In this paper, a high-efficiency, center-fed dynamic seawater monopole antenna is proposed. The antenna's radiation efficiency increases by raising the feed point position, adding a metal tube above the feed point, and reducing the inner diameter of the water pipe below the feed point. Concurrently, the effects of the feeding position, the length of the metal pipe and the inner diameter of the water supply pipe on the current distribution are analyzed by theoretical modeling. FEKO electromagnetic simulation software is applied to simulate and analyze metal tubes with different lengths and water supply side pipes with different inner diameters. The simulation results indicate that the antenna attains optimal performance when being configured with a water supply pipe of 1 cm inner diameter and a 30 cm metal tube, achieving a maximum gain of 0.93 dBi and a peak radiation efficiency of 52%. Based on the simulation data, a simplified center-fed dynamic seawater antenna prototype is designed and fabricated. Experimental validation confirms that the seawater serves as the primary radiating element. The measured radiation characteristic curves exhibit consistent trends with the simulated results.

This article proposes a miniaturized dual notched ultrawide bandpass filter (BPF) for ultra-wideband (UWB) indoor applications. The initial operational spectrum recognition is realized through the resonances of multiple mode resonator (MMR). Then both the passband and stopband characteristics are improved substantially by mounting distinctly shaped meander resonators cascaded with open loop ring resonator on the MMR. Further, the interdigital coupled lines are also meandered to contribute in filter size reduction along with tightening the coupling between the effective filter structure and input/output ports. The elimination of interfering signals within the passband caused by C-band satellite downlink and fixed satellite service uplink is facilitated by two sharp notches at 3.76 GHz and 6.82 GHz frequencies. Concurrently, this miniaturized filter is also characterized by its wide passband of 6.42 GHz with fractional bandwidth (FBW) 110.88%, good selectivity of 0.85, minimal insertion loss differing between 0.44 dB and 0.85 dB, wide upper stopband of 5.11 GHz, etc. ensuring its suitability as a practical UWB filter. The design is fabricated and measured to compare with the simulated outcomes and validated by the obtained resemblance between the measured and simulated filter outputs.

A broadband efficient reflective linear polarization converter has been developed using a metasurface. The converter consists of a U-shaped array integrated with cross dipoles. The U-shaped unit facilitates cross-polarization conversion, while the cross dipole serves to broaden the operational bandwidth. It has been demonstrated that the proposed converter can transform an incident linearly polarized wave into its orthogonally polarized reflected wave across a broadband frequency range of 18.94-51.03 GHz with a conversion efficiency exceeding 90%. The efficiency remains above 90% even as the incident angle increases to 45°, within the frequency ranges of 19.18-20.19 GHz, 26.01-30.93 GHz, and 48.8-49.77 GHz. The strong electric and magnetic responses at multi-resonances reveal the broadband polarization conversion mechanism. A prototype was fabricated to verify the performance. Measured results exhibit good consistency with the simulated ones.

In this paper, a novel, compact, broadband circularly polarized (CP) semi-hexagonal monopole antenna is proposed. The antenna integrates a rectangular open loop and nonuniform asymmetric ground planes. The proposed design is fabricated on a 1.6 mm thick FR4 substrate with overall dimensions of 0.83λ_c × 0.70λ_c × 0.021λ_c at the center frequency f_c = 3.935 GHz. It achieves an impedance bandwidth of 4.51 GHz (1.68-6.19 GHz, 114.63%) and an axial ratio bandwidth of 2.6 GHz (2.3-4.9 GHz, 72.3%). The antenna offers realized gains of 1.4 dBi and 0.5 dBi, with corresponding efficiencies of 64% and 51% at 2.4 GHz and 3.5 GHz, respectively. It exhibits right-handed circular polarization (RHCP) across the ISM and WiMAX frequency bands. Furthermore, the antenna's performance is validated in a realistic environment using an Arduino-based wireless voltage monitoring system, demonstrating reliable data transmission with minimal loss. These results confirm the antenna's suitability for IoT applications requiring stable and efficient wireless communication.

A novel single-cavity triple-mode combined-type rectangular patch resonator (CRPR) is proposed in this paper, which is realized by integrating the rectangular patch structure with the rectangular substrate integrated waveguide (RSIW) structure. By cleverly designing the length-to-width ratios of both the RSIW structure and the patch structure, as well as the size ratio between them, the three higher-order modes of the CRPR can be resonance. Then, a highly selective bandpass filter (BPF) is realized through a special feeding structure. To demonstrate the method, an instance of a BPF is designed, synthesized, fabricated, and measured. The consistency of all results validates the effectiveness of the proposed design method. The proposed filter offers advantages such as relatively compact size, easy integration, and high selectivity.

This paper describes how the low sidelobe pattern synthesis of planar arrays with a distorted triangular or rectangular lattice, caused by row displacements, can be improved using the iterative Fourier transform (IFT) method. Array antennas with a rectangular, or triangular lattice combined with row displacements have an array factor that lacks periodicity in cosine u-v space for the u-direction. This means that for the u-direction, the pattern synthesis using the IFT method is limited to far-field directions that belong to the rectangular sector of the array factor computed by the inverse 2D FFT. Missing far-field directions in the pattern synthesis occur when the width of the computed array factor (AF) in u-v space is <2. In this case, not all far-field directions in visible u-v space are engaged in the pattern synthesis. The solution to this problem is to reduce the inter-element spacing along the rows with a factor two by including dummy elements with zero excitation between the active elements in each row. In this way, the width of AF, computed by the inverse 2D FFT, is doubled in u-v space. This doubling will result in twice as many far-field directions in the u-direction being involved in the pattern synthesis. After successful synthesis, all dummy excitations are removed from the synthesized set of excitations. The element excitations thus obtained, without the dummy ones, still perform the same as the original excitation obtained from the pattern synthesis. Three examples will demonstrate the validity of this solution.

This study investigates the relation between the physical parameters and the scattering parameter (S₁₁) curves of antennas, and proposes two deep-neural-network-based frameworks respectively for antenna forward and inverse designs, improving the design efficiency compared to the conventional electromagnetic (EM) simulation approaches. In this study, a one-dimensional (1D) U-Net is utilized as the backbone of the two models and is enhanced with multiple mechanisms - the diffusion mechanism, channel attention, and spatial attention. Therefore, the models more effectively capture the sequential features of data. In the forward design, the model quickly predicts the S₁₁ curves from given physical parameters with an accuracy improvement of at least 63% RMSE and 70% MAE compared to the improved one-dimensional convolutional neural network (1D-MCNN) and deep multi-layer perceptron (DMLP), thus realizing the surrogate model of conventional methods to some extent. In the inverse design, another model directly infers the physical parameters corresponding to the target S₁₁ curves with an accuracy improvement of at least 21% RMSE and 38% MAE compared to the baseline models (1D U-Net and MLP), thereby eliminating the iterative process of traditional methods and accelerating the antenna design. The experimental results demonstrate the significant advantages of the proposed deep neural network frameworks in terms of accuracy and efficiency for both forward and inverse designs of antennas, offering a powerful alternative to conventional electromagnetic simulation-based approaches.

This paper presents a varactor-tuned low-pass filter (LPF) with high sharpness-factor and steep stopband suppression at different tunable frequencies using defected ground structure (DGS). By periodic loading four series-parallel capacitive compensation DGS units with high quality factor Q and the varactor diodes in shunt, a central filter is formed. To suppress the spurious passband and improve the rejection of stopband, four extra units in the form of split-ring stepped-impedance DGSs also with high Q factor were introduced and loaded at both ends of the central filter. The prototype of the proposed LPF is designed, fabricated and measured. Simulation and measurement results exhibit a good agreement. The measured results demonstrate a continuous tuning range of 12-13.5 GHz for the cut-off frequency, with an insertion loss in the passband better than 0.8 dB and a sharpness factor less than 1.08 across the entire range. The stopband rejection level is better than 30 dB and can be extended up to 40 GHz.

Early detection of breast tumour is crucial for reducing the likelihood of mastectomy. To monitor the dielectric changes in breast tissue caused by the formation of tumorous cells, a novel biocompatible implantable antenna sensor is proposed. This flexible implant, measuring just 5 mm × 5 mm × 0.25 mm, operates in the ISM band at 2.45 GHz for real-time breast tumour detection. It is wirelessly powered via Wireless Power Transfer (WPT) operating in the mid-band range of 1.2-1.4 GHz. The antenna achieves an ultra-compact volume of 12.5 mm³ through closed-loop structures and meandered strips that enhance radiation efficiency. Inside abnormal breast tissue with a relative permittivity (ε_r) of 52.7, the antenna demonstrates a reflection coefficient of -17 dB and offers a -10 dB bandwidth of 330 MHz. The sensor is activated when the tissue permittivity rises above 15, achieving a maximum gain of -10 dBi. The antenna has been fabricated, and the simulated results have been validated in-vivo. This design enables proactive detection of tumour cell formation within breast tissue, allowing treatment before it spreads. It is particularly suitable for individuals with a genetic predisposition to breast tumour, offering continuous monitoring for early intervention.

Reconfigurable Intelligent Surface (RIS), as one of the potential key technologies for 6G, can effectively solve the problem of millimeter-wave links being obstructed by constructing an intelligent and controllable wireless communication environment. In this paper, a joint beam tracking algorithm based on RIS selection is proposed for the scenario of multi-RIS-assisted millimeter-wave vehicle-to-infrastructure (V2I) communication. The aim is to select as few RISs as possible to aid communication while the performance of beam tracking can be maximized. Firstly, the beam tracking model jointly composed of line-of-sight paths and virtual line-of-sight paths constructed by multiple RISs is derived based on the multiple-input-multiple-output model in a 3D road scene, and the beam tracking under this combined path is realized based on the Extended Kalman Filter (EKF) algorithm. Second, for the RIS-assisted millimeter-wave V2I scenario, a new metric to quantify the beam tracking performance is comprehensively designed based on the received signal-to-noise ratio, the beam angle variation, and the distance variation from the RIS to the vehicle. Finally, based on this metric, the joint beam tracking is realized by the RIS selection strategy and the EKF algorithm under the combined path. Simulation results show that the joint beam tracking algorithm based on RIS selection proposed in this paper has lower beam tracking error than the traditional signal-to-noise ratio based beam tracking algorithm.

Traditional ways of measuring compaction of asphalt, which involve destructive coring, are labor-intensive, time-consuming, and cause permanent damage to the road. This paper presents a non-destructive alternative using a dual-ring resonator sensor (DRRS) integrated with a Vector Network Analyzer (VNA) to evaluate asphalt compaction. The sensor design takes advantage of the electric field that forms between the first and second rings. This field can penetrate the asphalt layer to a depth of up to 50 mm and responds to changes in compaction levels. By putting asphalt samples of different densities on the sensor and measuring scattering parameters (S-parameters), changes in the resonant frequency are shown. These shifts were correlated with asphalt's physical properties through empirical equations. The results showed that the resonant frequency and the reflection coefficient (S₁₁) were -25.5 dB and 1.38 GHz, respectively, at a 75% compaction level. The frequency changed to 1.17 GHz at 100% compaction, and S₁₁ was -17.6 dB. Increasing the compaction of asphalt makes the air gaps in the material smaller, which makes its permittivity higher. Calibration was performed to mitigate the influence of temperature on permittivity measurements, thereby improving compaction. Overall, this method provides a fast, precise, and non-destructive way to check the quality of asphalt, significantly enhancing road construction and maintenance processes.

Pseudo-direct-drive (PDD) machine is a new type of permanent magnet machine with high torque density and efficiency. PDD with consequent poles can reduce the influence of outer PM on electromagnetic torque, but it has the disadvantage of high eddy current loss which will limit the range of speed. By transferring PMs from high-speed rotor to low-speed rotor, the eddy current loss in PMs is reduced, and the high-speed rotor is more robust. In this paper, a flux-switching consequent pole PDD (CP-PDD) machine is built. After optimization through a multi-objective genetic algorithm, the superiority of the proposed machine to regular CP-PDD is demonstrated by comparing it through the finite element method. The output torque of the proposed machine is greatly affected by the direct drive torque. A prototype is built and tested to verify the proposed machine. Results show that the proposed machine is more suitable for high-speed operation due to the reduction of loss and robustness of the high-speed rotor. The working temperature of the proposed machine is analyzed, and there is almost no irreversible demagnetization.

Hybrid excitation starter generator (HESG) has an increased number of magnetic potential sources, leading to issues such as complex magnetic circuits, numerous structural parameters, and low space utilization. These factors cause traditional analysis methods to have long cycles and low accuracy. In this paper, a new type of salient pole electromagnetic and permanent magnet composite pole HESG is proposed, and an analysis method combining hierarchical optimization and Taguchi method to analyze the influence of different structural parameters of composite pole rotor on the HESG performance is proposed. Response surface method was used to simulate the stator groove with multiple objectives, analyze the electromagnetic characteristics of HESG, complete the performance optimization, prototype, and conduct experiments. The results show that the amplitude of the air gap magnetic density base of HESG is increased by 7.4%; the distortion rate is reduced by 10.6%; the output voltage is increased to 127.68 V; the output performance and magnetization ability are significantly improved; and the overall performance of the HESG is improved.

Magnetic forces play a significant role in modern engineering applications, from medical imaging, data storage to transportation and industrial machinery. Accurate and efficient computational methods for magnetic force are necessary for engineering design and optimisation. However, different methods are typically based on distinct assumptions and are suited to different application scenarios. To assist researchers and engineers in selecting the most appropriate method for their specific needs, this review provides a comprehensive overview of various numerical approaches for calculating magnetic forces across different magnetic systems. Several key methods such as The Dipole Method, Filament Method, Finite Element Method (FEM), Energy Method, Maxwell Tensor Method, Integral Method and Boundary Element Method (BEM) are discussed in detail, demonstrating their fundamental theories, applicable scenarios, advantages, and limitations. Recent advancements and improved versions of these methods are also covered, demonstrating their enhanced accuracy and efficiency. In addition, the potential solutions of these methods and future directions of developing advanced magnetic force computation techniques are also discussed in this paper.

In this paper, a 4-port multiple input multiple output (MIMO) antenna with dual-notched bands and high interference rejection features is presented for ultra-wideband and beyond. The total volume of the intended antenna, computed at 2.63 GHz, is 0.52λ × 0.52λ × 0.014λ. The basic radiating element consists of a spatula-shaped patch etched with a U and an inverted U-shaped slots printed on the top of a dielectric substrate, which is backed by defected partial ground plane. With the goal of achieving good polarization diversity and high isolation, four identical basic elements are arranged in orthogonal way to form the MIMO configuration. The inter-element isolation has been improved by a swastik-shaped decoupling structure with its arms extended in the form of meander-lines. As a result, the isolation between diagonal and orthogonal elements is better than 20 dB and 25 dB, respectively with envelope correlation coefficient < 0.012 and diversity gain > 9.94 dB. The suggested antenna attains an impedance bandwidth of 2.63-18.44 GHz with ability to shield interferences from 3.38-3.90 GHz and 4.65-6.45 GHz, specifically targeting frequencies associated with WLAN/ISM and Wi-MAX/LTE bands, respectively. Moreover, it exhibits maximum radiation efficiency and gain of 97.88% and 5.94 dBi, respectively in the working band.

To achieve compact size and high electromagnetic shielding performance in RF systems, a substrate integrated half-coaxial line (SIHCL) structure is proposed. A new approximate synthesis method for the SIHCL is proposed using the equivalent capacitor. Subsequently, two fifth-order Chebyshev low-pass filters (LPFs) with a 0.1 dB ripple factor were designed and fabricated: the first implemented in the SIHCL structure and the second in microstrip technology. A comparison of the measured S-parameters between these two low-pass filters demonstrates that both near-end and far-end crosstalk is suppressed for the proposed SIHCL LPF, which is significant for high-speed and high-density integrated systems.

This paper presents a class of wideband hybrid couplers with enhanced isolation, based on an N-section phase shift filter network integrated into an unequal-split, multi-section branch-line hybrid architecture. The key innovation lies in the incorporation of the N-section phase shift network, which significantly enhances the fractional bandwidth with each increase in section and isolation performance compared to conventional designs. A detailed design methodology applicable for any N is developed and validated through the fabrication and testing of two microstrip prototypes for N = 3 and N = 4 at a center frequency of 1 GHz. Both simulated and measured results confirm consistent tight coupling, insertion loss better than 6 dB, and isolation exceeding 15 dB across all prototypes. Furthermore, N = 3 and N = 4 hybrids shows peak isolation of 87.4 dB, 96.8 dB in simulation and 66.5 dB, 72.7 dB in measurement respectively, at the center frequency of 1 GHz. Notably, the designs demonstrate a progressive improvement in the fractional bandwidth, achieving 73.68% and 91.89% for N = 3 and N = 4, respectively. This scalable and frequency-flexible design approach makes the proposed class of hybrid couplers highly suitable for modern microwave systems such as vector network analyzer (VNA) test set, applications in radar, communication receivers, and phased array antennas.

The low-noise amplifier(LNA) is the most vulnerable device in the front-door coupling path of the wireless communication link. When the electromagnetic pulse(EMP) is injected into the LNA circuit, it first generates the electromagnetic response with peripheral components, and then is transmitted further. This affects the pulse value transmitted to the internal semiconductor device and its degree of damage. The pseudomorphic high electron mobility transistor(pHEMT) type transistors are widely used in modern RF circuits because of their good stability and wide frequency characteristics. However, the frequency-selective characteristics of the front-end system exacerbate the electromagnetic coupling damage of the LNA circuit in some frequency bands. Therefore, in this paper, the vulnerable frequency points of the pHEMT LNA circuit under repetitive pulses are analyzed by injection experiment. It is found that both in-band and out-of-band lead to permanent damage to the LNA. For the more vulnerable 3 GHz frequency point, the electromagnetic response under injection withstand and absorption conditions was measured, determining that the gate external resistance offset follows a power-law relationship with the input power. Furthermore, the energy threshold was obtained, which assesses the energy that, after electromagnetic loss by an external 100 Ω resistor, is transmitted to the gate input and causes permanent damage to the LNA transistor. The breakdown damage mechanism of the gate-source of the LNA transistor is verified by failure analysis.

In order to meet antenna requirements for vehicular communication, a compact multiport MIMO antenna design is proposed for the n261 frequency band in 5G millimeter-wave communication. The 3D size of the antenna is 16 × 16 × 17 mm³. By optimizing the radiation patches and layout, a four-port MIMO antenna is developed, with adjacent antenna elements positioned on both sides of the dielectric substrate to minimize coupling between antenna units. Additionally, optimization is performed to achieve 360° radiation coverage for the multiport MIMO antenna. The simulation and measurement results show that the proposed antenna covers the n261 frequency band with an operational bandwidth. The overall isolation between ports of the multiport MIMO antenna is also relatively high. The 12-port MIMO antenna operates in the frequency range of 27.08 to 28.70 GHz, with a gain of 6.25 dBi, and its radiation pattern demonstrates diversity, providing complete 360 ° coverage in both elevation and azimuth planes. Therefore, the proposed antenna not only has a compact size and simple structure but also supports radiation propagation across multiple planes, reducing multipath propagation losses and enhancing communication quality and reliability. It satisfies the requirements of vehicular communication for 5G millimeter wave MIMO antennas.

In this paper the design of a cavity-backed slot antenna array with wideband operation and low sidelobe levels is introduced. A High gain metallic antenna array is designed using rectangular waveguides in both the feeding network and cavity-back slots, where a 16×16 array antenna is built with 8×8 subarrays. The antenna is fabricated using direct laser sintering (DLS) and computer numerical control (CNC) milling technology on both sides of each layer to guarantee no field leakage between antenna layers. For the sake of achieving a wide bandwidth in such array, a 1-to-64-way corporate feeding network is used to distribute the power in the lower feeding layer to excite the coupling apertures beneath the subarrays. The excited power coefficients through the array aperture are tapered using quasi-Taylor synthesis, with an even phase so the modified uneven power waveguide-splitter is designed to taper the field amplitudes within the feeding network till reaching the radiating slots. The array achieved a 14% bandwidth, a gain of more than 31.25 dBi over 1.85 GHz, sidelobe levels higher than 23 dB, and cross-polarization levels better than -40 dB, according to measured data.