A sparse high-gain multifaceted circularly polarized antenna array based on partially reflecting surfaces (PRSs) is designed. Circular polarization is obtained by implementing the sequential phase rotation method at the source antenna level. Beamforming is implemented using phase compensation combined with amplitude weighting proportional to the radiated intensity of the given facet in the targeted direction, following the maximum ratio transmission concept. The radiation pattern is scanned across the angular region specified by the angular gap between adjacent facets. The obtained beamformed result shows a maximum gain fluctuation smaller than 0.5 dB across the scanned sector, together with a sidelobe suppression of 10.27 dB, and the obtained embedded element pattern exhibits a flat top.

A reconfigurable multiphase (MP) modulator is presented that avoids continuous generation and distribution of MP clocks by reconstructing switching waveforms from a memory-stored wavetable using an event-driven pulse generator. Reconfiguration is achieved by updating the wavetable, enabling changes in phase count (e.g., 8–16 phases) and duty cycle to tune spectral performance without modifying the pulse-generator core. A waveform-level proof-of-concept transmitter chain with a commercially available RF amplifier is demonstrated at carrier frequencies of 0.9, 2.4, 3.7, and 6 GHz. Orthogonal frequency-division multiplexing signals with bandwidths up to $500\,\mathrm{MHz}$ are used. In 8-phase, ${50}\%$ duty cycle operation, the measured out-of-band and in-band linearity achieves ${-48.3}\,\mathrm{dBc}$ adjacent-channel leakage ratio (ACLR) with ${1.56}\%$ error vector magnitude (EVM). Scaling from 8 to 16 phases via wavetable updates increases delivered output power by up to ${1.61}\,\mathrm{dB}$ while maintaining comparable ACLR and EVM. In 6-phase, ${33}\%$ duty cycle operation, the measured second- and third-harmonic rejection is approximately ${42}\,\mathrm{dBc}$ and ${45}\,\mathrm{dBc}$, respectively. These results validate the proposed architecture at the waveform level and motivate future integrated implementations with reconfigurable phase count and duty cycle.

This paper presents a differential split-ring resonator sensor, designed for the analysis of small volumes around 20 µl of liquid. One resonator is filled with a reference liquid while the other contains the liquid under test. Although the differential configuration reduces the influence of environmental parameters, it can lead to resonance overlap when the dielectric properties of the two liquids are close to each other. To overcome this limitation, a post-processing method based on Lorentzian fitting is used to accurately extract resonance parameters such as frequency and width, even when the resonances strongly overlap. The method is validated through experiments with water–ethanol mixtures of different concentrations. This shows excellent agreement between measured and calculated values. Eigenmode simulations are also performed to analyze field distributions, providing additional insight into resonance behavior. The proposed approach offers a reliable and general methodology for the analysis of differential resonant sensors.

With advances in deep learning for signal recovery based on sparse representation, this paper proposes two efficient sparse recovery (SR) networks to solve the target detection problem and generate range-Doppler maps in orthogonal frequency division multiplexing-based passive radar systems. First, by unfolding the alternating direction method of multipliers (ADMM) into a deep network with learnable parameters, a deep unfolding SR-ADMM-Net is developed, which avoids manual parameter configuration and achieves superior performance to ADMM. However, SR-ADMM-Net integrates sparsity prior information into the sparse recovery task via regularization but access only partial data domain knowledge. Therefore, this work proposes another method leveraging generative priors, which is derived from the least squares generative adversarial network (LSGAN) framework and termed SR-LSGAN. Generative priors can capture complex structural features of clutter and target signals, but their effectiveness depends on the solution space of the pre-trained generator. SR-LSGAN leverages prior distributions from the generative model and extends the solution space by dynamically fine-tuning parameters through gradient descent and internal learning, thereby improving recovery accuracy and target detection performance. Experiments on simulated and measured data demonstrate the generalizability and effectiveness of the proposed networks.

A microstrip low-pass filter with sharp roll-off and excellent suppression in both the near- and far-stopbands is proposed. The design incorporates a stepped-impedance hairpin-type resonator (SIHTR) along with a pair of asymmetric T-shaped resonators (TSRs). While the SIHTR offers a tunable 3 dB cutoff frequency and roll-off rate (ROR), its near-stopband suppression degrades at higher ROR values. To address this limitation and further extend the stopband bandwidth, two TSRs with distinct resonant frequencies are positioned at the input and output ports. By fixing their resonant frequencies and fine-tuning their stopband characteristics, the overall suppression bandwidth and stopband attenuation are significantly enhanced. The proposed filter features a compact layout, high selectivity, a wide stopband, and excellent out-of-band suppression performance. Measured results demonstrate an insertion loss of less than 1 dB and a return loss of greater than 15.1 dB in the passband from DC to 7.5 GHz. The 3 dB cutoff frequency is 8.23 GHz, and the transition band is 34.58 dB/GHz from -3dB to -40dB. In the stopband, attenuation exceeds 31.5 dB across the frequency range from 9.17 GHz to 40 GHz.

With the increasing level of wearable technologies, being intertwined with 5G networks, the necessity of high-speed and wideband communication solutions has gained top priority. The ultra-wideband technology presents a possible avenue for fulfilling these requirements. Following this drive, the proposed work establishes an ultra-wideband antenna system that is explicitly developed and validated to be used in 5G wearables. The designed antenna incorporates a dual-element multiple-input and multiple-output antenna featuring a stepped triangular-shaped radiator, evolved from an initial rectangular-shaped geometry. This transformation enables dual resonances at 4.7 and 7.9 GHz, covering a wide spectrum of 4.0–10.2 GHz. Furthermore, the suggested antenna demonstrates a minimum inter-element isolation exceeding 21.2 dB with a peak gain of 3.15 dBi. The multiple-input multiple-output diversity parameters have been investigated and observed to be within the acceptable limits, while the effectiveness for body-worn applications is further evaluated by analyzing its conformal performance and safety compliance, demonstrating average SAR values of 1.12 and 0.89 W/kg for 1g of tissue mass at 4.7 and 7.9 GHz, respectively. Finally, the antenna is fabricated, and its performance is validated through experimental measurements.

This work proposes a novel crossover cavity with high isolation and power handling capability. It consists of a one-pole Substrate Integrated Waveguide (SIW) circular resonator that excites two decoupled evanescent modes at the same resonant frequency. The proposed structure deploys two substrates acting as one evanescent-mode circular cavity. The electric fields of the evanescent modes are confined in the secondary substrate. Meanwhile, most of their magnetic fields exist in the main substrate. Each semicircular post is loaded by a capacitive load ($C_{1}$) in the secondary substrate, defining the resonant frequencies of the excited modes. Moreover, the isolation between channels is controlled through capacitive slots in the top metal layer of the main substrate. Consequently, the resonant frequency of the proposed crossover cavity and the isolation between its channels are independently tuned. The proposed SIW crossover cavity is implemented at 8.7 GHz with a size of (0.65$\lambda_{g}\times $0.65$\lambda_{g}$). A high-power handling capability of 44.7 dBm is measured. Also, 1.7 dB and 64 dB levels of insertion loss and isolation are measured, respectively. Furthermore, a 50-dB isolation bandwidth of 739 MHz is achieved. The scalability of the one-pole crossover cavity to a second-order transfer function has been demonstrated in a simulated two-channel crossover configuration.

The rapid advancement of the miniaturization techniques for high-frequency transceivers, radars, and communication systems operating in the D-band (110–170 GHz) has positioned circular dielectric waveguides (CDWGs) as a promising transmission-line alternative. Yet, their potential has not been fully exploited. This work fills this gap by introducing novel, compact CDWG-fed lens antenna solutions that deliver excellent gain and impedance matching performance. A low-loss, low-cost, and flexible CDWG made of low-density polyethylene is used to excite dielectric lens antennas of various sizes, contours, and materials, enabling a systematic evaluation of the impact of lens geometry on antenna performance. Through detailed electromagnetic simulations and experimental validations, lenses of different sizes and contours are designed. The proposed CDWG-lens configuration achieves measured broadband matching better than 17 dB and stable high gain across 115–130 GHz. Measured gains of 21–23 dBi for lenses with diameter of 10.6 mm and gain factor of 27–28 dBi for lenses with diameter of 20 mm confirm the high aperture efficiency and novelty of this approach. A strong agreement between the simulation and the measurement results is also observed. These compact and efficient lens antennas combined with the advantages of CDWG feed, can be integrated as a part of advanced system applications in the D-band frequency range like radar sensing and communications.

This paper presents a novel, independently controllable dual-polarized reconfigurable intelligent surface (RIS) unit cell for 6G upper mid-band ($7.125$–$24.25\,\mathrm{GHz}$) applications. The proposed unit cell is based on the diagonal placement of mutually orthogonal tunable radiators (loaded with varactor diodes) alongside static dual-polarized radiators. Full-wave electromagnetic simulations of the unit cell demonstrate a phase shift range of $270^{\circ}$, a maximum reflection loss of $4.5\,\mathrm{dB}$, and $61\,\mathrm{dB}$ cross-polarization isolation (XPI) within a $400\,\mathrm{MHz}$ frequency range centered at $15\,\mathrm{GHz}$. Furthermore, full-wave simulations of a $16 \times 16$ RIS panel were conducted for various reflection angles under both TE- and TM-polarized illuminations. The results demonstrate a wide-angle beam-steering capability of $\pm60^\circ$, with a maximum beam-pointing error of only $1.7^{\circ}$. The proposed RIS also exhibits accurate and stable reflection control under wide-angle excitation. A $3 \times 3$ prototype was fabricated to validate the unit cell’s performance. Measurement results agree with the simulations, yielding a $270^{\circ}$ phase shift, approximately $7\,\mathrm{dB}$ reflection loss, and $24\,\mathrm{dB}$ XPI. The proposed RIS is a promising candidate for future 6G communication systems.

This paper proposes an electronically controlled reconfigurable scanned array that uses movable short phase shifters suitable for 6G applications. Excellent performance is demonstrated by the passive electronically scanned array (PESA) operating in the centimeter-wave frequency region (13–17 GHz). Four digitally controlled variable reflect-type phase shifters, each built with a $90^\circ$ hybrid coupler with a movable short circuit, are integrated with a $ 2 \times 2$ horn antenna array. The assembly also has E–H feeding networks, which help the antenna array receive a uniform signal distribution. Outstanding performance is demonstrated and verified by time and frequency domain simulation results of the full PESA, which show continuous main-lobe scanning in the azimuth and elevation planes. Over the operating bandwidth, the proposed PESA maintains a steady gain of $14 \pm 2$ dBi while achieving a matching level below $-$12 dB.

Medical microwave imaging (MMWI) is emerging as a promising noninvasive diagnostic modality, offering a safe, portable, and cost-effective alternative to conventional imaging methods. Despite its potential, MMWI poses significant challenges due to the ill-posed and nonlinear nature of the underlying inverse scattering problem. Two main strategies are typically adopted: qualitative imaging, which yields rapid but approximate reconstructions, and quantitative imaging, which aims to recover the full permittivity distribution of tissues. Both approaches substantially benefit from accurate patient-specific background models that enhance reliability and reduce computational complexity. Building upon preliminary results presented at EuCAP 2025, this work advances the development of patient-specific head models for quantitative brain imaging. The study employs anatomically conformal basis functions and extends the model to include cerebrospinal fluid, which represents a strong scatterer with markedly distinct dielectric properties. The proposed framework improves reconstruction accuracy and convergence efficiency, thereby contributing to the advancement of quantitative MMWI toward practical clinical applications.

This paper presents the design and experimental validation of a compact corrugated double-tapered slot Vivaldi antenna (DTSVA) for ultra-wideband (UWB) applications. The proposed antenna provides efficient impedance matching over a wide frequency range of 1–20 GHz. To suppress electromagnetic interference from coexisting narrowband systems, triple band-notched characteristics are realized using spatially distributed resonant elements, including a complementary split-ring resonator (CSRR) and U-shaped slots etched beneath different sections of the feed network, enabling effective rejection of WiMAX (3.3–3.8 GHz), WLAN (5.15–5.85 GHz), and X-band uplink (7.9–8.4 GHz) signals. To enhance forward radiation without increasing the antenna size, corrugated edges and an anisotropic zero-index metamaterial (AZIM) unit cell are integrated within the tapered slot region. Consequently, the proposed antenna achieves a maximum peak realized gain of 12.5 dBi, corresponding to an improvement of up to 3.8 dBi compared to the reference DTSVA. Simulated and measured results show good agreement in terms of impedance bandwidth, radiation characteristics, realized gain, and group delay. Owing to its compact size, enhanced gain, stable time-domain performance, and effective interference suppression, the proposed antenna is well suited for portable indoor and outdoor UWB applications, including imaging, radar sensing, and material characterization.

This paper introduces a methodology for detecting and classifying railway infrastructure elements using ground-penetrating radar (GPR). Seven trips, covering $57.4\,$km across a German track network were recorded. The network includes ballasted tracks, switches, bridges with dominant metal elements, and overpasses. GPR data from a multi-channel sensor array is transformed through a preprocessing pipeline to generate spatial B-scans. Statistical and structural features, including energy, depth, and skewness, are extracted via an overlapping sliding window. The detection algorithm operates as a streaming process, combining correlation-based pattern matching with feature-based thresholds in a state-machine architecture. The evaluation results demonstrate overall good performance for infrastructure detection and classification ($98$–$100\%$), with only minor misclassifications occurring for switch orientation estimation in scenarios involving closely spaced or physically interconnected switches ($82$–$100\%$).

This paper investigates the use of large Reconfigurable Intelligent Surfaces (RISs), also known as “Smart Skins,” to improve outdoor-to-indoor millimeter-wave (mmWave) propagation, taking advantage of ventilation holes commonly found – or easily implemented – in European buildings. By using a transmissive, focusing RIS, the signal can be concentrated and routed through the opening, enhancing signal penetration into the indoor space even in modern, highly insulated buildings that particularly hinder signal penetration. Using Ray Tracing simulations, we compare scenarios with and without RIS at 29 GHz, demonstrating significant indoor signal coverage improvements in the first case. The study highlights the use of RIS – or Smart-Skins – as a cost-effective solution to address the challenges of mmWave propagation in modern building designs.

A novel family of $Ku$-band highly selective multi-band bandpass filters (BPFs) realized using groove-gap-waveguide (GGW) technology is presented. The conceived multi-band BPF structures are derived from a quasi-elliptic-type single-band prototype by applying a split-type single-to-multi-band frequency transformation. The baseline single-band prototype incorporates extracted GGW-rectangular-cavity sections at both the input and output accesses, which are preserved in the multi-band extension as multi-cavity tails. These extracted cavities enable the generation of multiple stopband transmission zeros (TZs) to obtain steep-attenuation characteristics in fully inductive-coupling filter structures without the need for cross-coupling mechanisms. Theoretical design examples of fourth-order dual-band and sixth-order triple-band filtering responses are developed using the coupling-routing-diagram formalism. These examples demonstrate the versatility of the proposed multi-band BPF approach in terms of bandwidths and center frequencies for passbands, spectral symmetry or asymmetry, and out-of-band TZ placement. For experimental-validation purposes, a proof-of-concept GGW dual-band BPF prototype exhibiting fourth-order passbands centered at 14 and 14.4 GHz and five stopband TZs is designed, manufactured, and measured. A compact two-layer vertically stacked GGW configuration is adopted for its physical implementation, confirming the practical feasibility of the proposed architecture. In addition, electromagnetic-simulation-based sensitivity analyses are performed to assess fabrication robustness, and a quantitative comparison with prior-art designs is provided to evaluate the RF-performance merits of the developed Ku band GGW dual-band BPF.

This work proposes a band-switchable electrically small antenna (ESA) system for a wearable health monitoring device. The system operates at multiple 5G-NR bands (875–934 MHz and 1.72–2.2 GHz) using a switchable configuration. The antenna consists of multi-resonant shorted strips that have been miniaturized to fit in meandered form into an area of 63.2$\times$25 mm$^2$ (0.19$\times$0.08$\lambda^2$) available in the intended health monitoring device. To enable operation at two distinct modes, the antenna feedline has been integrated with a switch, which is then matched using lumped matching components. Results indicate that the ESA system operates at 875–900 MHz in Configuration 1, and at 898–934 MHz and at 1.72–2.2 GHz in Configuration 2. The device has been fabricated and integrated into a compact 3D printed casing prior to experimental evaluations. In addition to studying the switchable reflection and radiation performance, the ESA is also evaluated in the presence of a human body phantom. Simulated specific absorption rate levels are less than 0.47 W/kg averaged over 1 g of tissue, which complies with international standards.

This paper presents the design, optimization, fabrication, and measurement of three RF-to-DC rectifiers operating at 3.5 GHz for wireless power transfer and RF energy harvesting applications. A low-power rectifier achieves a peak efficiency of 50.5% at -2 dBm, while a high-power rectifier reaches 61.2% at 15 dBm. To extend the operating range, a wide-range rectifier based on a passive dynamic sub-rectifier selection architecture is proposed. The developed system achieves a maximum efficiency of 54.7% at 16 dBm and maintains over 20% efficiency across a 41 dB input power range. Experimental results validate the proposed designs and show good agreement with simulations.

Additive manufacturing is an enabling technology for a wide range of applications, particularly within the domain of electromagnetism, where components and antennas can benefit from its use. The objective of this study is to design antennas with different effective permittivities using only a small number of dielectric materials that are compatible with additive manufacturing. A formalism based on the construction of macrocrystalline cells employing Bravais lattices is utilized to accurately analyze the homogeneity and properties of the materials. This formalism is then used to synthesize a specific effective permittivity with polymers or ceramics. Following experimental validation of the method, it was applied to the design of dielectric resonator antennas, which were then validated using measurements in C-band. This paper presents an original construction of a multipermittivity material based on the formalism outlined above. This development offers interesting possibilities for antenna designers.

This study presents the development of a 3D-printed, wideband, dual-polarized magneto-electric dipole antenna. The proposed antenna demonstrates exceptional cross-polarization isolation (XPI) between its two mutually orthogonal RF ports, achieved through innovative feeding probes, specifically an inverted $\Gamma$-shape and a conventional $\Gamma$-shape probe. The analysis reveals that misalignment between probes can impair XPI; this phenomenon is systematically examined through electromagnetic full-wave simulations. A practical remedy is provided using four plastic rods strategically positioned through the probes and posts. Measurements indicate that XPI exceeds 50 dB across the common operating frequency range of 3.05–4.13 GHz (30%). The maximum realized gain is approximately 7.9 dBi, with a nearly flat response and stable radiation patterns across both ports throughout the bandwidth. The proposed antenna offers a cost-effective, 3D-printed design, wideband radiation performance, and exceptional port-to-port isolation, demonstrating significant potential for full-duplex wireless communication and ICAS applications.