This paper presents the design and evaluation of reflectarray antennas at spherical surfaces aimed at achieving an optimal compromise between electrical performance and mechanical deployability for satellite antenna solutions based on offset reflector configurations. By implementing printed reflectarray elements on a spherical surface, the phase-shifting elements mitigate spherical aberration, leading to enhanced focusing capabilities comparable to those of parabolic reflectors. The spherical geometry inherently simplifies the folding mechanism due to the rotational symmetry of the reflecting surface and minimizes the differential spatial phase delay, improving the reflectarray in-band performance. Simulation results demonstrate that large-aperture spherical reflectarrays can replicate the gain and beam quality of parabolic reflectors with smoother phase distributions than flat or multifaceted reflectarrays. The integration of spherical reflectarrays in dual-antenna configurations is evaluated to realize compact and efficient antenna systems for next-generation satellites.

This research presents the design and development of a microwave sensor capable of detecting and distinguishing hydroxylated organic compounds (HOCs), namely water, methanol, ethanol, and propanol. The work analyzes the physical mechanisms that govern the sensitivity and detectability of these liquids in the microwave range. Differences in sensor response are linked to variations in molecular characteristics such as dipole moment, microwave absorption, and refractive index. Unlike approaches that rely solely on experimentation, this study connects microwave behavior to fundamental molecular properties, enabling a predictive, physics-based understanding of HOC detection. Molecular polarization and relaxation models were combined with experimental observations to explain how these compounds interact with microwave fields. A metamaterial-based sensing cell was designed, simulated, and experimentally validated. Results demonstrate that the sensor effectively identifies hydroxyl compounds with high sensitivity. Water produced the highest resonance-frequency shift (0.76 GHz), followed by methanol (0.7 GHz), while ethanol and propanol showed similar shifts around 0.35–0.37 GHz. Propanol achieved a quality factor of 10.82 in the 12–17 GHz range. The sensor also reached a frequency detection resolution of 6.75 MHz and showed strong amplitude sensitivity, highest for water at 10.66 dB.

This study presents an innovative method for in situ measurements of electrical conductivity at microwave frequencies using a dielectric resonator (DR)-based probe. The DR, excited in the transverse electric mode with azimuthal index 0, radial index 1, and an open (non-integer) axial field variation denoted by δ (TE01δ mode) by a ridged waveguide, interacts with metallic layers as small as 5 × 5 mm2 on a dielectric substrate, enabling precise conductivity measurements through reflection coefficient analysis and electromagnetic simulations. Validation is performed by comparing the probe’s conductivity extraction results at 13.28 GHz with a conventional resonant cavity method at 10 GHz, demonstrating strong agreement. The used samples are therefore much smaller than what other comparable methods would require. The method is further applied to additively manufactured metallic deposits produced via a micro-dispensing technique, providing insights into their high-frequency (HF) conductivity and the effects of surface roughness. Additionally, a second-generation contact-based probe is developed to extend the characterization capabilities to larger samples and perform HF surface conductivity mapping. This advancement enables localized evaluations of surface properties and correlations with roughness, offering a valuable tool for optimizing additively manufactured components for HF applications.

This paper presents an actively controllable nonreciprocal metasurface based on a ferrite–patch structure with PIN diodes for dynamic control. Two activation methods are investigated: (a) phase control, which enables a 30° transmission-phase shift while maintaining nonreciprocal behavior, and (b) ON–OFF control, which switches the response by altering the propagation path. The phase-control metasurface is analyzed using transmission-line theory, full-wave simulation, and experiments, showing good agreement across methods. The ON–OFF design is optimized to suppress bidirectional transmission when ON. Experimental results confirm strong nonreciprocity, though slight frequency shifts arise from FR4 variability, and a back-fitted simulation improves consistency. The proposed dual-control framework provides a compact and low-cost approach to reconfigurable nonreciprocal surfaces that retain the use of permanent magnets for ferrite bias and are applicable to microwave wireless systems, including adaptive isolation, interference control, and tunable shielding. The results demonstrate the feasibility of compact, reconfigurable nonreciprocal metasurfaces using simple biasing circuits and offer design insights for frequency-stable implementations.

This paper presents a dual-band reflectarray antenna based on a 1-bit hybrid active/passive metasurface, achieving independent four-beam radiation at frequencies of 5.8 and 9.7 GHz. The proposed unit cell integrates an active double-split square ring with PIN diodes for 180° phase switching at 5.8 GHz, and a passive cross-shaped patch for 180° phase control at 9.7 GHz. A chessboard-like coding arrangement enables independent beam steering at both frequencies. Experimental results from a fabricated 15 × 15 metasurface prototype show stable four-beam operation, with measured steering angles of 19° and 12.1°, and 3-dB beamwidths of 10.2° and 11.5° at 5.8 and 9.7 GHz, respectively, validating good agreement with simulations. The proposed metasurface demonstrates significant promise for applications in multiband radar and communication systems requiring compact, low-profile, reconfigurable antennas.

A reinforcement learning (RL)-based automated antenna topology optimization method is proposed. The proposed framework can be divided into three phases, which are high-quality dataset construction, electromagnetic (EM) simulation acceleration, and RL-driven automated antenna topology optimization. Based on the high-quality dataset, a fully trained enhanced hybrid multilayer perceptron is proposed to replace time-consuming EM simulations. This approach allows the RL to acquire knowledge from the interaction between antenna topology and the environment quickly, reducing the optimization time cost caused by the large number of EM simulations. Additionally, two crucial components, topology bidirectional mapping strategy (TBM) and topology hierarchical analyzation strategy (THA), are introduced in this work to address the compatibility problems between ML and high-dimension antenna topology data. To verify the effectiveness of the proposed method, a microstrip patch antenna operating at 2.45 GHz is optimized. According to the measurement results, the antenna performance of gain and impedance bandwidth is improved greatly at the same time through the proposed method.

With the widespread application of smart antennas in 5G communication and radar detection, adaptive beamforming technology based on deep learning has become a research focus for improving the anti-interference performance of antenna arrays due to its powerful nonlinear modeling capability. It can transform the beamforming problem into a neural network regression problem, enabling the model to rapidly output an approximately optimal beamforming weight vector without prior information. Aiming at the issues of poor adaptability to dynamic interference and high computational complexity of traditional algorithms, this paper proposes IRDSNet, a novel adaptive beamforming algorithm based on Inception-ResNet-dual-pool Squeeze-and-Excitation Network (DP-SENet), to optimize the performance of uniform circular array antennas. IRDSNet integrates the Inception structure, depthwise separable convolution, and Ghost convolution to construct a multi-scale feature extraction module, enhancing the model’s feature extraction capabilities while maintaining a low parameter count. By introducing an improved DP-SENet, the model’s ability to focus on key features is enhanced, while the incorporation of residual modules optimizes feature transmission efficiency. Simulation results demonstrate that the IRDSNet algorithm achieves a null depth exceeding −90 dB at various interference angles, with an output Signal-to-Interference-plus-Noise Ratio (SINR) consistently above 23 dB and a short inference time, demonstrating excellent interference suppression performance.

This paper presents a highly isolated diplexer-antenna and a dual-band filtenna with high-frequency selectivity. The precise design procedure for the diplexer based on substrate-integrated waveguide technology is presented and effectively integrated with magnetoelectric dipole antenna/microstrip patch antennas to achieve a diplexer-antenna and dual-band filtenna. The proposed configuration enables the design and control of the filtering response of the channels individually. To verify the proposed method, a diplexer-antenna and a dual-band filtenna with operating frequencies of 26.5–27.5 and 28.5–29.5 GHz, a fourth-degree Chebyshev response, and two symmetric radiation nulls for each band are designed and simulated. Finally, the proposed dual-band filtenna is fabricated and measured. The measured peak realized gains for the lower and higher bands are 4 and 4.5 dBi, respectively. Besides, a high out-of-band suppression with a deep roll-off of better than 20 dBi is obtained.

In this paper, a dual concentric square-loop dual-polarized reconfigurable frequency selective surface with a high tuning ratio of 2.02 operating in the 1.53–3.10 GHz band is proposed. This high tuning ratio has been achieved by using four SMV1430-LF varactor diodes, which have been actuated using a simple biasing arrangement made of stubs and four metallic vias per unit-cell. The unit-cell has been rigorously analyzed, and an equivalent circuit (EC) model has been developed for the physical insight. The proposed EC model also demonstrates the reconfigurability of the unit-cell and thus predicts its behavior. The effect of the angular incidence of the impinging electromagnetic wave on the structure up to a 45º has been experimentally verified, which demonstrates its angular stability and polarization insensitive behavior. The structure may find applications in the electromagnetic spectrum’s L, S, and 2.45 GHz ISM bands.

The design of filters used in waveguides, which are crucial components of high-frequency communication systems, plays a significant role in improving system performance. In this study, the usage of metamaterials is first proposed, the SLA 3D printing method is used to design and fabricate CSRR meta-resonators-based bandpass waveguide filters (WGFs) with different filter orders for C-band (4-7.5 GHz), and simulated and measured filter performances are compared. Since the proposed novel WG structure is modular, it allows the design of C-band WGFs using different thicknesses of substrate materials. Also, the number of unit elements can be increased and any number of meta-resonators can be inserted to design filters of different orders ranging from 1 to 5. The electrical length of the WGF/WG structure can be changed according to the needs of the applications. The resulting WGFs demonstrated superior RF performance, being 50% lighter than comparable models found in the literature. Over the relevant frequency range, the filter exhibited return losses between 31-43 dB, insertion losses from 0.1 to 0.35 dB, FBW ranging from 12% to 16%, and quality factors between 6.23 and 8.28, depending on the filter order. The obtained experimental results align closely with the simulation predictions, confirming the effectiveness of the design.

This article examines the benefits of utilizing site and orbital diversity reception techniques at Ka- and Q-bands in South Eastern Europe, comparing their performance in Cyprus and Greece. The assessment relies on measured rainfall rate statistics, collected near the selected locations in both countries. The study compares and evaluates the performance of double and triple site and orbital diversity scenarios. The simulation outcome reveals that the adoption of double and triple site, or double and triple orbital diversity configurations leads to considerable enhancements in outage performance in both frequency bands. The delivered improvements are markedly significant when specifically 3-site and 3-orbit diversities are applied, especially at Q-band. However, the orbital diversity demonstrates inferior performance compared with site diversity. Notably, for satellite systems demanding extremely high levels of service continuity, the 3-site diversity approach proves highly effective at Ka- and Q-bands, accomplishing this without necessitating overly large fade margins. Comparing Cyprus and Greece, the latter demonstrates lower outage improvements due to the higher measured rainfall rates. Finally, for a dual orbital diversity scenario in Greece, measured experimental results are presented in terms of joint attenuation and compared with the theoretical model, exhibiting noticeable accuracy.

This paper presents a circularly polarized (CP) antenna employing both uniform and non-uniform metasurfaces to achieve wideband characteristics. The proposed antenna consists of a dual-feed CP antenna as the source element, a 4$\times$4 metasurface lattice as the superstrate, and a sequential feed network. Initially, the performance of the antenna is analyzed using a uniform metasurface. Subsequently, by adjusting the size of the inner unit cells, the uniform metasurface is transformed into a non-uniform configuration. The proposed design with a uniform metasurface achieves a $-$10 dB impedance bandwidth ranging from 5.21 to 6.47 GHz (21.57%) and a 3-dB axial ratio bandwidth from 3.96 to 6.67 GHz (50.9%). The use of a non-uniform metasurface significantly improves the overall antenna performance, achieving a $-$10 dB impedance bandwidth and 3-dB AR bandwidth of 4.98 to 7.45 GHz (40%) and 2 to 7.26 GHz (113%), respectively. The optimized design with a non-uniform metasurface is fabricated and tested. Overall size of the antenna is 40$\times$40$\times$3.4 mm$^3$ (0.72$\times$0.72$\times$0.062 $\lambda_{0}^3$), where $\lambda_{0}$ represents effective wavelength at an operating frequency of 5.5 GHz. The simulated and measured results of the proposed antenna are found to be in good agreement.

Dielectric lens antennas provide significant advantages for various radar-based applications. While an ellipsoidal geometry is often utilized due to its beneficial antenna characteristics and its point-like feed into the lens, its length and antenna reflections are drawbacks for some applications. In this work, we investigate the design of a Fresnel-based lens antenna to overcome these limitations. A quasioptical design is presented, highlighting its ability to reduce internal reflections of lens antennas. Additionally, the effects of the number of Fresnel steps and manufacturing tolerances are analyzed. Measurements validate the design and demonstrate the reduction of internal reflections by more than 13 dB, leading to an increased measurement range in a Tank Level Probing Radar scenario and a size and weight reduction of 41% and 34%, respectively.

This paper presents a multiple input multiple output (MIMO) system for sub-6 GHz using a two-port cylindrical dielectric resonator (CDR). This band is ideal for 5G applications, providing a balanced combination of coverage and capacity, as well as offering high data rates and low latency. The proposed MIMO is excited by an aperture-coupled feed structure composed of driven elements consisting of an elliptical-shaped step impedance transform line to enhance CDR coupling. Aperture coupling is used to excite the HEM11δ mode without the involvement of any hybrid mode. The purpose of the aperture coupling in the CDR antenna is to launch the HEM11δ mode, which is a magnetic dipole that provides a stable radiation pattern in the 3.2–3.7 GHz band, allowing for efficient transmission and reception of the data. Symmetrically oriented CDR and the presence of orthogonal fields provide good isolation, which can be further improved by the insertion of an asymmetric cross slot. The designed CDR-based MIMO antenna achieves excellent isolation of over 20 dB and demonstrates improved envelope correlation coefficient (ECC) values, resulting from low field correlation, across the entire frequency band of operation. Almost all the major diversity analysis was carried out for the desired sub-6 GHz band while maintaining a relatively compact size. Based on the measured results, it is confirmed that the proposed CDR-based MIMO antenna is appropriate for sub-6 GHz applications.

The design of a hexagonal six-ridged waveguide (H6RWG) phased array antenna (PAA) element featuring a wide scan angle matched slotted horn aperture is presented for Ka-band satellite downlink in low Earth orbit non-terrestrial network applications. The proposed PAA element is evaluated against an open-ended waveguide (OEWG) PAA element and achieves a very low active reflection coefficient (ARC) of less than -18 dB and a total antenna efficiency greater than 84% over a wide bandwidth from 17.3 to 20.2 GHz with a $\pm$ 50$^\circ$ scan range. Specifically, the aperture of the H6RWG was designed to limit the variations in ARC during scanning, thereby minimizing load pulling of integrated active devices, as demonstrated with a power amplifier (PA) in a co-simulation. As a result, the power-added efficiency, output power, and linearity of the PA remained stable over the bandwidth and scan range. Compared to the OEWG PAA, the co-polarized system efficiency and equivalent isotropic radiated power are improved for most scan angles within the bandwidth, especially at high scan angles.

This paper proposes and experimentally validates four origami-inspired reconfigurable waveguide antenna designs, including the vertical folded waveguide antenna, the tilted waveguide antenna, the bellowed tilted waveguide antenna, and the fan-fold horn antenna. Aimed at overcoming the inherent limitations of rigid waveguide, those designs use mechanical deformation to control electromagnetic performance. By leveraging simple folding mechanisms, those proposed structures can turn antenna’s key parameters such as operating frequency, beam direction, beamwidth, gain and beam shape without relying on active components or complex beamforming circuitry. All prototypes were handcrafted as proof-of-concepts and successfully demonstrated their targeted functionality, showing the great potential in applications that require occasional reconfiguration rather than rapid, continuous adjustment. These results also reveal how origami techniques can unlock new design freedom for compact, reconfigurable antennas for future communication and sensing system.

A low-profile dual-circularly polarized (CP) antenna array using spiral sequential rotation (SSR) technique is proposed. The array element consists of two stacked CP patches and a double-layer ceramic substrate with high dielectric constant. Dual CP radiations are accomplished by the slender rectangular structures on the radiators, which can excite two orthogonal characteristic modes. An extremely small size of 0.005λ3 (λ is the wavelength in free space for the low bands) and a wide 3-dB axial ratio beamwidth (ARBW) of 206° are achieved. Furthermore, the SSR technique is employed to achieve low cross-polarization level (XPL) within a large scanning angle. Prototype of a 6 × 6 array was fabricated and measured. Experimental results demonstrate that a wide 3-dB AR scanning angle of ± 55° is realized for LHCP as well as RHCP radiation. Additionally, low XPL less than −18.1 dB with gain fluctuation less than 4 dB are achieved over −55° ∼ + 55°. Meanwhile, the array has successfully passed the mechanical test and the thermal vacuum test (−90° ∼ + 90°). All the merits of dual-CP radiation, extremely low profile of 0.06λ, wide 3-dB AR scanning capability, and low XPL make our proposed dual-CP SSR antenna array be attractive candidate for satellite applications.

This paper provides a profound perspective on the neuronal property of radiofrequency (RF) power amplifiers (PAs). The nonlinearity of the PA is studied for the first time by solving differential equations in a bio-inspired neuromorphic model, i.e. Hodgkin–Huxley model, with Bayesian estimation. This study demonstrates that the nonlinearity of RF components is biomimicking and thus can enhance neuromorphic computing capacities of a communication network under the framework of a joint communication and computation (J2C) scheme. Overall, our work contributes to incorporating artificial intelligence (AI) and automation into the communication network, a key trend in 6G.

Proper management of mutual interference plays an important role in the successful simultaneous operation of automotive frequency-modulated continuous-wave (FMCW) radar sensors at different vehicles. Compared to traditional interference handling concepts such as detect-and-mitigate or detect-and-avoid, the detect-and-exploit paradigm turns the originally interfering signals into signals of interest and uses them to obtain information about the environment. Following this idea, a method that implements such an interference exploitation strategy in terms of joint passive spectral sensing and localization of surrounding objects is elaborated and presented in this work. In summary, the method consists of a dedicated radar operational mode and a corresponding signal processing chain including pre-processing, beam steering-based signal component separation, maximum likelihood (ML)–inspired signal parameter estimation, and joint direction of arrival (DoA)-time difference of arrival (TDoA) based object localization. The unique advantage of the presented concept compared to over-the-air synchronization (OTAS)-based solutions is that it can also deal with interferers that change their ramp parameters over time. The applicability of the concept is both theoretically analyzed as well as practically demonstrated by means of measurements in an anechoic chamber, where the position of the interferer and an additional object in the surrounding can be determined with an accuracy of a few centimeters.

Proximity feeding is the simplest technique to achieve wideband response in a microstrip antenna on a thicker substrate. However, the bandwidth is limited on a thinner substrate due to the capacitive impedance offered by the feeding strip. This paper presents wideband designs of proximity fed rectangular microstrip antennas loaded with printed open Ring shape or C-shape resonators, while using a thinner substrate. On substrate thickness of 0.053λg, the proposed design yields a bandwidth of 214 MHz (23.62%) with a broadside radiation pattern and peak gain of 8.0 dBi. Against the thicker substrate proximity fed design, a reduction of ∼ 0.03λg in thickness is obtained. With the obtained antenna characteristics, the proposed design is useful in 800–1000 MHz, GSM band applications.