Class-D amplifiers offer significant potential for achieving efficient and high-power RF amplification. By converting the collector dissipation of conventional amplifiers into load power components and employing filtering to eliminate unwanted frequencies, Class-D amplifiers achieve superior overall efficiency. This study proposes and investigates a high-efficiency push-pull Class-D power amplifier integrated with a carefully designed matching network. To validate the proposed amplifier’s performance and practical applicability, a proof-of-concept circuit was designed and fabricated. Operating within a frequency range of 7.7 –8.7 MHz, the amplifier achieved notable results, including a power-added efficiency of 89.26% and an output power of 49.54 dBm. The consistency between simulated and measured results underscores the reliability of the proposed design and its potential for practical deployment. This work demonstrates the suitability of the amplifier for wireless Radio Frequency Identification applications, offering a highly efficient solution with enhanced output power and performance. To the best of the authors’ knowledge, this study provides a novel approach to achieving exceptional efficiency and output power, representing a significant advancement in the field of RF power amplifier design.

A compact antenna aperture tuner for an inverted-F antenna is presented using a high-voltage enhancement-mode p-GaN gate high electron mobility transistor (HEMT) RF switch with a gate length of 0.5 µm. The proposed design achieves a breakdown voltage of 100 V for a single p-GaN HEMT switch, enabling the replacement of conventional stacked high-voltage RF metal-oxide-semiconductor field effect transistor (MOSFET) configurations. A 4-bit switched-capacitor network based on p-GaN HEMT devices is employed to cover the n77 (3.3–3.8 GHz) cellular frequency band. Measured results show that a return loss exceeding 6 dB is obtained at the antenna feed point over more than 90% of the target frequency range. Under a continuous wave of 34 dBm, the measured reflected second- and third-order harmonics (H2 and H3) are −56 and −75 dBm, respectively. These results demonstrate the feasibility of p-GaN HEMT-based RF switches for compact and high-voltage antenna tuning applications.

The pronounced phase noise issue in millimeter-wave (mm-wave) complementary metal oxide semiconductor (CMOS) voltage-controlled oscillators (VCOs) has motivated a wider loop bandwidth in integer-N phase-locked loops (PLLs). In this work, we introduce a quadrature-phase spurious-tone-canceling phase detector (QSC-PD) that decouples the inherent trade-off between PLL loop bandwidth and spurious tone suppression. By incorporating an auxiliary sampling phase detection path, the spurious signals produced by the primary path are effectively canceled without extra power overhead or compromising loop stability. Owing to its high gain, the QSC-PD reduces its own jitter contribution within the loop bandwidth. Furthermore, the QSC-PD facilitates both frequency acquisition and VCO lock detection. Implemented in 0.13 μm SiGe bipolar CMOS technology, the mm-wave PLL attains a spurious tone of −84.5 dBc, a phase noise of −112 dBc/Hz at 1 MHz offset, and a minimum integrated jitter of 57.9 fsrms (1 kHz–300 MHz) at 15.6 GHz. The entire circuit consumes 39.6–44.5 mW.

In this paper, we present an ultra-fast technique for brain tumor detection in microwave brain imaging systems based on compressive sensing (CS). To achieve this, we designed an elliptical array-based microwave imaging system by simulating sixteen elements of modified bowtie antennas in the CST medium around a multi-layer head phantom. Additionally, we designed an appropriate matching medium to radiate in the desired band from 1 to 4 GHz. The algorithm section of our technique involves pre-processing steps for calibration, a processing step to create a two-dimensional image of the received signals, and a post-processing step for CS. In the processing section, we used a confocal image-reconstructing method based on delay and sum and delay, multiply, and sum beam-forming algorithms. Finally, we applied a new CS technique that includes an L1-norm convex optimization method to reconstruct low-dimension images from the original reconstructed images. We present simulated results to validate the effectiveness of our proposed method for precisely localizing the tumor target in a human full head phantom. The simulated results demonstrate that by using our proposed CS method, the image reconstruction processing time decreased to 63% and the compressed image size reduced to 25% of the original image.

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 paper presents a novel planar balanced-to-balanced diplexer with high isolation and harmonic suppression. Both the lower and higher channels of the diplexer consist of the two-stepped impedance resonators and one uniform impedance resonator. To enhance the inter-channel isolation of the diplexer, the cross-coupling between the resonators is used to introduce extra out-of-band transmission zeros. By utilizing stepped impedance resonators with different impedance ratios, the harmonics of the three resonators, except the fundamental harmonics, are different from each other so as to suppress the odd- and even-mode harmonics effectively and ultimately to achieve the purpose of broadening the stopband and enhancing the common-mode (CM) suppression. To verify the feasibility of this design, a microstrip prototype with dual-channel center frequencies of 2.01 GHz and 3.54 GHz was manufactured. Experimental results demonstrate that the in-band differential-mode (DM) isolation is higher than 41.6 dB and 41.5 dB for the lower and higher channels, respectively. CM suppression is greater than 20 dB in the 0–13.7 GHz range for the lower channel and 20 dB in the 0–9.0 GHz range for the higher channel. The stopband suppression level achieves 20 dB up to 18.5 GHz.

This paper presents a quad-port triplexer structure designed for next-generation wireless portable devices. The proposed triplexer consists of three bandpass filters isolated from one another. Filters 1 and 2 are designed using identical coupled line structures with varying physical properties, while filter 3 is developed with a novel coupled line structure. The modified coupled line enables a compact triplexer design, enhances isolation and bandwidth, and reduces the insertion loss. A comprehensive analysis of the proposed triplexer is conducted, and the S-parameter response demonstrates that the triplexer operates at 2.91, 4.43, and 1.20 GHz, with fractional bandwidths of 30.2$\%$, 22$\%$, and 33.3$\%$, respectively. The in-band return loss is better than 12.3 dB across the entire passband. Additionally, the triplexer features three transmission poles for the first two passbands and two for the third. The in-band insertion loss is less than 0.63 dB for all three passbands. The measured performance of the fabricated triplexer closely corresponds to the simulated results, validating its effectiveness in achieving the desired specifications. This makes the triplexer highly suitable for 5G networks and IoT-based wireless communication devices that demand multiband, high-performance filtering.

Inductive wireless power transfer (WPT) systems require compensating capacitors to operate efficiently. However, these capacitors can introduce additional costs, weight, and losses, particularly at MHz-range operating frequencies. To mitigate these issues, self-resonant coils can be used by exploiting the parasitic capacitances inherent in double-layer printed circuit boards (PCBs). In this work, a double-layer coil for a self-resonant series WPT system is developed for operation at the AirFuel standard frequency of 6.78 MHz. Unlike conventional design methods adopted for self-resonant coils, mainly based on analytical formulations, the proposed approach employs Finite Element Method simulations that couple electro-quasistatic and magneto-quasistatic formulations. This approach enables accurate evaluation of the self-resonant frequency (SRF) as well as the current distribution along the PCB layers, revealing significant non-uniformity. Building on this insight, copper trace length is reduced to save material while maintaining performance in terms of operating frequency. Both the full-trace and reduced-trace coils are fabricated and tested, showing good agreement with simulations. Notably, the proposed reduction in the copper trace affects the SRF by only 3% compared with the full-trace design.

In this paper, a dual-frequency switchable wireless power transfer (WPT) system based on parity–time (PT) symmetry is proposed. For the transmitter, a high-efficiency switch-mode amplifier is employed as the negative impedance to provide the required gain. To realize dual-frequency operation, the magnetic coupling coil is designed as triple-tap structure which can be used to create two distinct series inductor-capacitor (LC) resonant branches by switch. At the receiver, two parallel inductor-capacitor-resistor (LCR) resonant circuits with corresponding dual operational frequency of transmitter are adopted to achieve stable energy reception. The transmission characteristics of the system under different frequency switching modes are analyzed theoretically and verified experimentally. The results demonstrate that, whether operating in the low- or high-frequency mode, the system can maintain the PT-symmetric state in the strong coupling regime, achieving robust and efficient WPT with system efficiency >80%. The proposed dual-frequency switchable WPT system can offer a theoretical reference for practical reconfigurable wireless charging applications requiring dual operating frequencies.

This paper presents a novel self-octuplexing substrate-integrated waveguide (SIW) cavity-backed slot antenna for eight-band wireless communication services. This antenna employs eight semi-elliptical-shaped slots on an octagonal SIW cavity with different lengths to radiate at eight different frequencies. The eight radiating frequencies are 2.7, 3, 3.3, 3.6, 3.9, 4.2, 4.5, and 4.72 GHz, with impedance matching is less than −10 dB. Each radiator is backed by an eighth-mode SIW cavity and excited by a 50 Ω microstrip line. A designed prototype of the antenna is fabricated and tested. It has more than 34 dB measured isolation among any two ports. The maximum measured antenna gains are 4.4, 4.19, 4.11, 4.03, 4.19, 4.28, 5.2, and 5.44 dBi at the respective operating frequencies. It has a measured cross-polarization level of below −24.2 dB in the boresight direction and a front-to-back ratio of more than 10.4 dB in all the bands. All the slots can be tuned independently to radiate at the desired frequency band. This antenna can easily be integrated with other planar circuits due to an unperturbed ground plane.

One of the most popular designs for an antenna array is the non-uniform concentric circular antenna array (CCAA). This study discusses the design challenges of the CCAA with a non-uniform multi-ring structure positioned in the $x$–$y$ plane that aims to enhance the first null beam width (FNBW) and the optimal sidelobe level (SLL). The Jaya algorithm, Novel Particle Swarm Optimization, and Particle Swarm Optimization (PSO) have been used to address those challenges. In this work, non-uniform ring radii and element positions are considered. Adjusting inter-element spacing and feeding current yields an array layout with the best SLL. This work enhances FNBW and superior SLL reduction. Using these methods, it computes additional antenna array parameters such as maximum beam, total effective aperture, maximum directivity, maximum effective aperture area, total beam area, radius, and circumference of the CCAAs. The proposed algorithm, Craziness Particle Swarm Optimization (CRPSO), has attained superior SLL reduction compared to other optimization algorithms and also compared with other existing works.

This paper presents a wideband dual-polarized microstrip patch antenna with a dual-layer design to meet the requirements of high isolation for in-band full-duplex (IBFD) communication systems. The antenna improves upon the traditional square patch with four Γ-shaped probe-fed by ingeniously extending the metal strips of the Γ-shaped probes to form a cross-shaped structure, thereby exciting multiple independently tunable resonant modes. A circular ring slot is etched at the feed point to optimize the antenna impedance matching. Finally, a middle-layer circular patch is added to optimize the high-frequency impedance matching without changing the profile. By combining differential feeding technology, the antenna maintains a low-profile characteristic of 0.086λL (where λL denotes the free-space wavelength at the lowest operating frequency) while achieving dual-polarized operation and high port isolation (≥42 dB), along with an impedance bandwidth of 71.5% (4.06–8.58 GHz) that surpasses most existing designs. The measured antenna realized peak gain is 8.2 dBi, with cross-polarization suppression ≤−20 dB and stable radiation pattern characteristics across the operating frequency band. This design provides a compact antenna solution with high isolation, broadband, dual polarization, and low cost for IBFD applications.

This paper presents a novel dual-band cylindrical dielectric resonator antenna featuring a distinctive cross-ring structure that enables circular polarization (CP) across two critical frequency bands. The proposed antenna operates efficiently in both the 8–16 GHz microwave band and the 24–30 GHz millimeter-wave band, making it particularly suitable for ultra-wideband (UWB) and emerging 6G applications. Examination of the $S_{11}$ parameters reveals excellent impedance matching below $-10$ dB, yielding an impressive bandwidth of approximately 8 GHz (64.26%) in the lower band and approximately 6 GHz (23.72%) in the upper band. The antenna achieves stable CP through degenerate orthogonal modes, i.e., $\mathrm{TM}^{x}_{11\delta}$ and $\mathrm{TM}^{y}_{11\delta}$, in the cylindrical dielectric resonator, with 3-dB axial-ratio bandwidth extending across both operating bands (approximately 8 GHz in the UWB band, representing 54.91% bandwidth, and approximately 6 GHz in the mmWave band, representing 20.12% bandwidth). The antenna delivers consistent gain performance, averaging 7.0 dBi in the UWB band and 6.5 dBic in the mmWave band. The novelty of this design lies in its elegant cross-ring feeding structure that simultaneously enables dual-band operation, excellent CP characteristics, and high radiation efficiency in a compact form factor. Simulation results closely align with measured data, confirming the antenna’s suitability for next-generation wireless communication systems.

This work proposes a novel design in which a multi-cavity backed substrate integrated waveguide (SIW) slot antenna is designed with bow-tie uneven eclipse slot radiating in X-band to achieve high gain and bandwidth. The antenna cavities are arranged linearly for dual, triple and penta structure with modified slot loaded in it. The closely spaced hybrid modes generated in each cavity shows strong loading effect that combines to get broadband response. Microstrip to SIW feedline transition gives power to the antenna. The constant dimension of the slot acts as an array that increases the peak gain from 5.8 dBi in dual cavity to 8.49 dBi in triple cavity to 9.2 dBi in penta cavity structure. The bandwidth of the antenna is 770 MHz in dual cavity, 1.2 GHz in triple cavity and 940 MHz in the penta cavity. Beam steering is also achieved in the penta cavity structure that can be used in various application in which multi-oriented communication is required. The antenna has been simulated in Ansoft HFSS v.2023. The experimental and simulated results agree well that confirms the proposed designs in X-band. The proposed antenna can be used in the application where there is requirement for wideband, high gain, and directional pattern.

A mantle cloak with a novel unit cell design is proposed for the scattering suppression of cylindrical metasurfaces. The proposed cloak is designed for an electrically small cylindrical object. The Mie Theory is employed to calculate the surface impedance of the mantle cloak, which plays a critical role in determining the optimal design parameters. The unit cell parameters necessary for the design are obtained by analyzing the surface impedance. Bistatic Radar Cross-Section (RCS) analyses have been conducted for the cloaked and uncloaked cases of cylinders. The designed cylinder demonstrated remarkable scattering suppression at the operating frequency. Furthermore, the results obtained from the novel unit cell design are compared with findings in the literature, underscoring the improved cloaking performance achieved with the new design. As a demonstration, a single-layer novel unit cell cloaked cylinder is constructed with a total radius equal to 13 percent of the free-space wavelength, a total length corresponding to 1.94 times the free-space wavelength, and a dielectric spacer thickness of 1.27 percent of the free-space wavelength. This single-layer novel unit cell mantle cloak achieves a 16.65 dB total RCS reduction at 3.1 GHz, with a notable decrease in scattering at the operational frequency in all directions.