This paper proposes a four-mode circularly polarized metasurface multiple-input multiple-output (MIMO) antenna based on characteristic mode analysis (CMA), which can be applied to Sub-6GHz communications, unmanned aerial vehicle communications, wireless local area network, and other scenarios. Its core geometric novelty is a gradient-scaled 4×4 metasurface radiating layer: central units with corner truncation and 45° rotated rectangular stubs, and four corner units scaled down to 0.75 times the central size. This structure generates the 90° phase difference for CP radiation, synchronously exciting two orthogonal characteristic mode pairs to realize broadband CP radiation, and endows the metasurface with inherent self-decoupling capability. In addition, a 2×2 MIMO array is constructed by combining four monopole antenna elements, and the mutual coupling is suppressed by the metasurface itself, achieving a port isolation greater than 25 dB. Simulation and measurement results show that the impedance bandwidth is 41.93% (5.07-7.76 GHz), the axial ratio (AR) bandwidth is 17.5% (5.37-6.40 GHz), the peak gain is 6.77 dBi, the array envelope correlation coefficient is as low as 0.0002, and the diversity gain reaches 9.999 dB. The antenna achieves an excellent balance among broadband performance, high isolation, and structural simplicity, outperforming existing similar designs.

In this paper, a novel diplexing power divider with a lowpass and two bandpass channels is presented. The lowpass channel is constructed by using a 7th-order quasi-elliptical transfer function, while the dual-band bandpass response is obtained by using co-directional split ring resonators. A lowpass-bandpass diplexer is first designed by integrating the lowpass and bandpass filters directly. In order to achieve the power division within the entire frequency range, a multi-section power divider is located at the end of both filter structures. The proposed lowpass-bandpass diplexing power divider is fabricated and measured in very good agreement with the predicted results. The measured frequency range of the lowpass channel is between 100 MHz and 2 GHz. The measured center frequencies of the bandpass channels are at 3.4 and 3.9 GHz with the 3-dB fractional bandwidths of 7 and 6.6%, respectively.

This paper presents a tri-split ring resonator (TSRR) integrated with a rectangular dielectric resonator antenna (RDRA) using an E-shaped microstrip feed line. The RDRA, measuring 15×14×14 mm³ and constructed on an FR4 substrate of 46×46×1.6 mm³, features a gain of 10.9 dBi and a fractional bandwidth of 22.05% (5.85 GHz-7.3 GHz) with radiation efficiency over 82%. It supports fundamental modes TE₁₁₁ at 6.12 GHz, along with lower- and higher-order modes TE_1δ2 at 6.13 GHz, TE_3δ3 at 6.14 GHz, and TE₃₃₃ at 6.2 GHz. Simulated and measured results show close agreement across the operating band. The proposed antenna has several applications, including point-to-point microwave links (5.925 GHz-7.125 GHz), satellite communication in the C-band, and defense and military communication.

A compact, double split-ring H-shaped resonator-based polarization-independent dual-band metamaterial microwave absorber (MMA) with an outstanding absorption efficiency was designed and analyzed for satellite communication applications. The H-shaped resonator-based unit cell was printed on an FR4 material using copper as the conducting material. Copper material was chosen for the radiating patch and the ground plane. A detailed parametric analysis was performed by tuning the geometrical parameters of the H-shaped MMA to achieve dual absorption bands with broad bandwidth and high absorptivity. The recommended H-shaped absorber exhibits dual absorption bandwidths of 710 MHz and 1630 MHz with FBW of 22.95% and 19.35%. Furthermore, it maintains an absorptivity of greater than 90% across the entire spectrum of dual operating bands with almost perfect absorption of 99.99% at the resonant frequencies (3.17 GHz, 7.78 GHz) of each band. The MMA maintains an area of 0.09λ × 0.09λ. A simulated absorber model was fabricated, and the results have been tested using an Anritsu Combinational Analyzer (MS2037C) for experimental validation. The simulated and tested outcomes of the developed prototype are in strong alignment, rendering the absorber suitable for S-band and LEO and geostationary satellite uplinks/downlinks, with specific bands often at 7.145-7.235 GHz (uplink) and 8.4-8.5 GHz (downlink).

A compact, low-profile, and highly isolated four-element flexible MIMO antenna for biomedical body-centric wireless applications is proposed and experimentally validated. The antenna is realized on a 75 × 75 × 1 mm³ ultra-low permittivity felt substrate (ε_r = 1.2, tanδ = 0.0013) and incorporates a perturbed circular slot with rectangular defected ground stubs to simultaneously enhance impedance bandwidth and inter-element isolation. The proposed design achieves a measured -10 dB impedance bandwidth of 320 MHz (2.20-2.52 GHz), corresponding to a fractional bandwidth of 13.3% centered at 2.4 GHz ISM band. The four-element MIMO configuration exhibits isolation better than 25 dB despite an edge-to-edge spacing of only 1 mm, demonstrating strong mutual coupling suppression without additional decoupling structures. The antenna provides a peak gain of 2.8 dBi and achieves a peak radiation efficiency of 95%, with an efficiency of 92.5% under flat conditions (R = 0 mm). Envelope correlation coefficient (ECC) remains below 0.01, ensuring excellent diversity performance. Under conformal bending conditions (R = 10-60 mm), the antenna maintains stable resonance with only 1.6% frequency deviation, while gain and efficiency remain above 2.21 dBi and 84.58%, respectively, demonstrating robust mechanical resilience. On-body evaluations over arm, leg, and chest phantoms indicate stable operation within 2.35-2.49 GHz, with gain varying between 1.87-2.01 dBi and efficiency above 87.15%. The maximum measured SAR is 5.98 W/kg (1 g tissue), confirming acceptable safety compliance for wearable biomedical applications. Measured S-parameters and radiation patterns show strong agreement with simulations, validating the proposed slot-ground co-engineering methodology. Compared to existing wearable ISM antennas, the proposed design offers isolation >25 dB, high efficiency (95%), mechanical flexibility, and compact form factor without requiring complex EBG or AMC structures. The antenna is therefore a strong candidate for next-generation flexible biomedical MIMO systems.

In this letter, a series of high-selectivity bandpass filters based on parallel-coupled microstrip lines are proposed. The developed filters are derived from conventional parallel-coupled microstrip line filter, with an additional pair of parallel-coupled microstrip lines being incorporated into the two open ends, one end of which is short-circuited. Accordingly, a pair of transmission zeros is introduced into the transmission coefficient of the traditional parallel-coupled microstrip line filter by this modification, thereby enhancing its selectivity. Additionally, to further enhance the selectivity of the developed filter, a pair of quarter-wavelength transmission lines are connected to each of the short-circuited ends. This additional structure introduces another pair of transmission zeros, thereby further improving the selectivity of the developed filter. For demonstration, two bandpass filters have been designed and fabricated. Specifically, measured attenuation slopes for the modified structure were 213 dB/GHz and 106 dB/GHz at the lower ND upper band edges, respectively.

To address the demand for broadband, high-gain antennas in millimeter-wave communications, this paper proposes a stacked dipole patch array antenna based on substrate integrated waveguide (SIW) technology. The design employs a three-layer structure with slot-coupled feeding to enhance radiation performance. First, an SIW feeding structure is integrated into the bottom layer to ensure efficient signal coupling. Second, the middle layer features an innovatively designed ``wrench-shaped'' patch with metal vias, which not only effectively broadens the bandwidth but also enhances gain in conjunction with the rectangular patches on both sides. Finally, rectangular dipole patches are introduced in the top layer as parasitic elements to further optimize high-frequency performance. Through a 1-to-4 corporate-feed power divider network, the antenna achieves a measured impedance bandwidth of 24.42% (24.12 GHz-30.83 GHz) and a center frequency gain of 11.02 dBi. While achieving miniaturization, this antenna combines high bandwidth with high gain, demonstrating its application potential in next-generation millimeter-wave wireless communication.

This paper proposes a spoof surface plasmon polariton (SSPP) based on a coplanar waveguide (CPW) with an interdigital structure, aiming to realize a plasmonic filter with both miniaturization and sharp transition characteristics. Dispersion and transition analyses demonstrate that the proposed unit exhibits flexibly controllable dispersion and transition features by tuning the geometrical parameters of the interdigital unit. Based on this, a compact filter with the proposed structure was designed, simulated, and experimentally validated. The introduction of the interdigital slot structure provides an additional degree of freedom for tuning, enabling the filter to achieve a steep transition from the passband to the stopband (with a roll-off rate of up to 181.31 dB/GHz) while maintaining a compact size. The measured results are in good agreement with the simulated ones, which verifies the effectiveness of the proposed design. In addition, the bandpass response introduced by higher-order modes offers a feasible route toward the multimode and multifunction integration of filters.

Objective: To enable direct joint prediction of tumor center coordinates and radius in non-imaging ultra-wideband (UWB) breast sensing, we propose an edge-fusion-based graph attention framework for learning from multi-channel backscattered signals without the need for image reconstruction. Methods: Breast models were generated using finite-difference time-domain (FDTD) simulations. Backscattered signals were preprocessed using the dual-tree complex wavelet transform (DTCWT). UWB measurement channels were reformulated as a graph, where each transmitter-receiver channel was treated as a node, and edges were defined by shared antennas. Edge features were fused into graph attention message passing to emphasize more tumor-relevant channels, followed by a multi-task regression head to predict tumor center coordinates and radius. Results: Across four breast density categories, mean center localization error (CLE) remained below 2.5 mm, and the mean of comprehensive overlap index (COI), area recall ratio (ARR), and area precision ratio (APR) exceeded 0.50 in all models. These results indicate effective joint localization and size estimation across heterogeneous breast models.

Megahertz wireless power transfer (MHz-WPT) enables compact resonant components; yet the matching, compensation, and filtering stages used in conventional systems can dominate loss and standby dissipation at MHz operation. To address this issue, this work proposes a compact 13.56 MHz WPT architecture in which impedance transformation is integrated into the resonant hardware. A self-resonant transmitting coil is co-designed with a Class-E power amplifier to shape the reflected load toward the optimum operating condition, thereby removing the external compensation network, the additional matching stage, and the lumped-element LC output filter. The analysis shows that, when the receiver is removed, the effective load becomes dominated by the transmitter resistance, inherently suppressing delivered power without sensing or closed-loop control. A prototype delivers 9 W over 30 mm with 81.5% end-to-end DC–DC efficiency, while under receiver absence, the DC input power decreases from 11 W to 1.15 W. These results demonstrate a simplified and robust MHz-WPT architecture with reduced component count and inherently low standby dissipation.

This study presents a novel double-sided axe-shaped antenna with a triple band for multibandcst applications. The presented antenna features a circular ring and two ring sectors as a double-sided axe-shaped patch antenna to generate three resonant frequencies, WiMAX 3.55 GHz (3.5-3.62 GHz), WLAN 5.12 GHz (5-5.28 GHz), and X-band 7.67 GHz (7.18-8.17 GHz), with reflection coefficients of -14.86 dB, -19.36 dB, and -36.96 dB, respectively. The proposed antenna is fabricated on an FR4 (ε_r = 4.3) substrate with dimensions of 30 × 30 × 1.6 mm³ and uses DGS ground to improve the current distribution and impedance bandwidth. The proposed antenna is successfully simulated and measured. The performance evaluation of the multi-band antenna demonstrated satisfactory agreement between simulations and measurements. The proposed multi-band antenna combines enhanced performance with a compact size.

This paper presents a compact wideband integrated filtering antenna for X-band applications enabled by a three-dimensional (3D) vertical-interconnect architecture. A self-packaged electromagnetic platform is constructed on a multilayer substrate with a central air cavity, realizing high-density monolithic integration of a slotted patch radiator and a seventh-order microstrip bandpass filter (BPF). Distinct from conventional planar cascaded filtering antennas, the proposed 3D collaborative electromagnetic structure - formed by the air cavity, a perimeter vertical interconnect access (VIA) array, and multilayer ground planes - provides low-loss signal transmission and effectively suppresses parasitic coupling within a compact volume. To enhance radiation performance, the patch is co-optimized via slot loading, chamfering, and asymmetric feeding to extend the surface-current path, lower the resonant frequency, and broaden the impedance bandwidth, achieving a 45.27% reduction in patch area relative to the initial design. To accommodate the BPF within the packaging boundary, spatial adaptation and impedance matching are achieved through a tilted layout, arc-shaped port extension, and vertical feed VIAs while maintaining essentially unchanged electrical performance. Measured results demonstrate a 40.3% fractional bandwidth from 7.99 to 12.02 GHz, a peak gain of 6.85 dBi, good out-of-band/harmonic suppression, and stable radiation patterns. The overall size is 1.17λ₀ × 1.17λ₀ × 0.12λ₀. The proposed 3D vertical-interconnect and multifunctional self-packaged co-design methodology offers an effective solution for broadband, miniaturized, high-isolation filtering antennas and system-on-package (SoP) RF front ends.

Synthesizing large arrays composed of irregular clustered subarrays is a research approach of increasing attention from researchers. In this article, an irregular clustered subarray tiling strategy based on different polygonal shapes as a mask partitioning with a convex optimization algorithm (COA) is proposed. A set of polygon partitioning was proposed by formulating a problem of tiling an array of irregular subarrays to make it suitable for any aperture grid. To further reduce the complexity of the systems and accelerate the execution time of the responsible algorithm, amplitude-only feeding was considered. In all proposed partitioning scenarios, only 16 polygonal clusters (i.e., complexity of 1.7%) were synthesized, achieving high-constrained radiation performance targets of reducing sidelobe level (SLL) to -45 dB and generating a 6-degree wide and -180 dB deep null steering with the ability to orient the main beam as required. Polygonal clusters of varying sizes, shapes, and side counts were synthesized, ranging from a 3-sided polygon (i.e., a triangle) to a 10-sided polygon (i.e., a decagon). Based on this, six polygonal segmentation configurations were proposed, resulting in a high-performance electromagnetic beam pattern (BP). Computer simulation results demonstrated the robustness and effectiveness of the proposed scenarios in meeting the performance constraints imposed on the optimization algorithm. The good performance and potential inherent in the methods presented in this paper were verified by comparing them extensively with current methods in various numerical examples.

This paper presents the design of compact multi-band filtered MIMO antenna whereby the UWB antenna is converted into tri-band antenna by adding two stubs-loaded band-notch filters (SLBNFs). The notch structures tactfully quiet undesired frequency bands and permit three clean operating bands likely to be utilized in S-band and C-band wireless systems. A 2 × 2 MIMO system is proposed using a centrally located decoupling network to regulate the distribution of surface currents, which achieves over 25 dB of isolation in all operating bands. The fractional bandwidth of the antenna in the first band (2.0-2.6 GHz), second band (3.48-3.82 GHz), and third band (5.68-6.42 GHz) are 16%, 9.3%, and 12.23%, respectively. The peak gains in the corresponding operating bands are 2.8 dB, 4.1 dB, and 5 dB, respectively. The proposed design is suitable for the present-day S- and C-band communication systems and multi-standard wireless devices due to its selective multi-band response, better isolation, and compact structure.

This study presents a compact patch antenna in the form of a circle, suitable for use in medical and wearable Internet of Things (IoT) devices. The recommended antenna has been proposed to operate on a polyamide material with a dielectric constant of 3.5 and loss tangent of 0.008, at 2.4 GHz and 5.8 GHz bands. The IoT wearable antenna has a specific absorption rate (SAR) obtained at 2.4 GHz that is 0.6 W/kg, while at 5.8 GHz it is 0.8 W/kg for 1 g of body tissue. Both values are significantly below the Federal Communications Commission (FCC) exposure limit, confirming the safe operation of the compact IoT-enabled wearable antenna. The antenna achieves simulated gains of 7.54 dBi and 7.96 dBi with radiation efficiencies of 85.45% and 87.55% at 2.4 GHz and 5.8 GHz, respectively. The proposed system integrates the proposed antenna with an ESP8266 microcontroller, which enables the transmission of vital signs data over an IoT platform. A Modbus protocol and Node-RED platform are utilized for data acquisition, processing, and visualization. This makes it a small, cheap, and reliable solution for IoT-enabled healthcare systems.

In this study, a novel symmetrical complementary double-split-ring resonator structure is proposed, operating in the frequency bands of 2.39-2.44 GHz (covering the core 2.4 GHz WLAN band) and 3.45-3.60 GHz (covering a key sub-band of n78 for 5G communications), to reduce the coupling of multiple-input multiple-output (MIMO) antennas within these two frequency bands. To align with the trend of antenna miniaturization, the inter-element spacing is only 0.08λ₀. The measured results show that after loading the metamaterial, the antenna coupling in the operating bands is reduced by 0-10 dB and 8-23 dB, respectively, and the coupling in the two bands is below -17 dB and -27 dB, respectively. The peak gains achieved are 3.12 dBi and 4.51 dBi in the two bands. The ECC is less than 0.02, indicating excellent gain performance and effective decoupling capability of the MIMO antenna.

This paper proposes a compact UWB MIMO antenna with band-notched characteristics and high isolation. With a miniaturized footprint of 60 × 32 mm, the antenna covers the full UWB spectrum of 3.1-13 GHz. A core structural innovation lies in the design of a novel SRR metamaterial unit, which exhibits superior high-frequency decoupling capability by regulating electromagnetic wave propagation; combined with the synergistic decoupling mechanism of a meandered-line radiating patch and an I-shaped DGS for low-frequency isolation enhancement, the antenna achieves an excellent measured isolation (S₂₁) of better than -21 dB across the entire operating band. Additionally, four precise notched bands (3.3-3.4 GHz WiMAX, 4.4-5.0 GHz n79, 5.15-5.825 GHz WLAN, 7.9-8.4 GHz) are realized via strategically etched slots on radiating elements to suppress interference. Verified by measurements, the measured ECC is as low as below 0.018, and the diversity gain maintains stability near the ideal 10 dBi. The antenna exhibits stable radiation patterns throughout the impedance bandwidth, accompanied by outstanding diversity performance.

A novel wide-stopband filtering power divider (FPD) is proposed in this paper. The proposed wide stopband FPD integrates a pair of three-line coupled structures (TLCSs)-based bandpass filters (BPFs) and stepped-impedance open stubs. This topology achieves a wide stopband through harmonic suppression and enhanced filtering simultaneously. Specifically, the stepped-impedance open stubs effectively suppress harmonics to extend the stopband while also improving in-band impedance matching. Concurrently, the TLCS-based BPFs generate multiple transmission zeros (TZs) on both sides of the passband, improving frequency selectivity. A prototype wide stopband FPD operating at 3.5 GHz is fabricated and measured. There is a favorable agreement between the measured and simulated results, displaying a stopband up to 15 GHz (4.3f₀), which features a rejection level of -15.8 dB and -10 dB fractional bandwidths of 44.8%.

In addition to considering the electromagnetic performance of the motor itself, the optimal design of an onboard permanent magnet synchronous motor (PMSM) must also account for its compatibility with a vehicle and the impact of driving cycles. To address this problem, in this study, we propose a nested optimization design approach for PMSMs to achieve an optimal rotor design for vehicular applications. First, Morris sensitivity analysis is employed to classify the parameters to be optimized into highly and generally sensitive parameters. Subsequently, the Kriging model and NSGA-III algorithm are successively applied to perform hierarchical optimization for the highly sensitive parameters, followed by the generally sensitive parameters. To select the motor structure that best adapts to the vehicle and driving cycle, the efficiency maps of candidate solutions are solved and nested into the vehicle energy management model for optimization. The results demonstrate that the proposed method enables the identification of PMSM structures on the Pareto front that better match the vehicle and driving cycle. Compared with other high-performance solutions, the final optimal point achieves fuel consumption savings of up to 19.1%.

This study designs and experimentally validates a digitally controlled 2.45 GHz solid-state microwave power source for industrial continuous-wave operation. The source employs a cascaded laterally diffused metal oxide semiconductor (LDMOS) architecture integrating a phase-locked loop frequency synthesizer, a multi-stage driver chain, and a closed-loop digital power-control network with 0.5-dB resolution. The final-stage power amplifier (PA) is biased in deep class-AB, and a lumped-element matching network is synthesized - guided by load-pull and harmonic-impedance analysis - to realize a near-short termination at the second harmonic and reduce voltage-current overlap energy. Nonlinear device modelling and system-level analysis are used to predict efficiency and stability. Measurements show a saturated output power of 54.09 dBm, gain of 18.14 dB, and peak power-added efficiency of 61.89% under a 28-V supply. The source achieves accurate continuous-wave (CW) power regulation from 35 to 53 dBm with good thermal stability. These results indicate that combining deep class-AB biasing with second-harmonic near-short termination enables high-efficiency operation in L/S-band industrial microwave sources, and the cascaded digitally controlled architecture provides robust power management for microwave heating and plasma excitation systems.