A superstrate comprising a dielectric and metasurface pattern, placed at an optimum height from the antenna surface, can facilitate radar cross section (RCS) reduction of the antenna. An optimally designed superstrate will not degrade the radiation performance of the antenna. In this paper a novel design of low RCS superstrate-based right-handed circularly polarized (RHCP) cavity-backed Archimedean spiral (CBAS) antenna has been presented. The superstrate consists of a resistive sheet based metasurface pattern on the top layer and a metallic pattern on the bottom surface of dielectric substrate. It is shown that the proposed thin (0.82 mm) superstrate placed at an optimal height of 19.2 mm from the antenna surface resulted in the RCS reduction of 6-8 dBsm over the operating frequency range (2-18 GHz), without any degradation in VSWR (< 2.1), gain (> 3 dBi), and axial ratio (< 3 dB). Such a low observable, cost-effective, and efficient spiral antenna without any payload constraints can be a preferred choice for electronic warfare applications in aerospace platforms.

This paper describes a flexible dual-port multiple-input multiple-output (MIMO) antenna system tailored for multi-band operation, covering 2.4 GHz Wi-Fi, 3.5 GHz 5G, as well as the 5-7 GHz band used in wireless applications such as Wi-Fi 7. The antenna is fabricated on a liquid crystal polymer (LCP) substrate, featuring an ultra-thin profile of 0.1 mm and a compact size of 60 × 35 mm², making it highly suitable for integration into modern flexible and wearable devices. To achieve high port isolation, a complementary split-ring resonator (CSRR) structure is incorporated between the two radiating elements. The measurement results indicate that the antenna achieves impedance bandwidths across 1.36-2.71 GHz, 3.07-3.655 GHz, and 4.015-8.245 GHz, which fully cover the target frequency bands of 2.4-2.483 GHz, 3.4-3.5 GHz, and 5.15-7.125 GHz. The antenna's performance is comprehensively characterized by evaluating key parameters including S-parameters, envelope correlation coefficient (ECC), diversity gain (DG), total active reflection coefficient (TARC), gain, mean effective gain (MEG), and radiation patterns, along with other relevant metrics. All measured results confirm that the antenna meets the essential requirements for MIMO and diversity systems. Furthermore, bending tests conducted at two distinct radii of 30 mm and 50 mm confirm stable antenna performance, verifying its mechanical robustness and reliability under practical bending conditions.

This paper presents a self-diplexing, multi-mode substrate-integrated waveguide (SIW) antenna based on a cavity-backed SIW configuration. The antenna employs a λ-shaped radiating slot that provides inherent filtering characteristics. The proposed architecture achieved independent dual-band control through two diagonally oriented slots arranged at 45°, forming a λ-shaped aperture. These slots, integrated within an SIW cavity and excited by two separate 50-Ω microstrip feeds, enable dual resonances at 10.76 GHz and 12.39 GHz, corresponding to the TE₂₁₀ and TE₂₂₀ modes for X-band and Ku-band operation, respectively. Experimental validation confirmed reflection coefficients below -10 dB in both bands, with measured bandwidths of 3.0% (10.61-10.93 GHz) and 3.2% (12.19-12.59 GHz). The proposed filtenna achieves gains of 6.12 dBi and 6.15 dBi and exhibits high port isolation exceeding 28 dB between channels, along with an overall simulated radiation efficiency of 91.16%. In addition, a single-layer structure offers two-band operation, broadside linear polarization, and intrinsic filtering functionality, making it a compact and efficient solution for X/Ku-band applications.

To address the limitations of Permanent Magnet Synchronous Motor (PMSM) speed-current closed-loop systems, including control performance degradation due to PI controller integral saturation and insufficient convergence in traditional model predictive current control (MPCC) while simultaneously reducing the computational load in the control system, this study combines model-free control theory with higher-order sliding mode methods and proposes an adaptive nonsingular terminal model-free sliding mode composite control strategy (ANTMFSMC) that considers parameter mismatch. First, based on the mathematical model of PMSM and the model-free theory for nonlinear systems, a speed-current loop control model is established. By combining the nonsingular terminal sliding mode with adaptive sliding mode reaching law, a speed-current loop ANTMFSMC controller is designed, and an improved exponential sliding mode disturbance observer (INTSMDO) is constructed to estimate the unknown components of the unmodeled dynamics and parameter uncertainties in the system. These estimates are then introduced as a feedforward compensation into the ANTMFSMC controller to form a complete composite control architecture. Finally, through simulations and experimental comparisons with traditional PI control and the traditional nonsingular terminal model-free sliding mode control based on sliding mode disturbance observer method (NTMFSMC-SMDO), the results show that the proposed strategy effectively suppresses d-q axis current and voltage ripple, significantly improves the convergence speed and anti-disturbance capability of the system, and demonstrates good engineering application value.

The focus of this study is the design of a multi-transmitter single-receiver wireless power transfer (MTSR-WPT) system, particularly for implantable medical devices such as brain pacemakers. Conventional charging methods rely on invasive surgery or frequent battery replacement, posing significant challenges for patients. To address this issue, this work proposes an MTSR-WPT system based on a flexible printed circuit board (FPCB). The designed small-coil array topology leverages the mechanical flexibility of FPCB to conform to complex biological surfaces, significantly enhancing two-dimensional omnidirectional anti-misalignment capability while reducing magnetic leakage during operation. To further compensate for misalignment between the transmitter and receiver, a backpropagation neural network optimized by the Seagull Optimization Algorithm (SOA-BP) is introduced for receiver coil position prediction, combined with a fuzzy PID control strategy for dynamic output voltage regulation. Simulation and experimental results demonstrate that under a fixed load condition, the proposed system achieves stable energy transfer within a 120 mm charging area, maintaining an output power exceeding 1 W when the receiver coil is positioned at a height of 20 mm. Compared with traditional single-coil systems, the optimized multi-coil array exhibits superior performance in both misalignment tolerance and magnetic leakage suppression. These results verify the effectiveness of the proposed MTSR-WPT system and highlight its potential for implantable medical devices and other power electronic applications, providing a novel solution for achieving efficient and reliable wireless energy transfer.

The demand for reliable and high-speed wireless communication in urban environments such as offices and densely populated areas is often hindered by signal obstructions. Reflectarray antennas offering beam steering capabilities through passive configurations have gained significant attention as a potential solution. However, existing designs at lower frequency bands struggle to achieve efficient phase variation within a single layer while maintaining high gain and consistent performance. In order to overcome these constraints, this work presents a reflectarray design that operates at 5 GHz. It utilizes a 15 × 15 multi-ring unit cell structure on a single-layer FR4 substrate to achieve a complete 360˚ phase variation. Two prototypes were fabricated to steer beams at 30˚ and 60˚, demonstrating the design's flexibility and adaptability for various application-specific requirements. The proposed reflectarray realizes a peak gain of 21 dBi and operates over a wide frequency range of 4.5-5.5 GHz, as validated through simulation and experimental results. The design effectively enhances signal coverage and addresses blockage challenges in urban areas, providing a practical solution for passive reflectarrays in Wi-Fi and similar wireless communication applications.

A comb-shaped antenna was designed, optimized and analyzed for an operational frequency of 2.4 GHz. The proposed design was modelled on an RT/Duroid 2880 substrate with dimensions 32 × 28 mm² and 0.8 substrate thickness. The antenna is designed to resonate at 2.4 GHz frequency band on substrate material. The body placement analysis of the proposed antenna was performed using human hand and leg phantom models, and the Specific Absorption Ratio (SAR) was less than 1.6 W/kg (ranging from 0-0.361 W/kg on hand and 0-0.267 W/kg on leg phantoms, respectively). The 3D radiation gains for both hand and leg are 4.95 and 4.81, respectively. Additionally, the vertical and horizontal bending losses were taken at 0˚, 30˚, 45˚, 60˚, respectively and their graphs were analyzed. Owing to its efficient and effective results, this antenna can be utilized for various biomedical applications.

The results of the propagation of electromagnetic waves in 1D periodic photonic waveguides and resonators are presented in this study. This structure consists of periodically arranged cells, with each cell containing parallel and series segments, grafted by two resonators at two different sites. This system creates passbands separated by photonic bandgaps, in which electromagnetic waves cannot propagate. The analytical calculation is based on the transfer matrix method (TMM), which aims to calculate the dispersion relation and transmission rate. Our results indicate the importance of the resonator length in applications such as guiding and filtering electromagnetic waves. This study also demonstrates how the addition of cells and the adjustment of resonator lengths influence the frequency selectivity, which is essential for filtering in communication technologies.

To address the inherent chattering issue in traditional sliding mode observers for the sensorless control of permanent magnet synchronous motors, an improved strategy combining a Fuzzy Adaptive Higher-order Sliding Mode Observer (HAFSMO) and a composite logarithmic sliding mode locked loop (EDS-PLL) is proposed. First, a higher-order adaptive sliding mode observer is designed, in which an exponential saturation smoothing function (ESSF) replaces the traditional sign function, and fuzzy control is employed to dynamically adjust the boundary layer parameters, enabling a smooth estimation and convergence of the back electromotive force within a finite time. Second, in the phase-locked loop stage, the exponential saturation smoothing function is integrated with the composite logarithmic sliding mode control to construct a composite logarithmic sliding mode phase-locked loop, further enhancing the accuracy of the rotor position observation. Finally, a simulation model was built on the MATLAB/Simulink platform for verification. Both the simulation and experimental results demonstrate that this method effectively suppresses system chattering and improves the accuracy of rotor position observation and overall system performance, thereby validating the effectiveness of the proposed sensorless control strategy.

This work presents a miniaturized dual-polarized endfire dielectric resonator antenna (DRA) array tailored for millimeter-wave (mmWave) 5G terminal systems. The proposed antenna element integrates a dielectric resonator with a cavity structure, both realized using standard printed circuit board (PCB) fabrication. Two orthogonal resonant modes of the DRA are excited to generate vertical (VP) and horizontal (HP) polarizations. To achieve broadband characteristics, two orthogonal cavity modes are further introduced and coupled with the DRA modes, enabling dual-mode operation. The VP and HP elements utilize an identical physical configuration, ensuring a highly compact architecture. Based on this unit, a four-element array was designed, fabricated, and experimentally verified. Measurements confirm an operational bandwidth of 26.1-29.8 GHz for both polarization states, with peak gains of 10.0 dBi and 10.1 dBi for VP and HP, respectively. Furthermore, both polarizations demonstrate beam-steering capability, indicating that the proposed dual-polarized endfire DRA array is a promising solution for next-generation 5G mmWave terminal applications.

Electromagnetic acoustic transducers (EMATs) have shown broad application prospects in industrial non-destructive testing due to their non-contact and couplant-free operation. However, their low energy conversion efficiency leads to a poor signal-to-noise ratio (SNR), especially under low-power excitation in safety-critical fields such as the petrochemical and nuclear power industries, thereby severely affecting thickness measurement accuracy. To address this challenge, this paper proposes an Adaptive Dual-Attention Fusion Autoencoder (ADFAE) for EMAT echo signal denoising. The ADFAE adopts a dual-path parallel architecture that integrates a multi-scale convolutional autoencoder with channel attention (MCACA) to capture local temporal features and a spatial attention-guided denoising autoencoder (SAGDA) to model global dependencies. Based on the denoised signals, a CNN-BiLSTM network is further employed to directly estimate material thickness. Experimental results demonstrate that the proposed method achieves effective denoising under low SNR conditions, with an average SNR improvement exceeding 23 dB and a mean Peak SNR above 43 dB. Compared with traditional time-of-flight (TOF)-based methods, the proposed ADFAE-CNN-BiLSTM framework significantly improves thickness measurement accuracy, reducing the average relative error to below 0.25%.

This article describe a linearly polarized lamp-shaped dual-wideband monopole wearable antenna for use in Industrial, Scientific and Medical (ISM), and public safety bands. To compress the antenna, the low current corners of the rectangular patch and the two regular octagons were eliminated. The lamp-shaped antenna of size 0.438λ₀ × 0.449λ₀ (53.9 × 55 × 1.0 mm³) was engraved on a jeans substrate at a frequency of 2.45 GHz. The antenna is 37.15% smaller (miniaturized) than a traditional rectangular patch antenna (59.7 mm × 78.68 mm) at the same design frequency. The antenna achieves dual widebands (2.17-2.86 GHz) and (4.42-5.06 GHz) with resonance frequencies of 2.45 and 4.70 GHz. At these resonant frequencies, the proposed wearable antenna has gain values of 3.86 dBi and 6.63 dBi and radiation efficiencies of 96.34% and 92.27%. Both the E- and H-planes exhibit bidirectional radiation characteristics. Thus, the proposed wearable antenna is the best for ISM, Wi-Fi, WLAN, Bluetooth, Wi-MAX (2.3 GHz), commercial, governmental, and military applications (4.40-4.99 GHz), hilly and watery rescue operations, radio astronomy services (4.80-4.94 GHz), public safety applications (4.94-4.99 GHz), Internet of Things (IoT), military fixed and mobile communications (4.40 to 4.50 GHz), and telemetry applications such as unmanned vehicles and drones. Finally the detailed electrical equivalent circuit modelling and ON-body and OFF-body Specific absorption Rate (SAR) investigations of the antenna are presented. The SAR values are found within the acceptable limits below 1.6 W/kg for 1g of tissue.

This paper presents the design, optimization, and experimental validation of a compact ultra-wideband (UWB) circular monopole antenna achieving a 3.05-23.04 GHz impedance bandwidth on a low-cost FR4 substrate (ε_r = 4.4, 0.8 mm thick, 30 × 20 mm²). The structure incorporates dual crescent-shaped slots and a defected ground structure (DGS) to enhance bandwidth and gain. The antenna was designed and optimized using ANSYS HFSS. Parametric optimization through four design steps demonstrated the impact of feed offset, slot incorporation, and ground-plane modification on impedance matching. The measured S₁₁ < -10 dB covered a UWB, spanning the sub-6 GHz, C, X, Ku, and K bands, with radiation efficiency of about 86% across the band. The antenna exhibited a peak gain of up to 6.6 dBi with nearly omnidirectional radiation at lower frequencies and more directive patterns at higher bands. Simulated and measured results validated the wideband performance and high radiation efficiency, and they agree within ±2 dB in gain in the band up to 18 GHz. The design enables cost-effective deployment in high-speed wireless data transmission, 5G, IoT, radar, and biomedical imaging applications.

A two-port coplanar waveguide (CPW) multi input multi output antenna (MIMOA) based on Koch Geometry (KG) with a wide bandwidth and high isolation is proposed in this work. A high frequency structure simulator (HFSS) is used for performance analysis and parametric optimization. Initially, a CPW-fed circular patch was designed, which was further modified using KG, and a single antenna element (SAE) was designed. A two port MIMO layout was further designed using the SAE. The proposed MIMOA is designed with Cross Slot on FR4 substrate, which offers a wide bandwidth of 1110 MHz (3.91-5.02 GHz) and works at 4.16 and 4.69 GHz. It exhibits excellent diversity performance with a Channel Capacity Loss (CCL) < 0.4 bits/s/Hz, Envelope Correlation Coefficient (ECC) < 0.25, Diversity Gain (DG) > 9.7, MEG (1,2) < 1 dB, Total Active Refection Coefficient (TARC) ≈ -20 dB from port 1 to port 2, and isolation of ≈ 20 dB across the band. The proposed MIMOA offers a high radiation efficiency (η) of ≥ 80% across the entire band. The designed MIMOA was fabricated and tested to validate the simulation results. Proposed MIMOA is useful for 5G communication and covers frequency ranging from 3.91 GHz to 5 GHz.

In this article, a novel ovate-shaped microstrip antenna (OMSA) is presented for application in wireless communication. It covers the evolution of a new shape and delves deeper into the resonance mechanism of the proposed design using characteristic mode analysis (CMA). The OMSA resonates at 2.45 GHz and 2.69 GHz with return loss of -18.82 dB and -31.84 dB, respectively. It offers a ultra-wideband performance with 91.46% measured bandwidth. The characteristic impedance and VSWR at 2.4 GHz are 49 Ω and 1.3, respectively. By introducing performance enhancement techniques such as ground truncation and a notch in the patch, the antenna resonance characteristics have been enhanced. A prototype of the proposed OMSA has been fabricated and validated experimentally. The time domain characteristics of the proposed OMSA have been simulated for both face-to-face (FtF) and side-by-side (SbS) configurations. The FtF configuration offers better performance, showcasing group delay of the OMSA < 2 ns and minimal variation along the operating band. The phase linearity is also maintained minimizing any distortions. The time domain results demonstrate a maximum fidelity factor of 90.62%, reaffirming the suitability of the antenna for wireless communication. The suitability of the proposed OMSA for wireless applications is also validated experimentally by analyzing group delay and S₂₁ phase linearity of the received signal.

This paper presents a comparison between jeans and FR4 based patch antenna sensors for blood glucose sensing using a non-invasive approach. The dual-feed square-patch antenna sensor with partial ground has a compact structure operating at 2.8 GHz frequency. The performance of the antenna sensor was evaluated by measuring the shifts in resonant frequency with varying blood glucose concentration in the simulation. Both antenna sensors were experimentally tested and validated by placing a human volunteer's fingertip on the patch. The jeans-based antenna sensor exhibited higher sensitivity to glucose variation than the FR4 based antenna. This study demonstrates the crucial role of substrates in sensing applications involving interactions with human tissues.

Based on the time-dependent Schrӧdinger equation, a finite-difference time-domain (FDTD) method is proposed to investigate electron propagation with the presence of tunneling potential distributions in metal-oxide-semiconductor field-effect transistors (MOSFETs). The channel current equation in the drift-diffusion model for classical transport is derived from the probability current formula with a plane wave assumption of the electron's state function. In both classical and quantum regimes, channel currents are numerically simulated based on quantum transport in MOSFETs using transmission functions and Fermi-Dirac distributions. The transmission function is obtained from the non-equilibrium Green's function (NEGF), indicating the probability of electrons through a channel. To determine the number of electrons at both source and drain terminals of a MOSFET, the Fermi-Dirac distributions are calculated. Numerical simulations of channel currents with various external gate-source and drain-source voltages are investigated, showing that a similar peak channel current can be generated with lower external voltages in a smaller MOSFET with a shorter gate length. Electron forward and backward propagations are obtained through FDTD simulations to demonstrate the difference of cutoff modes in classical and quantum MOSFETs.

Achieving simultaneous wideband operation and high output power efficiency remains a major challenge in modern GaN HEMT power amplifier (PA) design, particularly for broadband communications and radar systems. This paper presents a systematic design methodology for a broadband PA that integrates radial-stub (RS)-based bias/matching networks with an algorithmic gate-bias (V_GS) optimization, alongside load-pull-derived device termination and compact layout. Starting with theWolfspeed CMPA0530002S GaN HEMT, which features intrinsic broadband stability and an integrated input match, we replace conventional narrowband bias lines with a radial-stub network that ensures broadband bias isolation and low-loss matching. A thorough load-pull study identifies the optimum load impedance for concurrent maximization of power-added efficiency (PAE), gain, and output power. Subsequently, an automated V_GS sweep across the full 1.16-1.6 GHz band determines the optimal bias point for broadband and efficiency trade-off. The PA achieves a simulated result of output power of 34.28 dBm , flat gain of approximately 13.28 dB, and a peak PAE of 58.69% in a fractional bandwidth of 37% (1.16-1.6 GHz). A key novelty of this work lies in the proposed algorithmic V_GS sweep technique, which enables optimization of broadband efficiency throughout the entire 1.16-1.6 GHz operating band and can be easily extended to other frequency ranges. Unlike conventional bias optimization methods that are limited to a single frequency, the proposed algorithm systematically identifies the optimal gate bias across multiple frequencies to maintain high efficiency and consistent output power over a wide bandwidth. The simulated results confirm that this algorithmic bias optimization approach achieves superior broadband efficiency and stable output performance, providing a scalable and adaptable design methodology for next-generation wireless communication and electronic warfare systems.

This paper presents a compact four-port conformal multiple-input multiple-output (MIMO) antenna designed on a 0.1-mm-thick transparent flexible polyimide substrate for wideband X-band wireless applications. Each antenna element is composed of an annular ring radiator and an asymmetric coplanar ground to achieve low mutual coupling and high diversity performance. The proposed MIMO antenna covers an impedance bandwidth of 7.9-14 GHz, with isolation greater than 20 dB and a maximum reflection coefficient of 32.5 dB at 10.5 GHz. The experimental results are in good agreement with the simulated results in terms of reflection, transmission, and radiation characteristics. The measured gain ranges from 4.5 to 6 dBi, with stable radiation patterns across the operating band. The MIMO performance metrics, including the envelope correlation coefficient (ECC = 0.002), diversity gain (≈10 dB), channel capacity loss (<0.3 bits/s/Hz), and total active reflection coefficient (TARC), confirm the suitability of the design for robust high-data-rate communication. Furthermore, the antenna maintains stable operation under various bending configurations, ensuring its potential for X-band conformal and wearable applications.

This paper describes a Pseudo-Noise (PN) sequence evaluation tool that analyzes potentially corrupted PN sequences and assigns a metric score indicating the quality of the received sequence. The PN tester is designed to support Spread Spectrum Time Domain Reflectometry (SSTDR) by evaluating reflected PN sequences and determining whether the received signal is valid or too corrupted for use. Signal degradation is influenced by noise levels and channel filters encountered by the sequence. To simulate real-world conditions, various types of noise and filtering effects - representing capacitive or inductive coupling - were applied to a maximum-length PN sequence. The evaluation model demonstrated a consistent decline in correlation as signal distortion increased, confirming its effectiveness in assessing signal quality.