The characterization of biological objects with microwave spectroscopy is getting increasing interests, as it is label-free and noninvasive. To perform their analysis, 2-port sensors are present in the literature, enabling only partial investigations of 3D biological samples, without taking their structural heterogeneity into account. Within this context, a 4-port microwave-based biosensor dedicated to microtissue characterization is proposed, in order to extend the sensing capabilities of microwave dielectric spectroscopy and provide electrical responses of 3D biological models subdivisions. An electrical model suitable for such a multiport device is established to extract the characteristics of the different sections of the 3D entity. The modeling methodology exploits the symmetry of the microwave component, while applying a common and differential modes approach derived from the measured 4 ports scattering parameters. After the mathematical validation of this approach, different elementary models are evaluated. Ethanol-based aqueous solutions are first used for their homogeneity within the fluidic channel. Polystyrene beads exhibiting two different diameter sizes are then numerically and experimentally investigated due to their 3D configuration and their uniform and known permittivity. This study demonstrates that the 4-port sensor and associated electrical model enable to consider electrical subdivisions of the 3D entity under test, based on the localization of the object on the different microwave electrodes. This constitutes the first step toward the analyses of complex and heterogeneous 3D biological models such as microtissues.

In this paper, an ultra-wideband, low-scattering, and stable-gain Fabry–Perot antenna is proposed based on a novel hybrid metasurface. The radar cross-section (RCS) reduction is achieved by employing a 1-bit checkerboard polarization conversion metasurface (PCM) with a high polarization conversion ratio. Moreover, to enhance the antenna gain, broaden the 3-dB gain bandwidth, and maintain stable gain performance within the passband, a nonuniform reflective metasurface with a positively sloped reflection phase is strategically introduced. This metasurface, combined with the tessellated PCM layer, forms a hybrid structure featuring high transmission efficiency. Benefiting from this hybrid metasurface design, the antenna demonstrates a maximum gain enhancement of 4.7 dBi, an average gain improvement of 2.7 dBi, and a 39.8% increase in the 3-dB gain bandwidth. To validate the proposed design methodology, a prototype antenna was fabricated and experimentally measured. The measured results show good agreement with the simulated predictions. Specifically, the fabricated antenna exhibits a –10 dB impedance bandwidth of 22.47% (7.23–9.06 GHz), a 3-dB gain bandwidth of 18.2% (7–8.4 GHz), and a maximum gain of 17.25 dBi at 7.2 GHz. Additionally, the antenna achieves an RCS reduction bandwidth of 102.3%, with a maximum RCS reduction of 35.3 dB at 13.03 GHz.

Radio frequency (RF) coaxial connectors are crucial in high-speed digital systems for data transmission. Connectors applied in harsh environments will be degraded over time, affecting the signal integrity. At present, a suitable equalization technology is of substantial value for enhancing the quality of high-speed signal transmission. However, there is limited research focusing on specific equalization designs for degraded connectors. In this current work, based on the theoretical analysis, simulations validation and experimental testing, an equivalent circuit model of the degraded connector was developed. Furthermore, an equalization structure consisting of series resistance and capacitance was proposed. The transmission loss caused by the connector degradation was compensated effectively using this method. Meanwhile, eye diagram characteristics were improved significantly at the receiver where zero timing jitter and an almost full eye opening were achieved. Equalization enhances the eye opening factor by over 50% compared to the uncompensated system. This paper integrates electrical contact theory with high-speed equalization design. Tools and guidance were provided through the proposed modeling techniques for studying equalization effects of this degraded connector system in designs and applications.

In this article, a 1 × 2 bandwidth (BW) and frequency-reconfigurable dielectric resonator-based multiple input multiple output (MIMO) antenna array is presented for 5G sub-6 GHz (3.3–6.0 GHz)/Wi-Fi 6E (5.925–6.425 GHz)/Wi-Fi 5G (5.15–5.85 GHz) applications. Additional dual-ring-open loop resonator structures with varied dimensions are introduced within antenna’s feeding network to achieve BW and frequency reconfigurability. RF PIN and varactor diodes (VDs) are integrated with proposed structure to enable switching between various modes and continuous tuning of frequency and BW, respectively. Further, Taguchi neural network (TNN) has been incorporated to predict percentage bandwidth of proposed antenna, getting a maximum deviation of only 0.6% from actual value. The proposed structure operated from 4.98 to 6.5 GHz, achieving wide continuous frequency tuning of 20.36% in passband and 6.1% reconfiguration for notch band. It also demonstrates continuous BW tunability from 16.69% to 34.44% with measured BWs of 19.58%, 34.44%, and 16.69% at 0, 3, and 8 V reverse bias voltages of VDs, respectively. MIMO antenna array structure also shows enhanced gain performance with a peak gain of 11.03 dBi and an overall gain above 7 dBi in the whole operating band.

This paper introduces a high-power, compact active integrated antenna with extended voltage tuning capability, featuring a nearly 1 GHz oscillation range in the X-band (8.35–9.21 GHz). This broad frequency range enhances the oscillator’s flexibility and adaptability for advanced applications in radar systems and wireless communication. The design integrates InGaAs HEMT technology using a feedback circuit. The self-oscillating antenna, manufactured on a RO4003C substrate with a height of 0.508 mm and dimensions of 0.23 × 0.27 ${{\lambda}}_0^2$, demonstrates impressive performance through small- and large-signal analyses. The obtained results are based on harmonic balance simulation using the auxiliary generator technique within the Advanced Design Systems (ADS) tool. Simulation results indicate power levels from 10.928 dBm to 8.062 dBm, while measured output power ranges from 10.90 dBm to 7.916 dBm, and Equivalent Isotropically Radiated Power (EIRP) values were between 12.68 dBm and 10.198 dBm in the interval 8.35–9.21 GHz. Phase noise measurements are −102.94 dBc/Hz at 1 MHz and −124.13 dBc/Hz at 10 MHz. The simulated and measured results are in good agreement, highlighting the robustness and reliability of the oscillator, as well as the effectiveness of the design, which is well suited for applications requiring high stability, precise frequency control, high output power, and efficient performance for microwave applications.

In many wireless power transfer (WPT) scenarios, to prevent lateral misalignment between the transmitter (Tx) and the receiver (Rx) and to implement a stable power transfer, multiple Txs are used in place of a single Tx. The existing multi-Tx structures lack flexibility in assembly due to wired connections between Tx units, and face the challenge of variation in power delivered to the load (PDL) in the over-coupling region. A self-organized parity-time (PT) symmetric WPT system comprising dual independent Tx units is proposed in this paper. It provides two operating modes by activating one or two Tx units, offering not only a stable but also an identical PDL. This is achieved by strategically using a scaled PT-symmetric structure when activating only one Tx unit with a scaling factor of 2, and synchronizing the oscillation when activating dual Tx units with the help of existing mutual coupling between them. The theoretical analysis is validated by simulations and experiments. The proposed structure addresses the performance valley region that exists between two side-by-side traditional single-source single-coil structures. Moreover, compared to traditional single-source dual-coil structures, it extends the lateral transfer range rate from 20% to 100% and offers flexibility in assembly.

Respiratory and cardiac rates can be estimated by analyzing a spectrum of linearly mixed phase fluctuations in a radar echo of an individual. However, there are high-order harmonics caused by time-varying respiratory rate, and the interference effect of the respiratory rate and its harmonics makes it difficult to estimate the cardiac rate with relatively low energy in a spectrum. To solve this problem, we exploit the independent component analysis method with dual-band distributed continuous wave radar for effective decomposition of phase fluctuations corresponding to respiratory and cardiac rates. In simulations and experiments, the respiratory and cardiac rates were successfully estimated by the proposed decomposition method, compared with conventional methods.

A ϕ2.5 m Gregorian antenna has been designed, analyzed, developed, and tested for a contoured beam for India and its Islands. The downlink band is 11.7–12.2 GHz. Uplink band is 17.3–17.8 GHz. The frequency band ratio is 1:1.52. The feed system consists of a radial corrugated horn and a turnstile orthomode transducer. Since there is a common feed system for Ku-Tx and Ku-Rx bands, it causes a large variation in the phase center for Tx and Rx bands. This large disparity in Tx and Rx phase center makes shaping challenging to achieve higher edge of coverage (EoC) gain, over widely separated transmit and receive bands. The optimization is carried out to achieve enhanced EoC gain and compliance of cross-polar isolation (XPI) through surface shaping of main and sub-reflectors. We have also optimized the feed coordinate to achieve the goal. The scattered near field at feed aperture is also minimized to get good XPI. Minimum radius of curvature of the surfaces has been controlled, which is required for the manufacturing of sub- and main-reflectors with minimum fabrication error. A new technique has been devised for the accommodation of a Gregorian antenna on a spacecraft with suitable radio frequency (RF) clearance. The impact of photogrammetry targets on RF performance is also brought out in the article.

This paper presents a broadband rectifier based on GaN high electron mobility transistor (HEMT). The continuous class-B/J rectifier operation mode is analyzed in detail. The relationship between the continuous mode class-B/J rectification efficiency and the output capacitance Cout and the on-state resistance Ron is built and the rectification model is firstly presented. Then, the available impedance design space can be determined based on the rectification efficiency model. Considering the package parameters of the CGH40010F, design space at the package plane has been presented. Moreover, a broadband phase tuning network (PTN) is adjusted to satisfy this impedance space. Thus, a broadband transistor-based rectifier can be designed using the continuous class-B/J mode and the PTN. For validation, a rectifier working in 2.4–3.3 GHz was fabricated using CGH40010F. The rectification efficiency varies from 66% to 78% when RF input power is 10 W. Compared with other transistor-based rectifiers, the presented rectifier has a competitive working bandwidth.

In this paper, a dual-band dual-circularly polarized (CP) patch antenna with integrated coupling structure and stepped impedance resonators (SIRs) is proposed. The tapped-line coupling generates $0^{\circ}/180^{\circ}$ phase in two frequency bands, while the parallel coupled-line coupling exhibits an inherent $90^{\circ}$ phase delay in two frequency bands. The two-way coupling structure generates the $\pm90^\circ$ phase shift enabling dual-CP, eliminate the need for additional phase shifters. Then, the SIRs excite the two orthogonal modes of the radiation patch while concurrently matching the impedance between the antenna and the input port, eliminating the need for an additional matching network. Finally, the radiation patch and SIRs are integrated into a complete structure, and a T- junction is used to connect the two branches. Compared to traditional design, the proposed antenna greatly reduces the complexity and difficulty. The development stages are discussed in detail. The proposed design is demonstrated through prototype fabrication and characterization.

Hand gesture recognition (HGR) has gained significant attention in human-computer interaction, enabling touchless control in various domains, such as virtual reality, automotive systems, and healthcare. While deep learning approaches achieve high accuracy in gesture classification, their lack of interpretability hinders transparency and user trust in critical applications. To address this, we extend MIRA, an interpretable rule-based HGR system, with a novel gesture onset detection method that autonomously identifies the start of a gesture before classification. Our onset detection approach achieves 90.13% accuracy on average, demonstrating its robustness across users. By integrating signal processing techniques, MIRA enhances interpretability while maintaining real-time adaptability to dynamic environments. Additionally, we introduce a background class, enabling the system to differentiate between gesture and non-gesture frames and expand the dataset with new users and recordings to improve generalization. We further analyze how feature diversity affects performance, showing that low diversity can suppress personalization due to early misclassifications. Using a foundational and personalized rule framework, our approach correctly classifies up to 94.9% of gestures, reinforcing the impact of personalization in rule-based systems. These findings demonstrate that MIRA is a robust and interpretable alternative to deep learning models, ensuring transparent decision-making for real-world radar-based gesture recognition.

This paper proposes a highly selective dual-band bandpass filter (BPF) utilizing hemispherical resonators and an in-band transmission zeros (TZs) method. For obtaining high isolation between two passbands, a compound resonator topology is realized by arranging six hemispherical cavity resonators (HCRs) in a two-by-two vertical configuration, and then three TZs between the passbands are introduced. The filter selectivity is further optimized through elaborately placing three metal pillars in the cavity, and then one TZ in the lower stopband and two in the upper stopband are generated. Notably, the size of the HCR is reduced by about 50% compared to the conventional spherical resonator. To validate the design, a dual-band filter is 3D printed, which operates at 9.1 and 9.77 GHz with bandwidths of 210 and 200 MHz, respectively. The measured results show good agreement with the simulated ones.

In this study, a metasurface (MS) polarization converter combined with a two-port dielectric antenna is constructed and studied. The feeding configuration, which consists of a printed line connected to an aperture, offers built-in filtering capabilities. In addition to converting linear to circular polarization between 2.49 and 3.25 GHz, the suspended MS layer enhances port isolation to less than −20 dB. In addition, the suggested radiator’s |S11| is projected using the Random Forest and XGBoost machine learning (ML) models, which demonstrate satisfactory agreement with simulation data. The antenna effectively functions over 2.33–3.35 GHz, demonstrating that it is a leading contender for sub-6 GHz 5G communication systems. Fabricated measurements support both simulation and ML predictions.

This paper presents two distinct configurations of a GaN-based digital transceiver (TRx) to evaluate their performance and integration efficiency. The first configuration, features a novel low-noise amplifier with integrated switching capability (LNAiS) and a digital class-E power amplifier (PA) on a single compact chip. The LNAiS eliminates the need for an external antenna switch, reducing module complexity and chip size while maintaining high performance. It achieves a gain of 12.7 dB and a noise figure of 3 dB at 4.7 GHz in Rx mode and provides over 20 dB isolation in Tx mode across 4.7–7.4 GHz. The digital PA demonstrates flexibility and efficiency, achieving 46% and 23% efficiencies for 20 MHz LTE and OFDM signals, respectively, and 22% for a 240 MHz OFDM signal with 10 dB PAPR. The second configuration integrates the same concept of digital PA with a standard LNA and an SPDT switch (LNAsS), achieving a gain of 24.8 dB and a noise figure of 2.65 dB at 4.2 GHz. This work highlights the trade-offs between these two architectures and demonstrates that the LNAiS-based approach drives the development of greener, more flexible, compact,lower-complexity, and cost-effective transceivers for 5G networks.

The impact of misalignment errors, specifically yaw and pitch deviations, on dihedral reflectors’ scattering responses is studied for millimeter-wave polarimetric multiple-input multiple-output automotive radars. Through simulations and experiments at 77 GHz, it is demonstrated that significant radar cross-section (RCS) variations of up to 30 dB can occur within small misalignment ranges (0$^{\circ}$–2$^{\circ}$). The findings emphasize that larger dihedral dimensions can amplify sensitivity to misalignment in some specific misalignment scenarios, offering trade-offs between reflection strength and robustness to misalignment errors. The study also explores near-field effects, revealing notable discrepancies between the dihedral near- and far-field scattering response in misalignment scenarios. A polarimetric calibration method is applied to show how polarimetric channel phase response is affected under such conditions, achieving stable results in specific configurations (e.g., dihedral at 0$^{\circ}$ under yaw misalignment angle). This study addresses key challenges in calibration accuracy, including the high sensitivity of RCS to small angular misalignments, the trade-offs between reflector dimensions and robustness, and the influence of near-field effects in practical setups.

An original analysis of Fabry–Perot cavity antennas based on thick partially reflecting sheet (PRS) is presented in this work. The bandwidth enhancement of such radiating devices with respect to Fabry–Perot cavity antennas based on thin PRS has been investigated through a leaky-wave, transverse-equivalent-network approach, and a field matching technique. This analysis led to an optimal condition for considerably improving the gain-bandwidth figure of merit for this class of radiating devices on a sound physical basis. A Fabry–Perot cavity antenna based on a thick PRS working at 60 GHz is discussed as a case study. An excellent impedance matching is finally achieved by means of an efficient feeding network designed through a fast ad hoc, hybrid, analytical-numerical method. Theoretical results are in an excellent agreement with full-wave simulations corroborating the proposed methods.

In this paper, we report an on-wafer High-Electron-Mobility transistor characterization method over a large frequency band [250 MHz–1.1 THz]. The transistor’s coplanar accesses were optimized to enable high-frequency measurement of the devices up to 1.1 THz. The characterization method implements an on-wafer multiline Thru-Reflect-Line calibration kit fabricated on indium phosphide (InP) substrate validated using comparisons between simulations and measurements of coplanar waveguide (CPW) devices. An 80-nm gate length InAlAs/InGaAs/InAs InP-HEMT was fabricated using the optimized transistor accesses then it was measured over the [250 MHz–1.1 THz] frequency band using the developed on-wafer characterization method. It is important to mention that the same transistor was measured on six different on-wafer test benches [250 MHz–110 GHz], [140–220 GHz], [220–325 GHz], [325–480 GHz], [500–750 GHz], and [750–1100 GHz]. The S-parameter measurement results show good continuity between the six measured frequency bands. Observations on the extracted gain measurements and a comparison between the measured and [250 MHz–110 GHz] extrapolated cut-off frequencies are also provided.

This paper presents the development and characterization of a wideband noise source, involving Commercial Off-The-Shelf components. The noise source relies on avalanche noise generation by driving the base-emitter junction of a packaged Si–Ge Heterojunction Bipolar Transistor into reverse breakdown. The paper discusses the noise source operation principle and its extensive characterization in both mm-Wave K band, as well as in C and X bands. Two prototypes were implemented without including output impedance matching, such as to preserve the wideband capabilities of the noise source. Performances were validated in terms of output Excess Noise Ratio (ENR), values reaching 10.8 dB were obtained for the K band at 6.71 mA breakdown current, in a 24–32 GHz bandwidth and $21-102^{\circ}\mathrm{C}$ device temperature excursion. A calibration model is also provided, which fits ENR fluctuations with an average error under 0.05 dB, when considering the maximum current and temperature excursions, as compared with 0.8 dB ENR drift reported for the non-calibrated source. The C and X band validation in 4–6 and 10–12 GHz frequency ranges highlights ENR reaching 25.6 and 22.6 dB, respectively, at 6.9 mA bias current.

Diabetes is increasingly recognized as a serious, worldwide public health concern. In this paper, an extreme learning machine (ELM) based on time-domain pulses was introduced to obtain noninvasive glucose detection. To validate the method, time-domain signals from different concentrations of glucose solutions were detected in the model. Considering that the glucose levels of diabetic patients range from 30 to 500 mg/dL, the glucose solution concentration was set to 10−500 mg/dL, with an interval of 10 mg/dL. The received signals were trained using the ELM algorithm, which was able to accurately predict solutions of unknown concentration with an average relative error of 1.45%. The proposed method is rapid to process, simple to operate, and highly accurate for noninvasive glucose detection. The results demonstrated that microwave detection technology combined with the ELM algorithm has the potential to become a valuable tool for noninvasive glucose monitoring in clinical settings.

This article presents germanium telluride (GeTe)-based switches for radiofrequency (RF) applications, capable of reversible switching between their ON and OFF states through optical activation by irradiation. Unlike previous studies, the transition is induced by infrared laser pulses at a wavelength of λ = 915 nm, which is highly promising for future integration of laser sources and the proposal of fully integrated optical activation of phase change material (PCM) switches. This represents a novel approach compared to the existing literature, which primarily focuses on the ultra-violet spectrum, less suitable for on-chip optical integration. Our work also provides combined optical and thermal simulations to elucidate the challenges associated with actuating small PCM switches and demonstrates the effectiveness of PCMs at this wavelength. The study achieves bistable switching at high frequencies up to 40 GHz, with a figure of merit of 31.5 fs, despite the low GeTe conductivity of only 1.85·105 S/m. Additionally, significant advancements over the literature have been made by surpassing 30,000 cycles with optical actuation.