The antenna characterization from planar near-field (NF) measurements is generally realized by using the classical NF to far-field transform technique of plane wave expansion (PWE). This approach imposes strong constraints on NF sampling. To overcome these limitations, an equivalent model of the antenna under test (AUT) is created based on a distribution of infinitesimal dipoles. A reduced-order model (ROM) of the problem is constructed to obtain a decomposition basis defining the radiated field. The powerful ability of the ROM in determining the number of points needed for accurate NF measurements is demonstrated. Also, efficient non-conventional sampling strategies are applied to the case of planar NF measurements and the influence of these distributions on the reduction of the number of samples is studied. The global analysis of our approach on simulated and measured NF data shows that only 20% of the total number of points are needed with respect to the classical PWE technique to achieve an accurate characterization.

One-bit coding metasurfaces combine two basic unit cells with out-of-phase responses. Their potential in achieving diffuse scattering has already been demonstrated. These metasurfaces can subsequently be applied to radar-signature control. This paper presents a theoretical analysis linking the scattered field to the autocorrelation of the code that encodes the metasurface. This analysis leads to a focus on Minimum Peak Sidelobes codes with autocorrelation characteristics similar to the unit impulse. Advances in other research areas have greatly enhanced the search for these kind of codes, making them directly usable for coding diffuse scattering metasurfaces. This approach is compared with existing codes, specifically examining how it performs against the optimal code found through exhaustive search in small-scale scenarios. Then, it is shown that this coding strategy facilitates the design of metasurfaces with any and large electrical sizes, achieving results comparable to those obtained through optimization-based approaches, at a significantly reduced computational workload.

This paper presents for the first time the implementation of an Si/SiGe heterojunction bipolar phototransistor (HPT) into an STMicroelectronics BiCMOS technology together with the development of hydrodynamical model that fits in a trustable manner the measured opto-microwave performance. The developed hydrodynamical model relies on a precise topology analysis of the HPT and an efficient optical absorption coefficient model. It is key to predict the optimization required for the HPT. Simulation results with responsivities of 0.92 A/W and bandwidth of 1.55 GHz are obtained at low $V_{\scriptsize{\text{CE}}}=2$ V and for small devices with $2 \times 2\,\unicode{x00B5} \text{m}^{2}$ optical window. Simulation results are used to identify the best horizontal geometry that maximizes the gain–bandwidth product of the HPT. The behavior of the photo-generated carriers in the active region of the device is investigated.

In this article, we discuss the behavioral modeling of the power amplifier (PA) for system-level simulations through its most advanced approach, named TPM model, based on a simplification of the Volterra series following the method of separation of the low and high frequency memory effects present in PA. The model, relying on frequency domain CW characterization of the PA, shows a limitation when applied to high-power radar applications, for which this article investigates an alternate solution based on time-domain pulsed RF characterization.

In this article, we present a simulation tool for modeling a quasi-optical bench for material characterization. The model uses a Gaussian beam expansion and tracking analysis, together with a modal analysis to enable a comparison of the simulated reflection and transmission S-parameters to the ones measured with a 4-port vector network analyzer. A Thru-Reflect-Line calibration is performed to de-embed the simulated S-parameters of a dielectric slab located between two lens antennas, showing good agreement with the analytical slab model used for experimental permittivity extraction.

In this paper, the design and optimization of a circularly polarized antenna based on two crossed dipoles in phase quadrature for Global Navigation Satellite System (GNSS) wide band application has been investigated. The proposed design is single fed and relies on parasitic structures to achieve wide band coverage on the GPS standard bands L1 (1559–1610 MHz) and L5 (1164–1189 MHz). Full-wave simulations have been used to compute the radiation properties and the impedance of the antenna. A prototype was manufactured, and good agreement has been observed between the simulated results and measurement for both radiation pattern and reflection coefficient.

The antenna achieves a −10 dB impedance bandwidth of $56.97\%$ covering the band 1164–1610 MHz, and an axial ratio that covers the L5 band ranging between 7 dB and 2.8 dB from 1.164 GHz to 1.3 GHz while maintaining a value below 2.7 dB across the entire L1 band. The antenna occupies a volume of $\,99\, \,\times\,99\, \times 50$ mm3. It has been tested in real conditions during the 23rd French National Microwave Days (JNM) student competition. A GNSS signal receiver has been connected to the antenna. The antenna has been evaluated based on the number of connections it could achieve over a duration of 30 s.

This paper presents the design, simulation, and real-world validation of a compact, dual-band, right-hand circularly polarized antenna for Global Navigation Satellite System (GNSS) applications. The antenna operates in the L1 (1575 MHz) and L5 (1176 MHz) bands, utilizing a stacked patch structure on low-cost FR4 substrates to achieve compactness and circular polarization. The design ensures axial ratio values below 3 dB, with peak gains of 2.59 dBi (L1) and -0.89 dBi (L5), while maintaining wide radiation coverage. Unlike many recent proposals based on Rogers substrates or complex geometries, our design focuses on cost-effectiveness and manufacturing simplicity. The prototype was validated using a Quectel LC29HAAMD GNSS receiver during the 2024 French National Microwaves Days (JNM), successfully acquiring over 40 satellites within 60 seconds in a real-world suburban environment. These results demonstrate the antenna’s suitability for space-constrained and low-cost GNSS platforms in the “New Space” era.

Photoconductive antennas (PCAs), known for their broad bandwidth, high data rates, and simple structure, are gaining significant attention in terahertz (THz) applications. Over the past decade, THz PCAs have been extensively researched, demonstrating diverse applications across multiple fields. This paper provides a comprehensive review of PCA theory and design, along with an in-depth analysis of their relative advantages. Additionally, various strategies for enhancing antenna efficiency are discussed, focusing on material selection and geometric design. This review aims to offer researchers a consolidated resource, presenting key insights into the challenges and advancements in PCA research.

In this paper, we demonstrate wideband orthogonal frequency division multiplexing (OFDM) at sub-mmW frequencies with full electronic data and carrier generation. We present the first stringent examination of OFDM-waveform design in a fully electronic experimental setup. Operating at 309 GHz center frequency and modulated channel bandwidths of 2 and 10 GHz, the performance of single-carrier waveforms is compared to OFDM signals with varying modulation formats and subcarrier settings. In addition to the investigation of the gross data rate, which is resulting in 20 Gbit/s for OFDM and 40 Gbit/s for single-carrier, we give one of the first demonstrations of joint communication and sensing with OFDM-signals at sub-mmW frequencies, as the distance between transmitter and receiver isdetermined by examination of the received signal.

A dual-band dual-polarized wearable antenna that applies to two different operating modes of wireless body area networks is proposed in this letter. The antenna radiates simultaneously in the ISM band at 2.45 and 5.8 GHz. It consists of a rigid button-like radiator and a flexible fabric radiator. At 2.45 GHz, an omnidirectional circularly polarized pattern is radiated by the flexible radiator, which is suitable for the on-body communication. At the same time, a linearly polarized broadside pattern for off-body communication is generated by button radiator at 5.8 GHz. The antenna has been validated in free space and human body environments. The impedance bandwidth at 2.45 and 5.8 GHz are 5% and 35%, and the gain is measured to be 0.15 and 5.95 dBi, respectively. Furthermore, the specific absorption rates are simulated. At 2.45 and 5.8 GHz, the results averaged over 1 g of body tissue are 0.128 and 0.055 W/kg. The maximum value at both bands is below the IEEE C95.3 standard of 1.6 W/kg.

In a pioneering effort, this research presents a distinctive transformation of the Government College University Faisalabad (GCUF) logo into an RFID tag antenna using characteristic mode analysis (CMA), which resonates at the entire ultra-high frequency (UHF) radio frequency identification (RFID) band for IoT applications. The logo of GCUF is simulated in a computer simulation technology (CST) microwave studio to execute its four characteristic modes at 900 MHz. With the implementation of minor changes in the GCUF logo, optimal conjugate impedance matching with the RFID chip has been achieved. The impedance, reflection coefficient, and far-field pattern are examined through CST. The logo tag antenna is fabricated using a Rexin substrate (artificial leather) coated with conductive paint and a passive UHF RFID Alien Higgs H3 chip attached to the logo for impedance matching. The proposed design has been simulated with a human body model. The read range of the fabricated prototype is tested on different objects, like a notebook, T-shirt, and bag. The measured read range demonstrates the robustness of the proposed logo design across various distances: 3 m for a notebook and bag, and 2 m for a T-shirt, with RSSI values of −61 dB, −59 dB, and −62 dB, respectively.

A bandpass filter with reconfigurable band traps operating in the S-band with a wide tuning range for the transmission zeros is presented in this article. The filter employs a main transmission line path comprising two different step impedance resonator structure, with stopband formation achieved through four quarter-wavelength resonators coupled to both ends of the main path. These resonators folded into open-ring to decrease the area of the circuit, are loaded with reconfigurable elements (SMV2020), controlled via a voltage-based control system. The voltage control system, which is designed by microcontroller unit (MCU)-AT32F421K8T7, can change the power supply voltage linearly to make this filter system flexible. The filter is fabricated on a Rogers 4350 substrate with a relative dielectric constant of 3.66, a loss tangent of 0.004, and a thickness of 0.762 mm and simulated in high-frequency structure simulator. The filter demonstrates favorable passband characteristics on either side of the stopband, achieving an in-band insertion loss of less than 1 dB and a return loss exceeding 12 dB. The reconfigurable stopband spans from 2.1 to 3.0 GHz, with a stopband return loss greater than 13 dB and an out-of-band rejection exceeding 50 dB.

This paper presents the first reported design of a balanced nonreciprocal bandpass filter with both common-mode (CM) and differential-mode (DM) reflectionless characteristics. The nonreciprocal behavior is achieved using a time-modulated resonator, which isolates in-band backward interference signals, thereby protecting preceding circuits from their negative effects. To solve the negative effects of reflected waves of the reflection-based CM noise suppression and reflection-based DM stopband attenuation, CM and DM reflectionless structures are integrated at both the input and output ports, ensuring reflectionless operation for both CM and DM signals. Meanwhile, the implementation of DM reflectionless characteristics effectively addresses the issue of reflection zero degradation typically observed in time-modulated resonator-based nonreciprocal filters. The proposed filter exclusively transmits differential forward signals, which will greatly improve the anti-interference ability and stability of the balanced RF circuits. To validate the concept experimentally, a 1.5-GHz microstrip prototype is designed, simulated, fabricated, and characterized.

In this paper, a highly integrated wideband 3 × 3 Nolen Matrix with inherent filtering characteristics is proposed. It is based on an arbitrary-phase-difference (A-PD) filtering coupler and phase compensation networks. The proposed A-PD filtering coupler, composed of three groups of coupled lines, offers outstanding advantages, including wide bandwidth, flat output distributions, high frequency selectivity, and compact structure. To address the challenges introduced by the series topology of the Nolen matrix, a differential phase shift network and a phase slope adjustment network are incorporated, ensuring a constant phase difference between stages and minimizing in-band phase errors at the output ports. By integrating the A-PD filtering coupler with the phase compensation networks, a compact Nolen matrix centered at 3.5 GHz is realized, occupying only 0.5 λg × 0.5 λg. Measurement results validate its excellent performance, demonstrating an overlapping bandwidth exceeding 50% under the criteria of 10-dB return loss, 3-dB passband, ±1 dB amplitude imbalance, and ±5° phase difference error. Furthermore, the design achieves over 15 dB stopband rejection.

A hybrid Balanced Frequency Doubler working up-converting from 2.45 to 4.9 GHz using packaged GaN HEMTs and with no amplification stage, was designed and its performance validated with measurements. The design procedure is detailed, including a brief study of the HEMT optimum bias point. Moore space filling curves are used in the design of the input hybrid coupler, to reduce its size at the fundamental frequency. A maximum measured conversion gain of 11.5 dB with a second harmonic output power of 26.3 dBm was obtained, while fundamental and third harmonic suppression exceeds 40 dBc.

Gallium nitride technology takes advantage of the survivability for low-noise applications, while SiGe and GaAs technologies are recognized for the better noise figure (NF). In this paper, the technique for implementing inductive source degenerated HEMTs in all the stages to have a better NF is combined with a technique of high value gate bias resistor (RGB) to improve survivability. Moreover, this work includes the dependence of the reverse recovery time on different values of RGB with respect to the trap phenomenon and the RC time constant. The designed low-noise amplifier (LNA) achieves an NF better than 1.4 dB for 7.5–11.5 GHz, OIP3 up to 33 dBm, input reflection coefficient better than −8.4 dB, and output reflection coefficient better than −11.1 dB. NF has a minimum of 1.15 dB at 9.9 GHz. The small-signal gain of LNA is better than 15.3 dB in the whole frequency band, and the output power at 1 dB gain compression is 23 dBm at 11.5 GHz. LNA survives an input stress level of up to 39 dBm. The dimensions of the designed LNA MMIC are 2.9 mm × 1.3 mm.

A metamaterial absorber is proposed that features multiple absorption peaks ranging from 2 to 20 GHz, tailored for multiband radar applications. It employs low-cost FR4 dielectric as the substrate material and has a compact footprint of 0.0068$\lambda _o^2$. The multiband absorption properties of this absorber are crucial at microwave frequencies for radar applications, particularly for reducing radar cross-section and providing electromagnetic interference shielding. The miniaturized version of this absorber acting as a biosensor at THz range features multiple absorption bands, surpassing the count of comparable biosensors. This enhancement increases the sensing resolution and provides greater resistance to false peak shifts. The proposed biosensor exhibits a remarkable sensitivity of 4.64 THz/RIU, enabling the detection of even slight variations in refractive index, thereby enhancing cancer detection compared to recent studies. The analysis indicates that it achieves an impressive absorption rate of over 90% across all operating frequencies, with a peak Q-factor of 90.71, enhancing the interaction between THz waves and biomolecules, thereby ensuring precise detection. This absorber shows a stable response across various polarization angles and reaches optimal absorption for incident angles from 0° to 60° for both transverse electric and transverse magnetic waves. This works facilitates the detection of cancer among humans at the earlier stage with a portable and cost-effective sensing device.

This paper presents a metamaterial-inspired, left-handed circularly polarized (LHCP), high-gain, and miniaturized antenna with a radiation efficiency of 92.8%. A properly arranged metamaterial containing a 4 × 4 array of unit cells is placed on the ground plane of the microstrip antenna to increase the antenna’s gain up to 12.8 dBi at 10.3 GHz. Both the unit cell and the antenna are designed on an FR4 substrate with a loss tangent of 0.02 and a relative permittivity of 4.4. The overall dimensions of the designed antenna are 0.88λ0 × 0.88λ0 × 0.052λ0, where λ0 is the free-space wavelength at 9.8 GHz. The simulated bandwidth of the prototype antenna is 2.8 GHz (9.9–12.7 GHz), while the measured bandwidth is 3.2 GHz (9.8–13 GHz). The maximum simulated and measured gains are 14.4 and 12.8 dBi, respectively, at frequencies of 10.4 and 10.3 GHz. Achieving such high gain in a small LHCP antenna is the novelty of our antenna design. The bandwidth of the proposed antenna lies within the upper X-band and lower Ku-band. Therefore, this antenna is suitable for applications such as weather monitoring and air traffic control systems.