This paper describes the design methodology of a compact multiband microstrip patch antenna intended for next-generation wireless communication applications. The proposed antenna operates over seven distinct frequency bands: 1.25-1.32 GHz, 2.30-2.44 GHz, 2.50-2.75 GHz, 2.92-3.25 GHz, 3.40-3.65 GHz, 3.70-4.23 GHz, and 4.70-6.0 GHz. These operating bands support a wide range of wireless services, including LTE, 5G communications, Wi-MAX, ISM applications, radar systems, and broadband wireless communications. Multiband performance is achieved through the incorporation of three strategically placed slits in the radiating patch along with a square split-ring resonator (SSRR). By adjusting the dimensions of the slits and the position of the SSRR, the operating frequency bands can be effectively tuned. The proposed antenna occupies a compact footprint of 40 × 40 mm² and consists of a radiating patch, a partial ground plane, and an SSRR structure. Simulation results demonstrate resonant frequencies at 1.3, 2.38, 2.66, 3.0, 3.5, 4.2, 4.9, and 5.7 GHz. Owing to its compact size, multiband capability, and simple structure, the proposed antenna offers advantages in terms of reduced cost, lower system complexity, and miniaturization, making it suitable for modern wireless communication systems.

Due to the high electrical conductivity, relative permittivity, and magnetic permeability of seawater, the propagation behavior of electromagnetic fields differs significantly from that in air. The conductive nature of seawater causes strong eddy current loss and magnetic field attenuation, thereby reducing the effective coupling coefficient and resulting in frequency detuning between the transmitter and receiver coils. Moreover, the marine environment introduces parasitic impedance paths and additional energy dissipation due to the conductive medium, which further decreases transmission efficiency. These unique electromagnetic characteristics make the design and optimization of wireless power transfer (WPT) systems in seawater more complex and challenging than in air, motivating this study to develop and analyze a dual-receiver WPT architecture that improves midrange transmission efficiency under underwater conditions. To address this issue, a single-transmitter dual-receiver (1TX-2RX) WPT system operating in the 300-550 kHz frequency range is designed and implemented. Experimental results demonstrate that, under midrange transmission in seawater, the efficiency of the proposed 2RX architecture improves markedly from 12% in the 1RX system to 25%, while maintaining stable output performance under various receiver coil misalignment conditions. In addition, compared with operation in air, the optimal operating frequency of the 2RX system in seawater shifts leftward from approximately 460 kHz to 410 kHz. To better characterize the impact of seawater on transmission performance, complex impedance and mutual inductance parameters are incorporated into the conventional circuit model, enabling effective representation of the additional losses and coupling attenuation induced by the conductive medium. The predicted load voltage is consistent largely with the experimental measurements, validating the accuracy and applicability of the proposed modeling approach. Overall, this study not only verifies experimentally the feasibility of improving midrange transmission efficiency through a dual-receiver architecture but also establishes theoretically a circuit modeling method suited better for seawater environments, providing useful insights for the design and optimization of marine WPT systems.

Interrupted Sampling Repeater Jamming (ISRJ) is a typical intra-pulse coherent deceptive interference that poses a serious threat to radar target detection and tracking performance. This paper proposes an anti-jamming method that integrates a dual-modulated SSFA-MCPC waveform with a segmented mismatched filtering scheme. Based on the multi-carrier phase-coded (MCPC) signal, we apply random sub-pulse frequency agility and chaotic time-domain phase coding to design the SSFA-MCPC waveform. This design enhances the distinction between the radar signal and interference and improves the mutual masking among sub-pulses. To counter ISRJ, a segmented mismatched filtering algorithm is proposed. Specifically, a bank of sub-pulse matched filters is constructed to perform segmented pulse compression on the received echoes, and the Otsu algorithm is employed to adaptively identify jammed sub-pulses. Finally, a reconstructed mismatched filter is applied to suppress interference. Simulation results demonstrate that the proposed method does not rely on prior knowledge of the jamming parameters and can effectively suppress ISRJ under three different forwarding modes. Compared with existing methods, the proposed approach has lower computational complexity and shows strong potential for practical engineering applications.

The Fifth-Generation (5G) radio network consists of two spectrums: one millimeter-wave band (24-40 GHz) and the other below 6 GHz, which is also popularised as sub-6 GHz band. The spectrum of a sub-6 GHz radio network may be divided into three bands, i.e., low-band (below 1 GHz), mid-band (1-2.6 GHz), and upper mid-band (3.5-6 GHz). The low-band provides a good network coverage, and the mid-band offers a balance between coverage and capacity, whereas the high-band provides the super data capacity and speed. The service providers use combinations of different bands from these three segments of sub-6 GHz spectrum to deliver smooth 5G services. In this work, a novel design of a multiband Double Sided Printed Dipole Antenna (DSPDA) system is proposed that operates at least at one band in each segment of the sub-6 GHz spectrum. The design consists of two DSPDAs, a symmetric one and an asymmetric one, fed in series by a common line in a tree-like structure. The multiple bands are obtained by having fundamental resonant frequencies and their harmonics. All bands are predictable by the design equations. It also provides the flexibility of choosing any band of operation. The antenna is experimentally verified.

This comment addresses errors in the explicit expressions of the Ω matrix presented by Blankenship et al. (2025) [1]. We show that sign inconsistencies in the original formulation can lead to non-physical results, including the violation of energy conservation in passive lossless environments. We provide corrected formulas for the affected matrix entries and numerically verify that the corrected formulation restores physical consistency, with the total energy conserved to the displayed precision in the lossless benchmark.

This research paper presents a low-profile ultra-wideband (UWB) multiple-input multiple-output (MIMO) antenna with enhanced isolation and wideband performance, employing polyimide as the substrate. The suggested configuration consists of two symmetric radiating elements incorporating rectangular and circular slots within a compact footprint of 36 × 21.1 × 0.1 mm³. To effectively suppress mutual coupling, a slot-based metamaterial-inspired defected ground structure (DGS) with a meandered profile is introduced between the antenna elements. In addition, inverted U-shaped stubs and optimally placed slots are integrated to form a stub-loaded decoupling network, further improving inter-element isolation across the UWB spectrum. The antenna exhibits resonant modes at 4.16 GHz (WLAN), 5.49 GHz (IoT and smart home applications), 7.54 GHz (satellite and point-to-point communications), and 11.61 GHz (high-resolution imaging and sensing), covering the 4-12 GHz frequency range. Predicted and tested outcomes present good agreement, with key MIMO performance parameters achieving Channel Capacity Loss (CCL) below 0.4 bits/s/Hz, diversity gain (DG) above 9.9 dB, Envelope Correlation Coefficient (ECC) below 0.005, and Total Active Reflection Coefficient (TARC) less than -10 dB. Owing to its compact size, wideband operation, and high isolation characteristics, the suggested antenna is a strong candidate for wireless area networks and emerging IoT-based sensing applications.

A direct-through three-level inverter topology based on center-tap inductance and its complex vector control strategy are proposed. This topology structurally avoids the direct short-circuit problem of the DC side capacitor, eliminates the need to set a dead zone in the drive signal, and eliminates the low-order harmonics introduced by the dead zone. For this direct-through inverter, the corresponding complex vector control strategy is studied. By establishing a full-frequency domain model of the system, the fundamental cause of the coupling of DQ-axis currents in the synchronous rotating coordinate system was analyzed. To address the issue of poor dynamic response caused by coupling, a complex coefficient controller was designed. By introducing imaginary parts into the controller parameters, the additional poles introduced by coordinate transformation were offset, achieving decoupling control of active and reactive currents.Simulation and experimental results show that, compared with the traditional real-coefficient PI controller, the proposed complex vector control strategy can effectively reduce the coupling degree of DQ-axis current, improve the dynamic performance of the system, and verify the correctness and effectiveness of the proposed topology and control method. This inverter topology features both high reliability and excellent output performance without increasing the number of power switch devices.

This paper proposes a dual-band class-F^-1 high-efficiency power amplifier with an integrated structure for harmonic suppression and fundamental matching. The fundamental matching network employed a dual-frequency coupler with open branches. This structure is partially reused for third-harmonic control by leveraging two open branches and two branch lines. By adjusting the characteristic impedance of the quarter-wavelength transmission line, the third-harmonic impedance is adjusted to a short circuit at both fundamental frequencies at the drain of the power amplifier. The second-harmonic control network consists of a quarter-wavelength open stub and a drain bias line loaded with a double spiral defected ground structure (DGS), which controls the second-harmonic impedance to an open circuit state at the drain, satisfying the class F^-1 harmonic conditions. A dual-band high-efficiency class F^-1 power amplifier operating at 2.6 GHz/3.4 GHz is designed and fabricated. The measured results show drain efficiencies of 73.5% and 74.3% at 2.6 GHz/3.4 GHz, with output power exceeding 40 dBm and gain above 10 dB.

Wide-stopband plasmonic filters are essential components in compact mid-infrared (MIR) photonic systems. This work proposes a geometrically tunable wide-stopband plasmonic filter based on a metal-insulator-metal (MIM) waveguide with dual resonator cavities. The optical response is numerically investigated using the two-dimensional finite-difference time-domain (2D FDTD) method. The influence of the resonator height H₂ and the inter-cavity distance D on the stopband characteristics is analyzed. The symmetric dual-cavity configuration enables effective control of the stopband bandwidth and central wavelength. The design achieves a significantly broadened stopband while maintaining compactness and high transmission selectivity, making it a promising candidate for integration into mid-infrared photonic and sensing systems.

CO₂ conversion is a central strategy for closing the carbon cycle and enabling sustain- able energy and chemical production through catalytic pathways. In this work, a descriptor-based, data-driven computational framework is employed to screen nanocatalysts for CO₂ conversion using density functional theory data reported in the literature. Key adsorption and electronic descriptors, including CO₂∗ and CO∗ binding energies, are analyzed to establish structure-activity relationships governing catalytic performance. Correlation and volcano-type analyses reveal that moderate adsorption strengths are essential for balancing CO₂ activation and product desorption, while excessively strong binding leads to surface poisoning and reduced activity. The results demonstrate that descriptor-guided screening can effectively rank catalyst candidates and provide rational design rules, without relying on new computationally intensive simulations. This framework offers a computationally efficient pathway for accelerating nanocatalyst discovery for CO₂ conversion.

To address the challenge of achieving both steady-state accuracy and fast dynamic response in permanent magnet synchronous motor (PMSM) systems equipped with LCL filters, this paper proposes a complex vector PI controller optimization method. The proposed approach extends the conventional real-axis PI control to the complex domain, enabling unified modeling of current decoupling and harmonic suppression. Based on this formulation, the response surface methodology (RSM) is employed to optimize the controller parameters. A quadratic response model is established through design of experiments (DOE), with steady-state error, dynamic overshoot, and harmonic suppression indices defined as optimization objectives to obtain the optimal parameter set. The core contribution of this work is the integration of a frequency-domain complex-vector model with a systematic multi-objective optimization framework using Response Surface Methodology (RSM) and Generalized Reduced Gradient (GRG) algorithms. This approach addresses the inherent coupling and resonance issues in LCL-filtered PMSM systems. Quantitative experimental results demonstrate that, compared with conventional tuning methods, the proposed strategy reduces the current settling time by 47.6% and suppresses torque overshoot by 92.8%, thereby achieving a superior balance between fast transient response and steady-state accuracy.

In this paper, an elliptical monopole antenna is modified and loaded with stubs and slots to improve filtering characteristics over tri-band operation. As the surface current is concentrated at the periphery of the monopole and decreases away from the feed, therefore, a slotted elliptical monopole is designed and sliced from the top. A rectangular strip is added at the top and center to create two symmetrical loops. A slot in each loop at a different position causes the antenna to operate over dual/tri-bands. A rectangular stub is added in the feed-line to improve the band-stop/filtering characteristics. The parameters of the structure are optimized to obtain S₁₁ ≤ -10 dB over 3.22-3.64 GHz, 5.53-6.03 GHz and 6.71-7.14 GHz for 5G, V2X, WLAN and Wi-Fi 6E applications. The three bands can be tuned independently. The compact 0.171λ₀ × 0.184λ₀ antenna, fabricated on 1.6 mm FR4 substrate (λ₀ is the free-space wavelength at 3.22 GHz), offers maximum S₁₁ of -0.9 dB and -4.9 dB, respectively, between the lower and middle bands and middle and upper bands. Minimum S₁₁ of -55 dB, -25 dB and -27 dB are obtained over the lower, middle, and upper bands respectively. The measured results validate the simulation ones.

This paper presents the ultraminiaturized implantable antenna based on a meander-line structure, specifically tailored for leadless pacemaker applications operating within the Wireless Medical Telemetry Services (WMTS) band of 1395-1400 MHz. The projected antenna has an ultraminiaturized volume of 3.25 mm³, surface area of 5 mm × 5 mm, and thickness of 0.13 mm. The substrate and superstrate were made of Rogers RO 3010 (ε_r = 10.2, tan⁡δ = 0.0035). Using a meandered line as the radiating element and including a shorting pin helps achieve impedance matching, reduces the overall antenna size, and improves the bandwidth performance. The proposed implantable antenna is validated using both homogeneous and heterogeneous heart phantoms. Experimental measurements were performed by embedding the antenna in minced pork tissue.; achieving a peak gain of -21.3 dBi and an impedance bandwidth of 360 MHz. Additionally, to ensure patient safety, Specific Absorption Rate (SAR) assessments were performed and the values are 202.52 W/kg (1-g) and 43.4 W/kg (10-g). With a 10 dB margin at 1.4 GHz, the results show that the antenna can successfully enable wireless communication at distances greater than 10 m.

This paper proposes a slot-loading-enabled compact ultra-wideband (UWB) planar antenna supported by circuit-backed modelling that targets defense communication systems. The antenna was realized on a compact footprint of 10 × 12 × 1.5 mm³, corresponding to an electrical size of approximately 0.29λ × 0.35λ × 0.043λ at the center frequency. Through the combined use of a modified circular radiator, strategically introduced slots, a stepped feed network, and a defected ground plane, the antenna achieves a continuous impedance bandwidth from 2.4 to 15 GHz. This corresponds to an absolute bandwidth of 12.6 GHz, a fractional bandwidth of nearly 145%, and a center frequency of 8.7 GHz, confirming the UWB operation. The antenna attains a maximum gain of 6.37 dB with a radiation efficiency reaching 89%. Stable radiation characteristics were observed, with dominant co-polarized fields and well-suppressed cross-polarization in both the principal planes. An electrical equivalent circuit provides physical insight into the multi-resonant behavior and enables efficient circuit-level validation. The measured results were in close agreement with the simulations, demonstrating the suitability of the antenna for compact UWB defense communication applications.

This paper focuses on enhancing the efficiency of wireless power transfer (WPT) using metamaterials (MTMs) only in the transmitter section, without modifying the receiver section. Power transfer efficiency (PTE) is the ratio of the actual power to the load resistance R_load that is transmitted to the load to the maximum available power at the source, V_s. Enhancing the PTE of a WPT system is essential, given the wide range of WPT applications. Magnetic MTMs can significantly increase the PTE. This research proposes a structure for the transmitter coil (Tx) and the receiver coil (Rx), incorporating the MTM slab, in a WPT system to enhance efficiency. The MTM was fabricated on a thin FR-4 substrate and positioned in front of and behind the Tx coil. Full-wave simulations show a clear improvement in coupling after adding the MTM plate. The transmission coefficient S₂₁ is increased by 0.4 when the MTM is placed in front of the Tx coil. When the two plates of the MTM were inserted, the S₂₁ improved by 0.2 compared to a single slab due to dielectric losses. In all cases, the magnetic field became more distributed and focused on the receiver side after the addition of the MTMs. The power transfer efficiency reaches 53.3% with double-layer MTMs at 12 MHz and a distance of 35 mm. Finally, the results of the measurements and simulations showed acceptable agreement, indicating that the proposed method is effective in overcoming reduced efficiency issues. The proposed design is suitable for various electronic applications, such as multiple-device charging pads.

In this paper, a high-sensitive microwave patch sensor for detecting adulteration in olive oil is proposed. First, a broadband electromagnetic property of olive oil adulterated with corn oil is characterized by using a Cole-Cole function. Next, a microwave patch sensor is designed with a circular patch integrated with a meandered slot and a complementary split ring resonator (CSRR) in the ground plane. A prototype of the microwave patch sensor is fabricated to detect the adulterant in olive oil. Results indicate that the proposed microwave patch sensor can detect adulteration ratio of corn oil in the parent olive oil ranging from 0 to 100%. The sensitivity, resonance frequency shift, and quality factors are 6.16%, 41 MHz, and 173, respectively. The proposed microwave patch sensor maintains a simple structure and electrically small size (ka = 0.83), high sensitivity, low cost, and ability to fast detect adulterant for olive oil.

This paper presents the design, simulation, fabrication and experimental validation of a compact millimeter-wave microstrip patch antenna intended for fifth-generation (5G) wireless applications. The proposed antenna employs a coplanar waveguide (CPW) feed, a defected ground structure (DGS), and truncated patch corners to enhance impedance bandwidth and radiation characteristics while maintaining a compact footprint. The antenna is designed on a Rogers RT/Duroid 5880 substrate (ε_r = 2.2, tanδ = 0.0009, thickness = 0.502 mm) and operates in the Ka-band with a center frequency of 30 GHz. Measured results demonstrate an impedance bandwidth from 29 to 34 GHz and a peak realized gain of 7 dBi, showing good agreement with simulated predictions. These results indicate that the proposed antenna is a suitable candidate for compact 5G millimeter-wave communication systems.

This letter presents a compact, low profile singe substrate transmissive linear-to-circular polarization (LCP) converter designed and experimentally validated for point-to-point THz communication bands. The proposed LCP converter consists of an H-shaped gold metallic pattern deposited on both sides of a 100 μm-thick fused silica substrate. The LCP converter operates within the 0.225-0.307 THz frequency band, achieving a simulated 3-dB axial ratio bandwidth of 30.8% in simulation. Owing to its wide axial ratio bandwidth, the proposed design is a promising candidate for point-to-point THz communication applications. The performance of the proposed converter is verified through surface current distribution, which explains the occurrence of Huygens response and equivalent circuit model. The proposed converter exhibits a measured 3-dB axial-ratio bandwidth of 27.8% in the frequency band 0.229-0.303 THz. The simple geometry and single-substrate implementation, with a thin profile and wide 3-dB axial ratio bandwidth, make the proposed design suitable for practical deployment scenarios.

Integrating Reconfigurable Intelligent Surfaces (RIS) with wideband systems, such as millimeter-wave (mm-wave) and terahertz (THz) systems, has shown great potential for improving communication system performance. However, accurate circuit-level modeling for RIS unit cell remains to date a significant challenge. This is because the unit cell in wideband systems faces a strongly coupled electromagnetic behavior that cannot be accurately captured using conventional circuit models. To address this challenge, this study introduces a novel hybrid modeling framework that combines Artificial Neural Networks (ANN) with discrete transfer functions H(z) for accurately modeling the unit cell in wideband systems. Specifically, the proposed framework allows a direct prediction of the H(z) coefficients from the S₁₂ data obtained from a full-wave Computer Simulation Technology (CST) simulation. The proposed framework aims to bridge the electromagnetic theory and circuit theory, which are considered to be complex, by representing the unit cell behavior using computationally efficient H(z) modeling. The results show that the proposed framework can accurately capture the sharp resonant characteristics of the RIS unit cell. The proposed hybrid framework achieves a performance improvement of 6 dB in Root Mean Square Error (RMSE) in comparison with the basic fitting model over all the Ka-band frequencies (30-40 GHz).

Vivaldi antennas loaded with metamaterials are currently being utilized in the form of reconfigurable metamaterial-loaded Vivaldi antennas, representing a promising class of antennas in advanced biomedical imaging and sensing applications. The design is an enhancement of the naturally ultra-wideband and high-directivity Vivaldi structure with the miniaturization and field enhancement properties of metamaterial inclusions. Frequency, polarization, and radiation pattern are some of the key features of biomedical diagnostics that can be dynamically reconfigured using tuneable elements like P-I-N diode, varactors, and graphene-based switches. This paper will give a summary of recent findings related to the design, analysis, and uses of reconfigurable metamaterial-loaded Vivaldi antennas in the field of biomedical imaging, especially in the determination of tumours and tissue characterization in non-invasive systems. The discussion notes the development of metamaterial integration methods, reconfigurable mechanisms, choice of substrate materials and their influence on the measure of antenna performance like gain, bandwidth and Specific Absorption rate (SAR). Moreover, fabrication strategies, experimental validation of the use of tissue phantoms, and performance comparison with the traditional antennas are tackled. The future research outlooks have been given at the end of the paper, highlighting compact and low-SAR and optically-controlled antenna architectures of the next-generation biomedical imaging systems.