as 16-QAM modulators and demodulators.

The European Spallation Source (ESS) in Lund, Sweden, is based on a 600 m long linear proton accelerator (LINAC) with over 155 RF resonator structures, both normal and superconducting, operating respectively at frequencies of 352 MHz and 704 MHz. The accelerator will also be equipped with more than 150 various proton Beam Diagnostic (BD) devices. This paper covers the design and installation of the RF synchronization system in the ESS accelerator tunnel to provide phase reference signals for over 300 RF accelerator subsystems with accuracy reaching 0.1° at both operating frequencies. The described system consists of a Phase Reference Line (PRL), an entirely passive system based on a single 1-5/8" coaxial rigid line installed at the tunnel ceiling and supporting systems such as power amplifiers and temperature and gas pressure control systems. The 580 m long PRL was designed to distribute both reference frequencies from a Master Oscillator to 56 tap points in the tunnel. Each tap point contains a broad-band, adjustable directional coupler, passive diplexer, and a configurable set of power splitters to feed 3 or 6 signal outputs with equalized power levels. The entire PRL is temperature stabilized (+/-0.1 deg C) and includes an inner-line gas pressure stabilization to assure phase synchronization precision. This contribution covers the concept of the PRL, technical assumptions, the design, the installations, and current performance test results.

In this paper, permanent joints are investigated for assembly of the recently introduced Printed Circuit Board (PCB) integrated air-filled waveguide (AF-WG). The joints provide low-resistance contact between the metal-coated 3D-printed U-shaped waveguide shell and the on-PCB ground plane that serves as one of the guide walls. The above is an alternative to the originally proposed through-hole screw joint and studied snap-fit joints, which are a better choice at higher frequencies. Joints employing conductive glue and low-temperature solder were assessed by measurement of test vehicles being a long WR-42 sized waveguide section in-between two through-patch microstrip to AF-WG transition operating within 18 GHz to 26.5 GHz bandwidth. The obtained results show that solder joints might be attractive in terms of minimizing power losses, however, special care must be taken during the assembly process.

A dielectric disk resonator employing whispering gallery modes is one of promising sensors for millimeter-wave and sub-terahertz frequency bands due to its small size, high quality factor and ability to operate with one-side access to the object under investigation. However, the whispering-gallery-mode resonator operating on the fundamental mode is not well suited for testing bulky dielectric materials. The reason is that the resonance is crucially suppressed by stray fields arising in the tested material near the disk edge, and thus the high quality factor of the resonator cannot be realized. In this work, it is shown that the higher-order whispering gallery modes are preferable in such applications. Though the unloaded quality factor of the resonator sensor is not as high as in the case of the fundamental mode, it nevertheless suffices to detect small levels of moisture content in the dielectric materials. A dielectric disk resonator with the diameter of 20 mm and thickness 3 mm made of a high-purity alumina was used as a moisture sensor operating in the frequency band near 63 GHz. The performance of the dielectric disk resonator sensors was demonstrated experimentally in the evaluation of moisture content in thick sheets of ABS plastic and gasoline-water mixtures, when the water fraction in the material amounted to 200-1000 ppm.

PLA (Polylactic Acid) is commonly used for many standard 3D printers, as it does not require a special heated bed or heated chamber. This study presents several methods based on the transmission/reflection (TR) method to measure the permeability and permittivity of a 3D-printed PLA sample. Differently from the traditional TR methods by establishing scattering equations to determine permeability and permittivity of a material, in the new method, the longitudinal phase constant and the TE({10}) wave impedance are determined from S-parameters of the overall measurement before, then the electromagnetic material properties permittivity and permeability can be calculated using the formula of the TE({10}) wave impedance.

Method of Moments (MoM) is one of the most useful approaches for Radar Cross-Section (RCS) simulation, allowing i.e. the computation of the scattering from 3D models of real objects. However, it is limited by computer memory and computation time. In this paper, the authors explore the question of the balance between the possible acceptable level of 3D model simplification and the time benefit associated with a decrease in computational overhead due to the reduction of the model geometry complexity. A volume-based spatial RCS characteristics quality index is proposed. The authors present the results of the calculations performed for perfectly conducted sphere 3D models with varying levels of geometry simplification for which a simple analytical solution exists. Furthermore, the results of the computations performed for a generic missile model set are shown.

This paper is a brief description of the results presented in 10.1109/ACCESS.2023.3292961. and concerns an algorithm for finding the roots and poles of a complex function depending on two arguments (one complex and one real) is proposed. Such problems are common in many fields of science for instance in electromagnetism, acoustics, stability analyses, spectroscopy, optics, and elementary particle physics. The proposed technique belongs to the class of global algorithms, gives a full picture of solutions in a fixed region, and can be very useful for preliminary analysis of the problem. The roots and poles are represented as curves in this domain. It is an efficient alternative not only to the complex plane zero search algorithms (which require multiple calls for different values of an additional real parameter) but also to tracking algorithms. The developed technique is based on the generalized Cauchy Argument Principle and Delaunay triangulation in three-dimensional space. The usefulness and effectiveness of the method are demonstrated in several examples concerning the analysis of guides (Anti-Resonant Reflecting Acoustic Waveguide, coaxially loaded cylindrical waveguide, graphene transmission line) and a resonant structure (Fabry-Pérot open resonator).

In this paper we present a deep learning based approach for detecting changes or deviations in the context of radar based occupancy grid maps. Specifically, we propose a convolutional neural network (CNN) based architecture to identify spatial changes. As a reference map of the environment, we use occupancy maps generated using detections obtained from automotive radar sensors fitted to the corners of a test-vehicle. For the purpose of similarity learning, a siamese architecture is used. The network is trained with occupancy maps of highway and urban scenes captured over a period of time around the city of Wuppertal, Germany, focusing on construction zones on the road. As per the initial evaluations, the siamese network is able to classify images with construction zones as changes from non-changes i.e. images without construction zones.

This paper presents an innovative system concept for automotive radar antenna arrays, employing dual frequency bands to power two separate antenna systems from a common monolithic microwave integrated circuit (MMIC) port. This configuration enables the creation of both dense and sparse arrays or two distinct sets of arrays, enhancing angular accuracy and reducing computational complexity. The dense array disambiguate measurements of the sparse array, providing a larger aperture, while two sparse arrays offer increased accuracy. The system offers both ambiguous and unambiguous measurements capability for determining angle-of-arrival (AoA) of targets, promising significant improvement in angular accuracy with fewer receive channels.

We describe a dynamically adjustable diffractive element built to control GHz-THz radiation what makes it attractive for automotive radar applications. The device is based on nematic liquid crystals and interdigitated electrode design procuring a versatile reconfiguration capability with low losses. Among others, our approach allows the dynamic asymmetric energy redistribution (steering). Corresponding applied and fundamental aspects of the design are discussed also.

The Doppler shift in a combined light detection and ranging (lidar) and photonic radio detection and ranging (radar) sensor systems for large aperture phased array and multiple input multiple output (MIMO) is investigated. Reusing the optical frequency modulated continuos wave (FMCW) local oscillator (LO) signal of a photonic radar system could be beneficial for coherent large aperture phased array MIMO lidar systems with almost no additional cost. Within this paper, the Doppler shift of such a lidar radar combined sensor (LiRaS) system is analysed. It should be noted, that all components of a LiRaS system can be monolithically integrated into silicon based electronic photonic integrated circuits (EPICs).

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In this paper, we present important challenges in modern optical networks generated by a skyrocketing traffic demand growth. We present the recent evolutions in hardware and software used for optical transmission. Semiconductor technologies for high-speed ICs and examples of circuit design and realizations are discussed. Finally, we present the key and recent system experiments for new generations transceiver developments.

Over-the-Horizon Radar (OTHR) uses high frequency (HF) radio wave propagation to detect targets up to thousands of kilometers away through ionospheric refraction and reflection. However, OTHR operation at high latitudes is impeded by irregular and variable enhancements to the electron density from precipitation in the auroral region, increasing the ionospheric absorption of HF radio waves and reducing the usable frequency range. A precipitation enhanced E-layer model was developed for the Empirical Canadian High Arctic Ionospheric Model (E-CHAIM) to improve upon the electron density profile at lower altitudes. In this paper, the monthly median absorption is modeled for feasible operating frequency and elevation angle radar parameters to assess the effect of ionospheric absorption on OTHR in Canada.

The Radar Cross Section (RCS) of commercial micro and mini drones was characterized with a Commercial-Of-The-Shelf (COTS) Radar, using Frequency Modulated Continuous Wave (FMCW) waveforms, operating at 24 GHz. This paper presents a synthesis of measurements and some statistical inferences aimed to verify the correspondence of experimental densities with those ones of theoretical models.

Coded aperture imaging based on a metamaterial array antenna (MCAI) is a promising technology for high-resolution forward-looking radar imaging. However, existing methods for building imaging models always assume that the reflected signal from each metamaterial phase modulation unit has the same transmission amplitude, which introduces significant amplitude errors in practical MCAI scenarios. In this paper, a pathloss-based amplitude model is proposed for MCAI. The impact of the transmission distance and the antenna's directivity on the transmission amplitude is formulated as loss factors. The refined model provides a more accurate estimate of the amplitude model for MCAI with the metamaterial phase modulation unit. Subsequently, a simplified pathloss model is utilized in a radiation pattern measurement experiment to verify the effectiveness of the proposed amplitude model. The experimental results indicate that the simplified pathloss model has a better correlation with the measured radiation pattern. This confirms the higher modelling accuracy of the proposed model.

Due to the multipath phenomenon, low-angle target tracking in radar systems has been a significant challenge as it interferes with the radar's main beam. In this paper, a novel method is proposed to enhance the accuracy of target elevation angle measurement for monopulse radars when encountering multipath propagation phenomenon. This method enhances the accuracy of target angle measurement in the Amplitude Comparison Monopulse (ACM) method by adjusting the outcomes utilizing a coefficient. This coefficient represents the solution to an equation that links the target angle computed through the ACM method and the real-time indication of the influence from multipath interference in the received data. The method offers an accurate estimation of target angles without requiring prior knowledge of meteorological conditions and terrain parameters. The effectiveness of this method in tracking targets at low angles is demonstrated using empirical data, which shows promising results.

This paper investigates the feasibility of obtaining a horizontal wind velocity vector from 77 GHz automotive Frequency Modulated Continuous Wave (FMCW) radar measurements based on reflections off of suspended water droplets. To that end, a dedicated Eiffel-style wind tunnel is constructed with the ability to inject fine water droplets into the air stream. Wind tunnel design is constrained to a low-cost easy-to-build philosophy, avoiding large metal components where possible to reduce unwanted radar reflections. Estimation of the 2D horizontal wind vector is based on the Velocity Azimuth Display (VAD) method utilizing a least-squares approach. The implementation is first verified and tested using a simulated precipitation scenario. Afterwards, the estimation scheme is applied onto real radar captures from wind tunnel experiments. In both cases, VAD provides acceptable estimates for wind direction and speed.

Recent advancements in radar technology have transformed vital sign monitoring in healthcare, providing non-intrusive alternatives to conventional methods, such as electrocardiography. While previous works have explored various aspects of radar-based vital sign analysis, including signal processing and peak detection algorithms, a clear performance comparison remains challenging due to variations in hardware and operating frequency across studies. This paper focuses on the setup configuration and solutions implemented to improve the reflectivity of the measurement object. The simultaneous measurement capability of two FMCW radar systems operating at different frequencies (24 GHz and 60 GHz) is illustrated, and the flexibility of the installation is highlighted, allowing arbitrary chest wall displacement functions via a pressure pump. Both radar systems exhibit the capability to capture stable and high-quality signals, facilitating a subsequent comparative analysis of two heartbeat estimation algorithms.

This paper describes a novel approach based on a combination of MIMO and adaptive Doppler beam sharpening beamforming techniques to enhance radar resolution in dynamic maritime conditions followed by an implementation of a multi-target tracker based on extended Kalman filter to track dynamic targets, thereby, providing higher levels of autonomy to small and medium sized marine crafts. The experiments have been conducted using compact 77-GHz automotive radars in open-sea conditions (sea state 3) and results show reliable performance in detecting and tracking approaching wave using developed signal processing scheme despite platform and sea motion.

This paper investigates the use of the Radon transform for improving small target detection by radar in a marine environment. The data used were collected using a 150 GHz radar staring at targets floating in a wave tank, which replicated maritime conditions. The Radon transform treats the augmented range-time profiles of various targets embedded in sea clutter as images. After transforming these images, in Radon space a method is developed to separate the normative form of the sea clutter from the anomalous forms of the targets, after which the normative form can be reduced. The proposed processing technique shows consistent improvements of up to 12 dB in the SCR.

This paper presents the study on hemi-spherical dielectric lens to minimize the divergence angle of orbital angular momentum(OAM) beam. A four element UCA antenna is designed to generate +1 OAM mode and eight element UCA antenna is designed to generate +2 and +3 OAM modes at resonating frequency of 5.2 GHz WLAN band. The hemi spherical Teflon lens (dielectric constant 2.1) converges the beam direction of UCAs from ± 29 degree to ± 12 degree for OAM mode +1, from ± 25 degree to ± 12 degree for OAM mode +2 and from ± 44 degree to ± 18 degree for OAM mode +3 and simultaneously increases the directivity from 4 dBi to 12 dBi while maintaining side-lobe level below 14dB. A comparison of the proposed hemi-spherical lens with reported lenses in terms of gain, beam direction and side-lobe level are also tabulated.

In this study, loading stub technique is proposed to convert a wideband 2 × 2 full metal cavity-backed antenna into a dual band antenna for satellite communication (SatCom) systems. Wideband 2 × 2 cavity-backed antenna is modified to dual band antenna by only adding conventional coupling slot structure with stubs, which provides filtering. The filtering antenna does not change the wideband antenna's lateral and longitudinal dimensions, and not distort gain and radiation characteristics within in-band frequency regions. By integrating these stubs, undesired frequency band of 12.5 - 13.75 GHz being between Rx (10.7 - 12.5 GHz) and Tx (13.75 - 14.5 GHz) in-bands at Ku-band is effectively suppressed, which improves isolation and lowers interference. The simulated fractional bandwidths (FBW) for |S11| <-10 dB is 15.78% (10.68 - 12.51 GHz) and 8.1% (13.74 - 14.9 GHz) at the Rx and Tx bands, respectively. The peak gain values range from 13.06 to 13.92 dBi at Rx and 13.57 to 14.24 dBi at Tx bands. Besides, out-of-band rejection level reaches to 20.7 dB at 13 GHz while covering the entire Rx and Tx bands of the Ku-band.

In this paper we present the technique of calculation an antenna weights taking into account the phenomenon of mutual coupling between radiating elements of an antenna array. As a result it is possible to recover the Ideal DFT (Discrete Fourier Transform) beams maintaining properties related to orthogonality and high isolation.

In this paper, a dual-polarized antenna for small terminals is investigated. The antenna consists of a feed network that provides excitation to the terminal's metal chassis or the Printed Circuit Board (PCB) ground plane. Feed points are selected based on the Theory of Characteristic Modes. The proposed antenna is a 4-layer PCB with dimensions 80 x 80 mm. It operates within the bandwidth of 1820 - 1880 MHz with polar discrimination of 30dB, directivity of 4.4dBi, and envelope correlation coefficient not exceeding 0.001.

In this paper, we present a setup based on Plano-Concave Fabry-Pérot Open Resonator (PC FPOR) suitable for metallic sample measurement of conductivity ranging from 10^3 S/m (e.g., carbon-fiber-based laminates) up to 10^7 S/m (e.g., good room-temperature conductors like copper). As multiple TEM00Qmodes are considered within the cavity, the setup delivers the properties of the sample-under-test at multiple frequencies in the band of 30 to 70 GHz with separation of ca. 1.5 GHz between consecutive frequency points. This work is an extension of our recently published method towards higher frequencies. Therefore, additional loss sources must be introduced to the cavity's numerical description to cover this range properly. Firstly, volumetric losses of air can no longer be neglected as below 40GHz, especially due to the oxygen absorption peak located at ca. 61 GHz. Secondly, the influence of both coupling holes has to be accounted for. Such a calibration is necessary to measure without additional systematic errors.

This summary presents initial results of the EUREKA-Eurostars 5G_Foil project aiming at the development of industrial screening methods for copper foils for high-frequency applications. Here, a technique based on Ruby Dielectric Resonator is validated for fast determination of effective microwave conductivity, which is then correlated to the foils' surface topology. A high correlation is demonstrated between the measured conductivity and the Developed Interfacial Area Ratio (Sdr), with an excellent fit to a decreasing exponential function. The coefficient of determination decreases when other roughness parameters are taken as a reference, and foil thickness is irrelevant, in the considered thickness range.

A rapidly increasing need for high-speed cable assemblies prompts the need for microwave characterization of wires at frequencies well beyond a few GHz. Therefore, the resonant method based on a cylindrical cavity resonator is presented in this paper, which allows measuring electric conductivity of wires with the diameter less than 1 mm at frequencies spanning from 20 to 40 GHz. The concept of the measurement altogether with the error analysis is addressed and practical limitations of the method are discussed.

In the rapid development of microelectronics, energy, and automotive sectors, as well as Radio-Frequency (RF) telecommunications, the pollution from Electromagnetic Waves (EWs) is perpetual. Electromagnetic interferences (EMI) cause destruction and disruptive impacts on equipment and systems, affecting both ordinary use and specialized, expensive instruments utilized in research facilities. The EMI may lead to unreliable signals and radio frequency (RF) interference. Materials capable of neutralizing EMI effects are essential to minimize deterioration caused by undesired currents and voltages, instrument blockage, incorrect results, and to minimize measuring time. The GrInShield project aims to solve the aforesaid issues by creating innovative shielding graphene-based nanomaterials that are resistant against EMI.

This manuscript investigates the impact of substrate properties on sheet resistance measurements using a 10 GHz scanner employing an inverted Single Post Dielectric Resonator. Our study focuses on carbon coatings deposited on quartz wafers, utilizing retro-modelling to predict the effects of variations in permittivity and thickness of the substrate. Through experimental analysis and predictive modeling, we elucidate the substrate's influence on sheet resistance, providing practical guidelines for thin film measurements on different substrates.

We present a microwave-to-optical converter device based on six-wave mixing in rubidium vapors. We demonstrate a coherent upconversion of microwave radiation at 13.9 GHz frequency to an infrared beam at 776 nm wavelength. Using single photon detection we demonstrate the readout of converted single photons at 3.1% atomic efficiency. The converter exhibits an instantaneous conversion bandwidth of 16 MHz, a tunable bandwidth of 59 MHz, and an operational dynamic range of 57 dB. At the lower end of conversion working range we are able to demonstrate the conversion of free-space microwave thermal photons.

Measurement of on-chip circuits and devices requires accurate calibration methods. Selecting an appropriate calibration for a broad frequency spectrum from MHz to THz while being traceable directly to SI is challenging. The multiline Thru-Reflect-Line (TRL) calibration method is a promising candidate for on-wafer measurements, however due to spatial requirements for standards its use can be limited only to higher frequencies. This study presents comparison of footprint of TRL calibration sets as well as influence of different conductor material. We show that the calibration error can be reduced by using bigger difference between longest and shortest line while conductor material plays a less significant role.

This short communication gives an overview of a beam-steering time-modulated antenna array (TMAA) featuring the widest bandwidth and the finest beam steering among all TMAAs presented in the literature. The design does include any phase-shifters. Instead, the beam steering is achieved by periodic switching of antenna excitations in the feeding network. Results of measurements show, that the TMAA provide similar beam-steering functionality as conventional phased-array; however, without the need of high-resolution phase-shifters.

A novel design method for terahertz (THz) diffractive optical elements is presented. The algorithm utilizes a dedicated diffractive convolutional neural network to emulate radiation propagation and optimize the designed structure's phase delay map. Two-focal-spot THz lenses operating at 140~GHz have been designed using the proposed and referential methods. Both structures have been manufactured using FDM 3D printing and verified experimentally. The neural network-based algorithm allowed to obtain new, unintuitive shapes of optical elements.

The Free Electron Laser in Hamburg (FLASH) has been used for almost 20 years. In 2017, it was decided to perform a program of significant improvements and upgrades to the system to provide better beam performance and maximum energy. One of the upgrades was the complete redesign and delivery of the Main RF Reference Oscillator, RF reference distribution, and frequency conversion components, forming a new RF reference generation and distribution system for FLASH. The modules designed by ISE, in cooperation with DESY, present significantly better performance in terms of phase noise but are also significantly smaller and thus easier to maintain, service, and redesign for other facilities and RF frequencies. Based on already published materials, this contribution overviews the designed RF system components.

In continuation of our work, this paper describes further steps towards the detection remote-based technique for cardiac motion monitoring using a flexible transmitarray antenna operating at 5.8 GHz. Using a self-injection-locked radar, we conducted measurements across four distinct chest locations. Our analysis of the collected data reveals significant disparities in the signal amplitude and waveform characteristics at different chest positions. These findings underscore the influence of the specific location of the chest on radar signals, providing more detailed insight into the complex heart motion patterns. Our findings highlight the importance of considering chest positioning when deciphering radar-derived cardiac monitoring data. This understanding is vital for the advancement of more accurate and efficient techniques in cardiac healthcare, using the capabilities of radar technology for sophisticated medical purposes.

This contribution presents a measurement system for tracking fixed-wing unmanned aerial vehicles (UAV) during gear-less landing on automated, mobile, and rail-based runways. It relies on a transmitter located in the UAV and six-port-based angle-of-arrival measurements. A demonstrator operating in the 24-GHz Industrial, Scientific and Medical (ISM) band is designed, manufactured, and characterized. It guarantees a precision better than one degree, and up to 0.02 degree in optimal conditions as well as real-time capabilities with 500 samples per second. A real-world proof-of-concept experiment validates the approach.

This contribution investigates the accuracy of interferometric continuous-wave radars depending on their own radar cross section (self-RCS) in the context of mechanical vibration analysis. The self-RCS is determined by the overall physical entity of the system including the radar antenna as well as the housing. The backscattering by the radar re-illuminates the target, which ultimately leads to a nonlinear dependency between its motion and the measured phase. This nonlinear distortion is studied in theory and validated by measurements demonstrating phenomena such as harmonic generation and intermodulation, which depend on the self-RCS.

This paper presents a concept of an automatic defect detection system in ballistic inserts utilizing time-domain spectroscopy (TDS) scanner. Measurements were conducted using a fast terahertz scanner based on electronically controlled optical sampling (ECOPS). In the defect detection stage, methods including histogram analysis were employed, enabling automatic detection of defects within ballistic inserts.

This paper proposes a fully integrated simulation environment for an FMCW radar system in an indoor environment operating at 60 GHz. The simulation of the entire signal processing chain, starting with a CST simulation of the antenna pattern and extending to the radar signal processing, enabled the demonstration of the radar hardware's and the channel's inherent properties. Measurements and simulations have revealed the inherent fluctuation paths of a human target by showing a variation of 10 dB in the reflection power of the human in measurements. Our results demonstrate that synthetic datasets can be considered valid alternatives in radar detection. The channel properties can be examined by investigating different up-tilt configurations, and problems such as ground reflections caused by side lobes and multipath propagation within the human target can be further investigated.

This work presents the comparison of the commonly used B-scan imaging method with a delay and sum (DAS) beamforming algorithm in ground penetrating radar (GPR). Utilizing an implemented ultra-wideband (UWB) stepped frequency GPR, using only in-phase data, real-world measurements are compared and discussed. The reduced complexity of the proposed system could increase the speed of data acquisition and processing as well as reduce system cost while providing similar measurement accuracy. This could be of interest for applications such as the localization of underground utility piping, archaeology or mine detection.

Change detection is a vital task in remote sensing analysis. One of its useful aspects is disaster assessment. Synthetic Aperture Radar (SAR) can provide images in all weather conditions, which is beneficial for detecting changes. An unsupervised approach is proposed in this study to learn representations of SAR data and used the encodings from adjacent timeframes to differentiate event-specific changes. The Autoencoder trained on flood images was capable of detecting changes from other events such as wildfires and landslides as shown by a high AUPRC score. Distinct changes for each event results in event-specific threshold value that optimizes the binary change detection task.

When Frequency Diverse Array multiple-input multiple-output (FDA-MIMO) radar implement coherent accumulation detector for moving targets, it is easy to encounter the across range unit (ARU) effects. Besides, due to the frequency offsets across adjacent array elements, serious Doppler spread (DS) will occur between received channels, making it impossible to be coherently accumulated and dramatically reducing the detection performance of the system. Aiming at this issue, a method of FDA-MIMO Radar motion target detection based on Radon-Fourier Transform (RFT) is proposed, that is Two-Step RFT (TSRFT). Firstly, the received channels are divided into two parts for conjugate multiplication, which achieves multi-channel accumulation before RFT. Then RFT is used to obtain a rough estimate of speed and reuse the speed estimation value for 1D-RFT target detection, which reduces computational complexity compared to using traditional RFT. Simulation results reveal that the proposed method improves detection performance by suppressing DS and ARU effects.

In the dynamic landscape of wireless communication, spectrum sensing algorithms play a crucial role in the evolution of Cognitive Radio Networks (CRNs). As CRNs adapt dynamically to varying spectrum conditions, robust spectrum sensing becomes pivotal. In the realm of spectrum sensing, accurate estimation of noise power is paramount for reliable decision-making. Three distinct methods for estimating noise power are: Daubechies wavelet-based methods, Bayesian methods and Median filtering which is, a non-parametric method, proves effective in estimating noise power by analyzing the central tendency of signal samples. The forthcoming analysis will contribute to the understanding of spectrum sensing algorithms within the context of CRNs, aiding in the selection of the most effective method for real-world applications.

The increasing problem of space debris from more satellite launches poses a significant risk to spacecraft and critical satellite operations. This paper looks at the need for better ways to detect and keep track of space debris to prevent collisions. We review different methods like space-based sensors, computer models, and ground radars, all of which have challenges, including missing coverage, difficulty detecting small debris, and complex calculations. Our study focuses on bistatic radar as a way to better search for debris by looking at distance, speed, and acceleration in space. Using Monte Carlo simulations, we aim to track small debris more accurately, helping to manage space traffic and avoid crashes. Our results show that improving bistatic radar settings could greatly help find small debris, making space safer for satellites and spacecraft.

Secondary Surveillance Radar systems play a pivotal role in aviation safety, relying mostly on the Mode S signal format for aircraft tracking. However, challenges such as garbling persist due to overlapping responses from different aircraft, particularly affecting passive surveillance systems. To address these issues, approaches like spectral inverse filtering have been proposed in authors previous work [1] for simpler Mode (SIF/IFF) signal formats. This paper explores the theoretical background and practical implementations of spectral inverse filtering within the context of Mode S signal processing, aiming to mitigate garbling effects and enhance radar data extraction capabilities.

In the article, we evaluate the possibility of locating modern tactical radio using the Signal Doppler Frequency (SDF) method. Using an acoustic signal, we show how to emulate the Doppler effect in laboratory conditions. We use the L3 Harris AN/PRC-152A tactical radio as a transmitter. The research is carried out on the proposed concept of building a location sensor. We test a software-defined radio (SDR) platform that can be used in SDF-based localization. We use SDR with low size, weight, and power consumption that can be mounted on an unmanned aerial vehicle (UAV). We show the localization accuracy results for different carrier frequencies emitted by the radio.

Radar target detection based on information geometry theory is a new detection technology. This method transforms the problem of target detection into the problem of distinguishing target and clutter on the manifold. The target and clutter metrics are performed on the echo-built manifold, which is advantageous for detection under low SCR conditions. In practical application scenarios, Weibull-distributed clutter and K-distributed clutter are important distributions for describing clutter.Therefore, based on matrix information geometry (MIG) detectors, this paper analyzes the performance and summarizes the performance differences of MIG detection methods under the two clutter backgrounds. Finally, the parameters of the simulation clutter data are changed to analyze the performance changes of different matrix CFAR. The results show that as the different parameters of clutter vary, the longer the trailing of the clutter probability density function leads to a degradation of the detection performance. This will facilitate the selection of appropriate metrics for different clutter environments.

This paper presents the design of a compact, programmable X-Band multi-channel receiver used for Doppler Weather Radars Systems by combining two different gain channels, called high gain and low gain channels, to achieve the required high dynamic range of 100dB. Gain differences between these two channels and linearity in output power are maintained such that during processing of these differential channel gains a smooth transition between channels is achieved. This paper also describes a unique mechanical design structure of the receiver, with a 2-deck approach in order to maintain high isolation between the channels. An inbuilt microcontroller circuitry is provided for controlling and monitoring the receiver through Ethernet thereby providing an on-the-go gain and phase matching facility for the radar system during receiver operation without disturbing any hardware. The major specifications achieved are isolation between the channels of 65dB (min), noise figure 1.8dB max, gain matching ± 0.4dB, phase matching ± 10° and receiver sensitivity of -112dBm for IF level output of 3dB above noise floor. The module has been realized & tested, to meet all the target specifications successfully, and has been integrated in the X band Doppler Weather Radar system.

The orbital angular momentum (OAM) beam has shown great prospects of radar applications, due to the OAM diversity characteristics. However, the radiation energy convergence is still a hard problem to be solved for radar target imaging in realistic scenario. In this paper, a novel OAM beam generation method is developed based on the uniform circular array (UCA) and phase coded waveform, which can collimate the beams with different OAM modes. Furthermore, the echo demodulation and the imaging methods are proposed to reconstruct the target profiles in the range and azimuth domain. Simulation results validate that the OAM-based radar imaging can achieve higher azimuth resolution than the conventional real aperture imaging. This work can advance the development of vortex wave radar technology and radar system.

Unmanned aerial vehicles (UAVs) have become more accessible and widely used, with applications ranging from military surveillance to weaponization. Because of their impressive speeds, maneuverability, and ability to evade detection, small and agile UAVs present significant challenges to traditional interception methods. Directed energy weapons (DEW) are a highly effective countermeasure that is currently undergoing extensive research and development. High-power electromagnetic effects can significantly impact electronic systems. These effects can lead to poor operation, circuit malfunction, or complete failure of electronic devices. High-power electromagnetic fields, such as those generated by microwave weapons, can induce unwanted currents and voltages in electronic circuits, leading to the disruption or destruction of semiconductors, microchips, and other electronic components. However due to difficulty of detecting small UAV's and their speed the time for counteraction, never minding decision making, is extremely short. This characteristic render DEW pointless if sufficient intensities for certain impact on UAV are not generated at once. However the spatial distribution of microwave radiation can be unpredictable and random scattering and interference can cause unexpected distributions and the negative effects of electromagnetic fields on people and the environment were first observed at the end of the nineteenth century. This paper provides findings on the efficacy and thresholds of high power microwave pulses on UAVs, as well as their impact on cells cultures in a controlled laboratory setting. Methods An investigation into the impact of high-power microwaves (HPMs) on AVs and cells cultures was conducted. A research study utilized an impulse compressor-based HPM generator. This source produces a sine wave with a frequency in the range of 2995-3003MHz. The generating tube is supplied with electricity from an HV modulator based on PFN (Pulse Forming Network) technology, i.e. a pulse forming line connected to a specially designed impulse transformer. The microwave tube producing microwave radiation is connected through a matched microwave waveguide filed with sulfur hexafluoride (SF6) or nitrogen to the radiation emitter, which may be a parabolic antenna or a horn (cone) antenna. Compression enables the generation of impulses with a field magnitude of up to 50 kV/m and a power of 3MW. Employed measurement stands included an HPM generator in both land and sea setups on military training grounds, as well as reverberating and anechoic chambers in laboratory. Conducted tests included analyzing the response of UAV and its components when subjected to intense HPM radiation. High-power d-dot and b-dot microwave probes were utilized, along with field intensity loggers, to measure and analyze generated filed distributions. Marx's generator coupled with TEM cell enabled the generation High Power ElectroMagnetic (HEMP) impulses of fields as high as 2 MV/m which give insight on impact high voltage transient pulses with wide and/or very wide bandwidth (HV-WB/UWB) on living organism on molecular level for determining the biological mechanisms of phenotypic and genotypic changes occurring under the influence of these kind of weapons on human resources. The HEMP pulses impact was conducted on four types of mammalian cells: Leydig cells from the male gonadal interstitium, mesenchymal stem cells (hMSC), skin fibroblasts and prostate cancer cells. The HPM pulses impact was conducted on five types of mammalian cells: Leydig TM3 cells - a line derived from the interstitium of mouse testes, human epithelial cells from the lens of the eye, human fibroblasts from the skin, neuroblastoma cells derived from the rat nervous system and human epithelial cells derived from prostate cancer. Results The experiments presented instances of both soft and hardkill UAV loss caused by HPM impulses. The results of experiments show that field magnitudes above 50V/m can cause softkill effects, also referred as lock-up, which translates to UAV systems are unable to operate and inevitably crash. Furthermore, burnout effects were repeated at intensities above 50kV/m. These effects were partly caused by the destruction of electronic components by heat and discharge arc. Plasma formation was repeatedly induced with a tealight candle used for a light source in reverberation chamber. Additionally, the researchers report instances where radiation directly damaged the structure of UAV mechanical parts. The failure of faraday shields due to structural flexing has been illustrated in the discussion, which indicates that directed microwave weapons are a suitable countermeasure against unwanted UAVs. HEMP pulse research has revealed a number of transient changes in life processes with no alteration in DNA content. HPM pulse research shows changes in DNA of healthy cells reversible after 4 hours and changes related to mitochondria that affect, among others, on the energy state of the cell and cell cycle control. Findings shows intensive cell division of the examined prostate cancer cells and neuroblastoma cells as aftermath of HPM irradiation. Conclusions The study's findings emphasize the effectiveness of HPM pulses as a practical method for defending against unauthorized UAVs. Through the utilization of advanced techniques for precise control and manipulation of electromagnetic radiation, it becomes feasible to render UAVs ineffective by exploiting their electronic and structural weaknesses. Current microwave technology can address tread that unwanted militarized UAV pose. To ensure the reliability of HPM weapons as effective shields against UAVs, it is crucial to address the implementation of a suitable beam control system and the ability to adjust the generator system to scale the radiation intensity regarding the desired impact. The findings from experiments evaluating the genotoxic effects following exposure to pulsed electromagnetic fields at microwave frequencies, with varying physical parameters, remain uncertain. The majority of research efforts have not found evidence of direct genotoxic or mutagenic effects following this particular type of exposure to different types of cells within a short period of time. It is worth noting that the analysis of these results should take into account the limitations arising from the differences between the in vitro and in vivo environments, potentially impacting the interpretation and generalization of the obtained data. Nevertheless, presented results shed light on aspects that should be further investigated in this context.

This paper investigates the integration of pilot carriers into Golay complementary sequences for peak-to-average power ratio (PAPR) reduction in joint radar and communications (JRC) systems employing Orthogonal Frequency Division Multiplexing (OFDM) waveforms. While using Golay sequences as OFDM codewords allows to achieve PAPR values below 3 dB, the insertion of pilot tones can disrupt their optimal properties. Two approaches are proposed to address this challenge: restricting the transmitted codeword set to Golay sequences sharing desired pilot tone configurations or forcing predetermined pilot sequences onto Golay sequences to create Quasi-Golay sequences. Analysis reveals a trade-off between PAPR reduction and communication throughput: the Golay-based approach offers optimal PAPR but reduced data rates, whereas the Quasi-Golay -based approach provides higher data rates at the expense of slightly higher PAPR values. Evaluation through simulations demonstrates the performance of these approaches and their implications for JRC systems. This study underscores the importance of careful consideration of pilot carrier integration in Golay-based PAPR reduction techniques for efficient JRC system design.

The integration of wireless communication and radar sensing is gaining the interest of researchers from wireless communication and radar societies. Sensing in Integrated Communication and Sensing (ICAS) systems differs from the traditional radar system in the configuration of transmitter-target-receiver, the operating frequency bands, and the transmitting waveform. It is necessary to understand how target electromagnetic signatures behave in this context. Therefore, this paper presents measurements and analysis of two important target signatures, reflectivity and micro-Doppler, for sensing in ICAS. These target signatures are measured in the state-of-the-art measurement system, Bistatische-Radar-Messeinrichtung (BiRa).

A future design goal for 6G networks is the possibility to use the transmitted OFDM signal also for sensing applications beyond the communication purpose. The transmitter, which probably provide the highest power, are base stations, but in case of uplink or sidelink transmissions the radiation of user equipment can also be used. This leads to bistatic radar configurations with moving transmitter and receivers, where the underlying use case is the installation of user equipment on drones for target detection. The achievable accuracy is derived in this paper for multi-static measurements and tracks. The position of non-cooperative transmitters can also be determined with passive emitter tracking (PET) receivers. Both type of measurements can be fused by Kalman filtering. Besides target detection the operation as bistatic synthetic aperture radar is a interesting use case in order to generate images of the ground. This requires an assessment on the constraints for valid transmitter and receiver configurations.

The hyperbolic fractional Fourier transform (HFrFT) as a generalized form of the fractional Fourier transform (FrFT) based on complex transform orders is introduced. This paper defines the continuous-time hyperbolic fractional Fourier transform (CHFrFT). Further, a closed form of the discrete hyperbolic fractional Fourier transform (DHFrFT) is derived. The ambiguity function (AF) of the HFrFT signal is calculated, mathematically. The performance of the proposed transform in radar signal processing by analyzing the AF and in wireless communication systems based on the bit error rate (BER) analysis, is evaluated. The simulation result shows that HFrFT can be a suitable technique in joint radar and communication (JRC) applications.

This work proposes a novel approach to advance non-contact millimeter-wave sensing capabilities through the fusion of microwave characterization techniques with nanorobotics. Firstly, we introduce a WR15 waveguide six-port radar operating around 60 GHz for precise measurement of free-space reflection coefficients. Precise knowledge of the standoff distance between the antenna and the material under test (MUT) directly impacts the accuracy for extracting electromagnetic properties of the MUT. Therefore, the MUT is mounted on a piezoelectric nano-positionning stage with resolution of ± 30nm over a centimeter-scale distance.

In this work, new ultra-low temperature co-fired glass-ceramic composite intended to serve as a dielectric substrate for microwave and millimeter wave applications is investigated. The new material is subject to characterization of dielectric properties in a wide frequency spectrum using resonant methods and time domain spectroscopy. The presented measurement methodology involving different measurement techniques and frequency ranges allows for comprehensive characterization of new ceramic materials at consecutive development stages, supporting optimization of a fabrication process. Dielectric constant (loss tangent) of the newly developed ULTCC substrate, which is intended to be lower than 15 (0.01), creates a perspective for its future application as dielectric substrates for electronic systems.

A Fabry-Perot open resonator has become a versatile tool for the broadband room-temperature microwave characterization of various kind of materials, including dielectric films, low-loss liquids and metals. An emerging need for the measurements at elevated temperatures has prompted the study of its thermal properties presented in this paper. It is shown that the Fabry-Perot open resonator as an ultra-sensitive fixture is capable of quantitatively detecting such barely visible effects as changes of the air refractivity with temperature and humidity. In addition to that, it is shown how the effective electric conductivity of silver-plated spherical mirrors changes with frequency and temperature. The study is concentrated on a double-concave geometry of the resonator operating in the 14-50 GHz range.

The paper presents the electromagnetic modelling and mechanical considerations for the design of a Balanced-type Circular Disk Resonator (BCDR). The purpose of the work is to develop a robust in-house methodology for measuring the out-of-plane component of complex permittivity of materials at microwave and mmWave frequencies. In this summary, a novel concept of a thick central electrode manufactured as a pair of discs on a double-sided PCB substrate is proposed, evaluated by modelling, implemented, and validated in a BCDR prototype.

The paper presents a comparison between transmission/reflection (T/R) and resonant methods employed for the characterization of complex permittivity of high-loss liquid. The liquid under test is 50% aqueous solution of propan-2-ol. The T/R method with a meniscus-removal algorithm utilizes a 7 mm coaxial line in a semi-open test cell configuration and the complex permittivity is measured in 0.2-18 GHz bandwidth. For the resonant method, a dielectric resonator cavity operating in TE01delta mode at a nominal frequency of 2.45 GHz is utilized. For both methods, the dielectric constant and loss tangent of the 50% aqueous solution of propan-2-ol are extracted revealing good agreement of the obtained results and confirming their applicability for the characterization of high-loss liquid materials.

This paper is a brief description of the results presented in 10.1109/LMWC.2022.3154532. The Finite-Element Method (FEM) is applied for modal analysis of ferrite-loaded spherical resonators. To improve the efficiency of the numerical calculations, the body-of-revolution (BOR) technique is utilized. Due to the frequency-dependent ferrite permeability, FEM leads to a nonlinear eigenvalue problem that is challenging to solve. To this end, Beyn's method is proposed. The effectiveness of the proposed approach is confirmed by comparing with the results obtained analytically and with the measured data.

A tunable, polarization sensitive microwave filter based on a reconfigurable dual-layered two-dimensional metallic photonic crystal is presented. The filter consists of a metallic plate with periodic holes and metal pillars which are anchored in a substrate material. The diameter of the pillars is smaller than that of the holes and the lateral position of the pillars with respect to the holes is tunable. We study the transmission of the device for linearly polarized electromagnetic radiation, which is polarized parallel and perpendicular to the displacement of the movable membrane, respectively. The tuning range spans from 20.18 GHz to 26.58 GHz for perpendicular polarization and from 20.18 GHz to 18.42 GHz for parallel polarization. The 3 dB operation bandwidth varies between 3.82 GHz and 6.44 GHz for perpendicular polarization and between 3.42 GHz and 3.82 GHz for parallel polarization. Experimental data are in good agreement with finite element method (FEM) simulations.

In our recent work [1], we introduced a new type of frequency-variant reactive coupling (FVRC) circuits for coupled-resonator filters. The FVRC circuit consists of a bridged-T network with four reactive components. This circuit has a highly nonlinear frequency-dependent transimpedance characteristic and can be used as an in-line coupling between two resonators, creating up to one transmission pole and up to two transmission zeros. For this reason, this new class of frequency-variant coupling is called double zero single pole (DZSP) coupling networks. The number and location of the poles and zeros depend on the component types and values in the bridged-T network. The transmission zeros can be located below, above, or on both sides of the pole. Moreover, some configurations allow independent control of the zero positions. The transmission pole is located in the passband of the filter, increasing its order. The transmission zeros can be placed on the imaginary axis to improve the selectivity of the amplitude response, or as a complex pair of zeros to shape the group delay profile. We propose six types of DZSP circuits based on the number and location of the poles and zeros they generate. The FVRC circuits can significantly improve the filter response allowing for developing compact in-line microwave filters with increased selectivity or improved group delay profile. However, achieving these characteristics requires an efficient method for filter synthesis. The first step in the synthesis is finding the characteristic polynomials of the target response, which can be done using an analytic method or an optimization-based approach. The filter is then represented by its coupling matrix with FVRC acting as non-ideal frequency-variant inverters. The FVRC circuit itself is represented by its impedance matrix of a two-port network. The next step is to find the values of all entries in the coupling matrix to achieve the desired response. Since the coupling matrix entries are nonlinear functions of frequency, this step involves solving an inverse structured nonlinear eigenvalue problem (ISNEVP) [2]. Once the coupling matrix of the filter has been found, we proceed to the final step of implementing the filter in a chosen technology. FVRCs can be implemented in waveguide and microstrip technologies. In microstrip technology, we use shorted or open-ended stubs, coupled lines, and transmission line sections, while in waveguide technology, we use posts of incomplete heights and various shapes. The proposed method is validated with several examples of filters with FVRC circuits. We show two variants of a third-order filter with FVRC that introduces one pole and two transmission zeros below (variant I) or above (variant II) the passband, with simulation results of waveguide implementation and fabricated circuits in microstrip technology for each variant. A microstrip fifth-order filter with four transmission zeros (two on each side of the passband) has also been fabricated and measured. The obtained results show a good agreement between the target and the simulated or measured responses.

The electromagnetic coupling is analyzed from the point of view of forces between coupled fields and coupled resonators. The electromagnetic couplings always change resonant frequencies of coupled resonators as well as impedances of coupled transmission lines. Even more important is that electromagnetic couplings always create forces that work in the same manner as gravity forces under the condition that two coupled modes are exited simultaneously. The forces between coupled resonant modes are calculated for typical rectangular cavity resonators. It can be shown that E-M coupling can be related to the gravity force.

The range of air targets encountered in air-to-air radar modes is evolving. In addition to airliners or fighters, it also includes a broader range of platforms such as furtive targets or drones. Additionally, the frequency band used by modern waveforms is also widening. These changes raise the question of the relevance of Swerling models to evaluate radar performance. In this article, we compare different fluctuation models and their associated detection performance, using measured data both in flight condition and in anechoic chamber. We show that the Swerling model remains well suited for the simple case of a face-to-face target, even an atypical one, within a limited band. However, generalizing it with the Generalized Pareto model makes it possible to take into account the diversity of the presentation angles of the target, and the widening of the transmission band

The problem of aliasing in precipitation Doppler spectrum with uniform pulse repetition time is addressed. This study focuses on de-aliasing such Doppler spectra using non- uniform sampling techniques, namely, Log-periodic and Periodic non-uniform sampling. These techniques reduce the ambiguous main lobes caused by aliasing (by going beyond the observable frequency limit) into ambiguous sidelobes that are distinguishable from the original spectra. The SNR is further enhanced by using an Iterative Adaptive Approach (IAA) algorithm. The performance of Doppler moment estimation is presented after applying the IAA algorithm on simulated precipitation-like radar echoes. However, the ambiguous sidelobe suppression is highly dependent on the spectral width of the Doppler spectra.

Inverse synthetic aperture radar (ISAR) technique allows to obtain high resolution images of observed objects that are moving with respect to the radar. This may be an added feature to an air defense radars helping in classification procedure of the objects. Air defense radars in surveillance modes usually employ low pulse repetition frequencies (PRFs), which cause the echo signal spectrum to be ambiguous in Doppler frequency domain. Depending on the radar central frequency, the object's velocity and the PRF the duration time of the Doppler-unambiguous raw signal can be relatively short, reducing the obtainable resolution of the ISAR image, and there may be several spectrum aliases that would result in ghost targets in the image. In this paper a method of extending the Doppler frequency unambiguity range in a low PRF radar by up-sampling the raw ISAR signal is presented. The proposed method utilizes the spectrum concatenation, rotation and filtering to eliminate aliases in the frequency domain. Thanks to this a long unambiguous raw signal history if available for image synthesis algorithms.

Orthogonal frequency division multiplexing (OFDM) waveform is being increasingly used in radar sensing because it enables joint radar-communication system in a single platform. However, the bandwidth of the OFDM radar cannot be sufficiently increased due to the given sampling requirement, which results in limited range resolution. Therefore, additional signal processing needs to be performed to enable accurate sensing of targets. This paper proposes a method for improving the ranging accuracy of the OFDM radar system using interpolation of discrete Fourier transform (DFT) samples. The DFT magnitude ratio of two DFT samples is used to refine the coarse frequency estimate. The simulation results demonstrate that the proposed method can estimate the range of targets much more accurately than the conventional DFT-based method. In addition, the proposed method showed robust estimation performance even when the signal-to-noise ratio is low or when there are multiple targets.

In this paper, beam scanning properties of a constant-index biconvex (BC) lens are explored. It is shown that changing the lens geometry from plano-convex (PC) to BC while maintaining constant focal length, lens aperture, and thickness leads to a 2.1 times increase in the scanning angle (from ±18.11° to ±38.14°) and a 4.3 times increase in the scanning solid angle (from 0.31 sr to 1.34 sr). The utilization of the BC lens also results in a lower lens volume and the overall size of lens antennas, however, at the expense of a maximum gain reduction that is not greater than 2.9 dB. The proposed lenses were printed on a 3D printer and the concept has been validated by the measurements of four-beam lens antenna arrays operating at 24 GHz.

The present paper proposes a new design of a cross-shaped groove gap waveguide-based 3-dB directional coupler for Ka-band applications. We use groove gap waveguide technology for high power handling and to avoid fabrication difficulties of printed and hollow waveguide structures in mmWave bands. The proposed structure exhibits a fractional bandwidth of 30% centers at 30 GHz for |S11| < -20 dB. The phase balance is 90 ± 2.5◦ and amplitude balance of -3 ± 0.5 dB from 26 to 34 GHz. The presented coupler can be considered as a robust option for Ka-band and mmWave applications.

The resonant linear and nonlinear properties in THz range of 2D one in graphene and silicene placed into an external magnetic field are investigated theoretically. The linear resonant dependencies of the tensor complex conductivity are computed from the kinetic theory. When the electromagnetic frequency is close to the cyclotron one, the conductivity increases sharply. The dependencies of the tensor conductivity on frequency coincide with ones obtained from the hydrodynamic theory under realistic electron concentrations and collision frequencies. The same is valid for the nonlinear dependencies of the densities of electric current on the applied electric field. Thus, the nonlinear hydrodynamic equations are valid to describe the nonlinear resonant electromagnetic wave propagation in the multilayer structures dielectric-graphene or silicene.

The assessment of water wave properties in near shore regions is of utmost importance in several applications, such as for tasks like sea state monitoring. This study presents a methodology based on the adoption of a low-cost Frequency Modulated Continuous Wave (FMCW) radar system for extracting information about the wave parameters. This approach offers a reliable means to gather essential information about wave characteristics in near shore areas. The approach has been preliminary assessed through experimental measurements. The obtained findings highlight the capability of the adopted short-range radar to obtain meaningful information about the near-shore sea state.

The work presents an algorithm characterized by high precision and efficiency in identifying signals related to data transmission between the controller and the drone. Using an efficient change point detection algorithm and parallel analysis capabilities, this method facilitates rapid signal analysis. These features make the proposed algorithm a solid basis for developing an effective anti-drone defense system.

This paper presents the basics of the newly-introduced Polish digital time signal service on 225 kHz and its test reception in Lithuania using a prototype receiver. The basic performance of the receiver is presented, along with the definition of the base service coverage in international European scale.

In this paper a linear antenna array utilizing sector radiation pattern is presented. The Fourier transform method is used for synthesis, from which the obtained excitation coefficients determine the resultant radiation pattern for an arbitrary sector. Moreover, the influence of a single radiating element radiation pattern is considered which is used to act as a counterweight to compensate the degradation which occur at the sector boundaries, by modifying the array factor. Theoretical examples for this phenomenon are presented, whereas for the purpose of this paper a nine-element linear array with 90° sector was designed and manufactured in order to verify this concept.

In various microwave heating methods, near-field microwave heating utilizes one or multiple antennas to radiate microwaves onto the heating object. In near-field scenarios, the presence of the heating object may influence the input impedance of antenna. Mismatch between the microwave generator and the antenna reduces radiation power, thereby lowering microwave heating efficiency. This study investigates the influence of the heating object on the near-field radiation of the slotted waveguide. The effects of the distance between the heating object and the slotted waveguide, as well as the dielectric constant of the heating object, on the radiation of the slotted waveguide are examined. Furthermore, methods for improving impedance matching of the slotted waveguide in the presence of a heating object are also proposed.

The construction, simulation and measurement results of the microstrip planar antenna designed for 26 GHz 5G band have been presented in the paper. The antenna was designed on the Rogers 3003 substrate, to obtain high efficiency and parameters stability in the operating band. Project design of the antenna in CST simulation software was made. Based on the design, the prototype antenna array was manufactured in department local laboratory. Basic parameters of the antenna were measured under laboratory conditions. Measured reflection characteristic is similar to simulation results. To analyze signal feed and matching network, simple 2x1 antenna array was designed and practically manufactured. Manufactured prototype antenna has bandwidth about 5,3 GHz with 27 GHz center frequency, so 18,5 % relative bandwidth was obtained. Compared to the classic patch radiators, additional elements such as side slots and shunt-stubs were used. These elements allowed for the expansion of the operating bandwidth.

A 4x4 Butler matrix based switched-beam system with 1x4 horn antenna array is designed and measured. The Butler matrix was developed using metamaterial technology. The measurement results indicate a wide operating band of the device covering the range from 18 GHz to 24 GHz. This system can work both as a transmitter and as a receiver.

The presented work applies optimization methods together to signal prediction models for within the range of urban geography, developing convex graphical analysis. The study proves with numerical results and compared the Log-Distance and MMSE-Mean Least Squared Error equations, the development of polynomial modeling and meta-heuristics. With analysis of the behavior and dispersion of the signal transmitted in a confined environment, and in the study of the response of electromagnetic impulses in free and wooded areas. Geographic coordinates define ideal iteration points through numerical results, demonstrating a new combined method as an alternative in transmission analysis in telecommunications, with expansion in the development of a more complex programmable computerized system for the industry.

Based on our previous work, a brief description of the theory of using TE and TM modes to determine the permittivity of nonmagnetic uniaxial anisotropic media without changing the position of the sample is presented. The extraction procedure is based on the use of two pairs of reflection coefficients and propagation coefficients in a manner similar to the classical Nicolson-Ross-Weir method for isotropic media. The obtained simulation results for an artificial uniaxial anisotropic dielectric material constitute a promising basis for experimental research.

In this paper a new concept of metallic coating and manufacturing is developed based on an already modeled and produced low-cost WR90 Coaxial-Waveguide-Transition (CWT). The difference lies in applying multiple thin layers of aluminum foil and modeling, as well as constructing it in the form of a plug-in kit. The deembedding of the aluminum prototypes reveals the effects of increased conductivity and reduced irregularities in the form of significantly improved reflection and transmission parameters. In conclusion the application of the low-cost concept with ongoing development and further approximation to the simulation can indeed be considered practical.

The article presents kriging as the potential alternative interpolation method for radio received signal indicator distributions. Reference maps of Received Signal Strength Indication (RSSI) are used for indoor localization systems. The study compares two methods of interpolating RSSI radio maps - linear interpolation and kriging. It is verified that for a smaller number of samples selected for interpolation, the kriging method demonstrates higher interpolation accuracy compared to standard linear interpolation.

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This paper presents an active double-balanced mixer circuit achieving 2 GHz to 40 GHz bandwidth, designed in UMS 0.15 μm GaN process. Distributed Gilbert cell topology was chosen to achieve broadband impedance matching along with inherent LO to IF isolation and sufficient Conversion Gain (CG) results with LO power level considerably lower than as required by passive mixer counterparts. Designed as a proof of concept, the circuit demonstrated a flat CG response of approx. −5 dB up to 45GHz when employed as a frequency down-converter and up to 36GHz when used as an up-converter. The LO to IF leakage suppression was better than 19 dB up to 30GHz with no filtering employed. The LO power before starvation was 12dBm, whereas the input referred 1 dB compression point was 11.5dBm and the double sided noise figure was in range 7.6 dB to 12.8 dB.

The paper focuses on non-contact measurement of human vital parameter estimation based on analyzing micro-Doppler signatures of radar signals. The frequency-modulated continuous wave (FMCW) radar operating at a frequency of $122$ GHz was used for measurements. The cadence-velocity diagram (CVD) obtained from the spectrogram and the displacement function obtained by phase demodulation were used in the processing. A measurement process was implemented, human vital parameters were measured, and thorax movement was observed in spectrograms and displacement plots. For the selected measurement, the respiratory and heart rates were determined with high certainty when using the CVD-based method. At the same time, the heart rate is not directly visible in the FFT from the displacement function. The results may help develop a more extensive and robust noise measurement system for continuously observing life activities.

In this paper, the performance of the phase shift keying linear frequency modulated (PSK-LFM) waveform that enables joint radar and communication system simultaneously is experimentally evaluated for moving target detection. The PSK-LFM waveform embeds communication data using multiple PSK symbols into the LFM signal that is commonly used in radar systems. Such waveform is utilized in multiple-input multiple-output (MIMO) array to obtain the angular position information of the targets present in the scene. To simultaneously enable all transmitters in the MIMO array, code-division-multiplexing (CDM) approach is used by assigning unique bit sequences to each transmitter to prevent mutual interference. Further, to achieve enhanced angular and velocity resolutions, the use of Burg algorithm is investigated through experimental data.

This paper focuses on testing the suitability of the USRP B200mini platform for radio emitter localization using the Signal Doppler Frequency (SDF) method. We show how to emulate the Doppler effect in laboratory conditions for different scenarios. For each scenario, we estimate the localization accuracy. We compare our measurement results with simulation studies.

This paper outlines a method for segmentation and classification of ISAR images generated at sub-THz frequencies for the purposes of space domain awareness. Image segmentation is achieved using statistical region merging. Simulated ISAR imagery is segmented into simple regions, which are used to train a machine learning model to predict the classes within a series of test images. The results indicate that the use of support vector machines for statistical inference has great potential as part of a broader classification process, able to use multiple predictors to draw distinctions between a number of classes.

Highly sensitive radars and a more challenging environment lead to more and more clutter detections. The situational picture becomes crowded and overwhelming for the operator. For high Doppler resolution radars we have shown, that micro-Doppler based target classification can be used to distinguish different targets as well as clutter from each other. It is, however, unclear, how well such approaches perform with low resolution Doppler radars (LRDRs) with as low as 8 Doppler bins and a Doppler velocity separation of 6 to 8 m/s to separate flying targets from clutter like birds, insect swarms, wind turbines, and many more. Here, we first present an in-house dataset from an air surveillance radar, associated challenges, and a baseline legacy implementation previously published. Next, we present two state-of-the art models based on convolutional neural networks and transformer architectures and discuss the results. It is shown, that the modern approaches clearly supercede the baseline implementation and achieve a classification performance, that can be used to greatly improve the operational usage. Quantitative evidence as well as situational pictures demonstrating the operational performance improvement are presented.

Next-generation SAR systems will feature high-resolution wide-swath acquisitions, resulting in a significant increase of the onboard data volume to be acquired by the system. This causes severe constraints in terms of onboard memory requirements and downlink capacity. In this scenario, an efficient onboard quantization of the raw data is of utmost importance, representing a trade-off between achievable product quality and consequent on-board data volume. In this paper, we investigate the use of artificial intelligence (AI), and in particular of deep learning (DL), for flexible and on-board SAR raw data quantization. The aim is to derive an optimized and adaptive data rate allocation given a set of desired performance metrics and requirements in the resulting focused SAR image without relying on a priori information on the acquired scene. The obtained bitrate maps (BRMs) can then be dynamically used as input to a state-of-the-art BAQ quantizer to perform the on-board raw data digitization. The proposed method aims at directly linking the characteristics of the SAR raw data to performance parameters computed in the focused SAR domain, without the necessity for performing on-board focusing. For optimizing the proposed DL model architecture, we consider multiple target performance parameters such as the Signal-to-Quantization Noise Ratio (SQNR), the InSAR coherence loss or the interferometric phase error, extending the capabilities of the architecture and, ideally, providing multiple bitrate estimations for a single input scene at a time, depending on the specific application requirement. The proposed method allows for an efficient joint optimization and reduction of the data rate and of the resulting performance setting a new paradigm for data reduction in future SAR systems.

Through-the-wall 3D imaging is promising for concealed human target sensing, as more details can be provided. Conventional imaging techniques, such as the back projection (BP) in multiple-input-mutiple-output (MIMO) through-wall radar (TWR), suffer from poor resolution due to limited aperture and artifacts introduced by grating lobes. In this paper, we propose an imaging neural network based on multi-layer perceptrons (MLP) to enhance TWR image formation performance. The network intuitively takes the radar channel-range profiles as the input and directly outputs high-quality 3D imaging results. It adopts MLP-Mixer as the backbone and effectively integrates features from various channels. Specifically, we design a dataset construction method that utilizes point clouds captured by a stereo camera, providing high-resolution labels and naturally preventing the image from grating lobes and broadening, The network achieves high-quality image formation in real-measured data even with training solely on the simulated dataset. To further mitigate the target flickering, we fine-tune the network using a small amount of real-measured data.

This paper presents the initial steps in validating EM propagation software results to experimental data collected by a passive bistatic DVB-T system. The paper details the validation process of the software, and presents the first results in merging the simulated and SAR data. The early simulation results show good coherence to SAR imagery.

This paper presents an efficient approach to non-iterative and single-snapshot target acceleration estimation in passive radars with a pulse over-the-horizon radar (OTHR) as a source of illumination. The method was developed within iFURTHER, an EU-funded project studying a Cognitive Network of HF Radars for European Defence under the framework of the European Defence Fund. The proposed algorithm's description shows how the target Doppler rate can be estimated for each observed target simultaneously. Next, the method is experimentally validated using the signal recorded by a lightweight software-defined radio (SDR). A non-cooperative target's acceleration was estimated in less than the processing integration time, thus making the presented technique capable of working in real-time.

In this paper we investigate the potential benefits of implementing an adaptive active-passive mode-switching algorithm to a multi-function radio frequency (RF) system for sensing. This research was performed using experimental radar data captured during a trial of a hybrid active-passive capable software defined radio (SDR) based radar. An outline of the system used during the experiment is included within the paper, as well as an overview of the experiment itself. Details of the post-processing performed on the data and results produced from running the algorithm on the experimental data are shown. The performance benefits of a real-time application of the algorithm are quantified and verified in the form of figures and tables. In some cases a 60% reduction in active transmission time is realised, as well as a 20% increase in mean SNR over time when compared with data not implementing the algorithm. The strengths and limitations of the algorithm in its current form are discussed as well as directions for future work.

This article presents unique results of detecting a small rocket in its launch phase using a passive radar in the VHF band using a DVB-T signal. It is shown that such an object, possessing significant acceleration in the initial phase of flight, can be successfully detected by applying appropriate techniques, such as selecting the proper integration time and using an extended cross-ambiguity function. The detection results align with simulations, which demonstrate that propagation effects such as multipath can cause detection fades. Additionally, the launching rocket may have a dynamically changing bistatic RCS, which also affects its detectability.

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Any radar sensor admits an unambiguous field of view outside of which the apparent state of a target does not correspond to its actual one. In order to tackle this issue, this work presents a 3D multi-target detection and tracking approach for resolving radar ambiguity in range, Doppler and angle. First, range-Doppler detection is achieved by combining a foreground detector with a modified constant false alarm rate detector. Next, an extended Kalman filtering with 3D model constant velocity constant heading is implemented. The measurement multiplicity is calculated using maximum likelihood at the innovation calculation step. Lastly, track management using a Bayesian process is presented. All these algorithms have been tested on both real and simulated data so as to assess estimation performance and the ability to resolve ambiguity. An RMSE in position of 0.6m between estimates of radar tracking and GNSS/IMU/wheel odometry fusion was obtained for tracking two rovers covering a total trajectory of more than 70m.

In this paper, we propose a modification to Newton's method designed for solving systems of nonlinear equations that arise in multistatic passive radar systems for estimating the coordinates of detected objects and constructing their trajectories. We investigate and prove the efficiency of using the same Jacobian matrix determinant of partial derivatives for several steps of iteration, which significantly reduces computation time while maintaining the necessary accuracy of calculations. Additionally, we analyze the effectiveness of the proposed method for constructing continuous trajectories of aerial objects during brief losses of their emitted signals. The modified version of Newton's method suggested here is advisable for use in solving coordinate-trajectory problems in passive automatic detection systems and for constructing movement routes of aerial objects.

This paper investigates multi-target tracking with multiple unbiased sensors under complex environments including clutters and false alarms. The goal is to test different data association techniques such as the Global Nearest Neighbor (GNN) method and Joint Probability Distribution Association Filter (JPDAF), which are applied using two different radars. Tracking is also applied with the fusion of multiple sensors based on the JPDAF measurements fusion method and track-to-track Covariance Intersection fusion method. Standard Metrics are used to compare all possible cases with different scenarios of ground truths. The performance metrics are the SIAP's Continuity, Ambiguity, Spuriousness, Positional accuracy, Velocity accuracy, Rate of track ID number changes, OSPA distance, and RMSE. Ten scenarios with different ground truths were used to test the six trackers. The tracking techniques showed variations in performance quality when all were tested under similar environmental conditions with some superiority in many cases for fusion-based techniques. This agrees with common sense but the paper has proven that with Monte Carlo simulations based on the 10 different scenarios. The work here is a baseline for future work that will use machine learning techniques to adapt the gating threshold along with the track-to-track fusion weighting parameter in the context of the complex environment described here.

This paper delves into the potential of quantum radar, leveraging entangled photons for improved performance compared to classical radar. Quantum illumination offers advantages in noisy environments, lowering intercept probability, and enhancing detection. Critical aspects, including detection range impact, realistic scenarios, and engineering challenges are explored. Receiver architectures like OPA and PC demonstrate quantum advantage, while the theoretical FF-SFG receiver promises to achieve the upper bound quantum limit. Scenarios from short to medium-range detection reveal quantum radar advantages, but long-range detection remains challenging due to high-frequency attenuation. Further research and technological advancements are essential for practical quantum radar applications.

In the diverse field of process industry, a plethora of technical processes are leveraged. Among these, liquids are often involved, being stored, transported and processed in tanks and reactors. Tailored to such applications, this contribution seeks to introduce and evaluate a novel technique for condition monitoring (CM). Within this technique, radar systems are employed and their functionality is augmented, enabling not only precise and accurate level measurements of liquids, but also distinction between different process conditions (PCs). For this purpose, distinguishing quantitative features are extracted from range-Doppler radar measurements. Thereafter, a classification is performed applying methods from machine learning. The potential of our proposed technique has been experimentally evaluated with respect to commonly encountered PCs. A frequency-modulated continuous wave (FMCW) Doppler radar system, operating in the V-/W-band, has been utilized for the measurements. It is demonstrated that the selected PCs can be distinguished with almost 98% accuracy, by extreme gradient boosting (XGB) along with quantitative features such as the peak-to-average power ratio.

Non-contact vital sign monitoring is crucial for minimizing patient interference. One of the advantages is that the patient will not be affected by sensors attached to the body. In this publication, a new signal processing method for heartbeat extraction is presented, based on Hilbert Transform envelope analysis, which is extended by a convolutional method with Gaussian pulses. Also, a plausibilty check for the detection of heartbeats in time domain is presented. The method is applied on radar measurements recorded by a dedicated 24 GHz vital sign FMCW radar. The proposed radar system hardware consist of three separate modules: a 2TX / 4RX MIMO radar front-end, a filtering-amplification module and a data acquisition module for the data transfer. All parts are developed in the Laboratory of Applied Radar and Optical Systems (LaROS) at the Trier University of Applied Sciences. The results are compared with an ECG system from GE Healthcare (CARESCAPE Monitor B650) as reference, confirming the effectiveness of the proposed methods.

Prior knowledge of subsurface layers is crucial in many applications, particularly infrastructural projects. Ground Penetrating radar (GPR) is a preferred measurement technique for investigating subsurface layers due to its non-destructive nature when probing the ground. However, interpreting GPR data is not trivial and requires the experience of the user. In this paper, the possibility of using one-dimensional Convolutional Neural Networks (1D CNNs) is investigated to estimate the thickness of up to two different subsurface layers with different electromagnetic characteristics. For this purpose, the network is trained on a synthetically generated stepped-frequency GPR Ascan dataset. The predicted thickness results using the trained 1D CNN showed good accuracy with a relative error of 2.6 % and 9.2 % for the first and second layers, respectively.

a multi-static radar system has an RF illuminator, which may be detectable by a third-party system, and one or more receivers that provide detection and geolocation of targets discreetly. Such an airborne system also allows mobility and long-range detection of low-altitude targets. The system discussed here is cooperative: the waveforms used by the system are knowledgeable by all the nodes of the system. We do not use opportunistic transmissions unlike PCL systems. As this system is likely to operate in adverse conditions, it must be autonomous, in particular it do not systematically rely for its synchronization on signals like those from GNSS, which may be unusable (absent, jammed or spoofed). This paper discusses three main challenges to overcome for making such system efficiently operating: -the synchronization of the oscillators, -that of the waveforms as well as the multiple beams forming at reception allowing the wide area search function and tracking.

Passive radar is a radar that does not emit signals but uses other sources of illumination. To determine the position of an object in a passive radar, distance measurements from at least three transmitter-receiver pairs are needed. The paper presents an adaptation of the maximum likelihood estimator to determine the position of an object based on multiple (three or more) bistatic or DToA measurements. The estimation quality factor was introduced. Stability of the numerical solution was analyzed.

In this study, we introduce a novel approach for object localization and tracking in passive radar systems, emphasizing the direct utilization of plots without the intermediate step of bistatic tracking filter application. This methodology aims to enhance the probability of early object detection, particularly in scenarios characterized by low Signal-to-Noise Ratio (SNR) levels. The paper delves into the implications of this method on the probability of object detection and the likelihood of false track generation. Through comprehensive simulations, we demonstrate that the proposed technique improves the detection probability in challenging environments and maintains a manageable rate of false tracks.

This paper presents an implementation of helicopter detection functionality in a multi-band passive radar system. The effectiveness of helicopter detection was examined based on the Coherent Processing Interval (CPI) and the radar's operating band, including FM radio, DVB-T2 television, and GSM network frequencies.

With the emergence of drones in many real-life applications, detecting and recognizing different flying objects became necessary. 2D ISAR imaging of flying objects helps recognize the various objects in the air. 3D ISAR imaging helps to further enhance the identification of the flying object. Interferometry introduces the capability to reconstruct 3D ISAR images by resolving the height along the baseline. In this paper, we apply sparse recovery techniques to real data of an in-air rotating drone to first form 2D ISAR images from multi-channels. Interferometry is then used to reconstruct the final 3D ISAR image.

Multi-dimensional synthetic aperture radar (SAR) imaging includes different approaches to get more information about a target, because the reflectivity of objects in a SAR image strongly depends e.g. on the radar frequency, polarization, and viewing angle. In this paper we focus on the analysis of multi-aspect SAR, where a scene is imaged from multiple aspect angles. Objects appear very different in SAR images with a data collection from different directions. The benefits but also the challenges of multi-aspect SAR are addressed using two different objects, a church and a basalt quarry, as an example.

This paper presents the results of a project focused on applying 3D Inverse Synthetic Aperture Radar (ISAR) imaging utilizing an FMCW X-band radar system. By employing the Polar Format Algorithm (PFA) for image processing, we have successfully demonstrated the system's ability to detect and identify various moving objects with high precision. Our findings underscore the practical utility of 3D ISAR technology in real-world scenarios, showcasing its potential to contribute significantly to advancements in surveillance and reconnaissance applications. While not introducing new imaging techniques, this study emphasizes the robustness and reliability of existing methodologies in processing and analyzing real-world data. The results highlighted in this paper affirm the contemporary technology's capacity to meet the challenges posed by dynamic and complex environments.

In this paper we present multi-dimensional SAR measurements performed with the Fraunhofer FHR MIRANDA-94 system. MIRANDA-94 is a beam-stabilized multichannel frequency modulated continuous wave (FMCW) radar with up to 3 GHz radar bandwidth at 94 GHz center frequency with a dual polarized receive antenna. In this paper we focus on high resolution multi-aspect and multi-polarization data acquired on linear and circular trajectories.

The SCA instrument is a C-band wind scatterometer, which forms part of the EUMETSAT Polar System Second Generation (EPS-SG) mission. Fully space qualified in December 2022, in January 2023 it has been delivered for integration on one of the two MetOp-SG satellites. The paper presents an overview on the SCA Instrument space qualification results, the thereof predicted in-orbit mission performance and ongoing satellite test results.

The paper presents the results of experimental investigations on the capabilities of detecting very-long-distance space objects moving in Low-Earth Orbit (LEO) based on bistatic measurements using the antenna array of a LOFAR (LOw-Frequency ARray) radio telescope and a non-cooperative radar illuminator operating in the VHF band. In this system, the signal transmitted by the non-cooperating radar is recorded using a relatively simple reference signal receiver located near the illuminator. The sensitive antenna array of the LOFAR radio telescope enables the reception of weak echo signals reflected from space objects orbiting in LEO, even those located very far from the illuminator and receiver in the bistatic sense. The detection of very distant and high-speed objects is made possible through the utilization of a dedicated object motion compensation method.

The paper presents the results of bistatic radar measurements devoted to the passive observation of Starlink satellites using a LOFAR (LOw-Frequency ARray) radio telescope. As the illuminator of opportunity in the analyzed passive radar system, a digital radio transmitter was employed. The presented idea allows for passive detection and monitoring of small satellites moving in LEO (Low-Earth Orbit) in the selected part of outer space.

Digital Video Broadcasting satellites (DVB-S and DVB-S2) present a high potential for passive radar due to their continuous illumination, transmission bandwidth and geostationary orbit. Their viability as an Illumination source for passive coherent location is already confirmed in the radar literature. In this paper, the use of polarimetry diversity in the surveillance channel of a DVB-S2 based passive radar is proposed to improve the detection performances of a single polarization DVB-S2 based passive radar. The designed signal processing scheme considers the combination of one single polarization reference channel and dual-linear polarization surveillance ones exploiting the depolarization effects on the target's scattered signal. A measurement campaign was carried out to analyse the advantage of the proposed processing scheme exploiting polarimetry diversity in the surveillance acquisition channel. The satellite version of the passive radar demonstrator IDEPAR from the University of Alcala was adapted to allow the acquisition of two linear polarizations in the surveillance channels. The radar demonstrator was deployed in a semi-urban scenario where a cooperative vehicle with a GPS recorder was used as a cooperative target for validation purposes. The detection outputs concerning the use of polarimetry based radar processing were compared with the single polarization case. Results show an improvement in the detector performance when polarimetry diversity is applied. The proposed processing approach reduced the false alarm rate while slightly increasing the detection probability in comparison with the best case of single polarization radar processing.

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Reverse forward scatter radar (RFSR) is a novel sensor which features a monostatic radar (MR) that illuminates the target against a background reflector. The crucial distinction from any other MR is that the forward scattering (FS) effect is exploited to measure the target using its forward scatter cross section, rather than the monostatic radar cross section (RCS). The first RFSR experimental measurements are shown with verification that the measured amplitude matches the expected values set by previous work on the theoretical power budget. Finally, the application of RFSR to stealth target detection is validated by showing the RFSR signature of a low RCS foam target is the same as that of a relatively higher RCS aluminum (Al) foil target of the same shape and size.

Reverse forward scatter radar (RFSR) is a monostatic radar that uses a background reflector to measure the forward scattered signals from a target. A spatially distributed reflector is used in the background for the first time to record the RFSR signature of a target. The results experimentally verify previous theoretical work by matching a measured and simulated signature. The ability of RFSR to measure stealth targets against a spatially distributed background reflector is demonstrated by showing that the RFSR signatures of two different targets are identical. The targets have the same shape and size but significantly differ in the backscatter radar cross section (RCS).

The continuous wave noise radar detection range is limited by the dynamic range of the receiver, which has to handle both long-range weak echoes and strong Tx-Rx signal leakage and strong echoes of ground clutter. One possibility to overcome this problem is to apply interrupted illumination, similar to the pulse radar case, but with duty factor around 50%. For far targets, the echo is received in the time when there is no transmission and no saturation occurs. For close range echoes saturation can still be present as return power is high, but the time of such problem is limited to short time after emission - depending of the product of light speed and range to the clutter. To avoid saturation at reception, the transmitted signal can be appropriately modulated in amplitude to achieve both full detection range without blind zone and linear reception within available dynamic range

During range calibration measurements of Noise Radar, a periodic structure in the Power Spectral Density of the radar receiver has been detected. We showed that this effect is due to summation of the radar returns and transmit/receive antenna leakage signals when a reflector is placed in the near zone, but beyond the coherence length of the transmitted noise signal. Theoretical consideration of the effect and comparison of the theoretical results with the experimental ones are presented.

The presentation will show the concept of a deployable multi-band passive/active radar network. The results of passive radar systems operating on their own, as well as in cooperation with active radars, will be shown, and the selected results obtained during the NATO STO APART-GAS (Active Passive Radar Trials - Ground-based, Airborne, Sea-borne) trials will be discussed. Additionally, the future applications of passive radar will be presented, including the new frontiers in modern passive radars relating to passive radar using new wideband illuminators of opportunity, such as WiFi, 5G/6G, DVB-S and STARLINK, and the required signal processing techniques. Finally, the talk will be summarized, showing potential ways to develop modern passive radars.

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