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.

Microwave wireless power transfer (MWPT) offers significant advantages for charging unmanned vehicles over distances on the order of 100 m in atmospheric environments. To accurately measure the beam efficiency in field experiments, it is critical to suppress the impact of ground reflection on the field distribution generated by the beam. This paper presents the design of a compact wave-absorbing plate. The plate is composed of two dielectric waveguides arranged in an alternating side-by-side configuration. One waveguide is periodically loaded with metal patches along the propagation direction to absorb horizontally polarized incident waves, while the other is designed to absorb vertically polarized waves. Slots on the top surface are employed to couple the incident wave energy into the waveguides. Simulation results indicate that at 10 GHz, the reflection coefficients for both horizontal and vertical polarizations remain below -20 dB for incident angles ranging from 60° to 75°. In terms of volume, the proposed absorber achieves an 85% reduction in absorbing material consumption compared with conventional structures. It can be obliquely deployed on the ground as an array along the propagation path of the microwave beam to effectively attenuate ground reflection.

Millimeter-wave (mmWave) radio communication systems, essential to the advancement of future networks, are highly susceptible to link degradation caused by human body obstruction. This paper presents a comprehensive experimental study of fast fading phenomena induced by pedestrians crossing indoor mmWave links, specifically at 40 GHz and 60 GHz. The measurement campaign was conducted in a realistic access point to user equipment configuration, involving over 150 participants and yielding 604 fading events, of which 431 involved full line-of-sight (LOS) blockage. The analysis focuses on the statistical characterization of the deep-fade regions within these events. Results are compared with simulations based on the Knife-Edge Diffraction (KED) model to evaluate its accuracy under dynamic blockage conditions. The statistical analysis reveals that the Weibull distribution most effectively models the fast fading observed during human-induced blockage, outperforming Rician, Rayleigh, Nakagami-m, and Normal distributions - particularly at 60 GHz, where 89% of fades aligned with the Weibull model. Simulated fades using the KED model, however, did not show a strong fit with a single distribution yielding similar results to the Rician, Weibull, and Nakagami-m. These findings underscore the influence of diffracted multipath components in determining the statistical behavior of fast fading. The study confirms the limitations of existing diffraction models in capturing the full complexity of dynamic human blockage and highlights the need for refined modeling approaches. This work contributes critical insights toward the robust design and performance prediction of future indoor mmWave communication systems.

With the increase in users' demand, the wireless communication systems are expected to operate by considering microwave and millimeter wave signals under higher power intensity by means of multichannel propagation. Therefore, the nonlinear (NL) effect becomes a major challenge to maintain the communication system performance. To deal with such an undesirable effect, the microwave amplifier (MA) NL characterization requires a relevant modelling technique. The intermodulation distortion (IMD) constitutes one of the basic approaches for MA NL analyses. The IMD of the MA two-tone (TT) response in weakly NL behavior is modelled and measured in this paper. The modelling method is empirically derived from the Volterra series coefficients of the MA input-output characteristic from a single-tone (ST) test. The mth-order IM amplitudes of MA NL TT response are formulated as a function of the ST odd harmonics. The efficiency of the IM(m) models is experimentally validated with TT measurements of Gallium Nitride MAs around 2.4 GHz and 24 GHz carrier frequencies. The behavior of the IMD3 and IMD5 of weakly NL (WNL) models around 2.4 GHz is in good agreement with the TT input amplitude measured from -25 to -5 dBm. The IMD3 WNL model around 24 GHz is also well-correlated to measurement with input amplitude range from -20 to -3 dBm. In the future, the developed NL model can be exploited for assessing the MA impact on the microwave system communication performance.

A hybrid excitation linear machine with all excitations on the primary has the advantage of low cost in long-stroke applications and flexible flux regulation. The permanent magnet and field winding concurrently contribute to the effective thrust force, that is, the permanent magnet excitation thrust force and electrical excitation thrust force. However, the insufficient utilization of the two magnetic fields limits the thrust force enhancement. To enhance the thrust force, this study proposes a flux-modulated hybrid excitation linear machine with improved concurrent utilization of air-gap magnetic fields from permanent magnets and field windings. First, the topology and operating principle of the machine are interpreted. An analytical model was built to analyze the air-gap magnetic field harmonics and flux linkage from the permanent magnet and field winding. In addition, the electromagnetic performance, including the flux regulation capability and thrust force, was investigated using finite element analysis. It was found that its average thrust force and flux regulation capability were significantly improved compared with the counterpart.

This study presents the design, simulation, and fabrication of a compact patch antenna with metamaterials, dedicated to biomedical applications. The proposed antenna was implemented on an FR4 substrate and resonated at a center frequency of 2.48 GHz. By the integration of metamaterial (MTM) unit cells as the primary radiating element, the design achieves performance improvements compared with traditional patch antennas. The return loss was reduced from -13.45 to -67.20 dB, which indicates improved impedance matching. In addition, the antenna showed enhanced radiation characteristics, with a gain of 1.96 dB and a directivity of 3.10 dB. As the antenna was designed for biomedical use, specific absorption rate (SAR) analysis was conducted to ensure compliance with safety standards. A prototype of the antenna was fabricated to validate the simulation results, and the measured results matched the simulations, which confirms the reliability of the suggested design. The simulation results were obtained using HFSS and CST. Overall, the results demonstrate that the proposed metamaterials-based antenna is a strong candidate for integration into biomedical devices.

To meet the requirements of antenna miniaturization and wide impedance bandwidth in UWB systems, a novel compact UWB Vivaldi antenna is presented in this work. Based on the conventional planar Vivaldi configuration, the radiating arms are etched with elliptical slots, and the front end of the tapered slot is loaded with concentric arc parasitic patches to regulate the surface current distribution and enhance broadband impedance matching. Simulated and measured results demonstrate that the presented antenna achieves a reflection coefficient below -10 dB over the frequency range of 6.61-21.06 GHz, corresponding to a relative bandwidth of 104.45%, with a compact size of 14.5 × 19.8 × 0.51 mm³, while maintaining a single-layer planar structure without increasing structural complexity. It is also indicated that stable end-fire radiation characteristics and low cross-polarization levels are maintained at several representative frequencies. The presented design simultaneously realizes significant size reduction and ultra-wide impedance bandwidth, providing a simple and practical solution for compact UWB Vivaldi antenna applications.

To achieve the dynamic decoupling of a permanent magnet-assisted bearingless synchronous reluctance motor (PMa-BSynRM), this study proposes an innovative decoupling control strategy. In this method, the inverse system is constructed by improving a genetic algorithm optimized fuzzy neural network to achieve decoupling control. Firstly, this article elucidates the structure and working principle of PMa-BSynRM, establishes a mathematical model, and conducts reversibility analysis. Secondly, by optimizing the fuzzy neural network through improved genetic algorithm, a system inverse is derived to achieve the decoupling of the initial system, transforming it into a linear-like system. Thirdly, the decoupling performance of the proposed control method for a 5-degree-of-freedom (5-DOF) system is validated through simulation. Finally, experimental validation is conducted on both 2-DOF and 3-DOF subsystems. Simulation results for the 5-DOF system and subsystem experiments indicate that the proposed method exhibits excellent control accuracy, rapid convergence, and dynamic anti-interference performance.

A corner-truncated (linear and circular) antenna with a compressed reduced ground and parasitically loaded with a single unit of SRR was successfully designed, fabricated, tested, and investigated for 5G wireless communications. The truncated corner with a full ground shifted the narrow bandwidth and resonating frequency (5.10 GHz) from right to left (2.81 GHz). The ground-reduced length and compressed width enable a transition from a narrow band to a wide band, and the antenna is tuned to approximately 3.5 GHz. The antenna is parasitically loaded with an SRR that provides an additional resonating frequency within a wide bandwidth (2.82-5.21 GHz). The antenna achieves wideband with dual tuning frequencies within the band. The antenna has gains of 3.93 and 4.25 dBi at the tuned frequencies, respectively. The truncated ground enhances the antenna gain (3.33 to 4.25 dBi) and impedance bandwidth from narrow band (5.07-5.17 GHz) to wideband. The truncation of the corner and reduced ground length degrades the radiation efficiencies, while ground and substrate dimension (length and width) compression compensatea for the reduced values of efficiencies. The proposed antenna is best suited for Wi-Fi 5 (IEEE 802.11ac), Wi-Fi 6 (IEEE 802.11ax), n48, n77, n78, and n79 applications. The antenna was measured and compared with the simulated results and radiation patterns. They were found in approximations, which helped confirm the antenna design and investigations.

To reduce the implementation complexity of reconfigurable sparse arrays, this study proposes a low-complexity group-sparse orthogonal matching pursuit (G-OMP) algorithm with a minimum spacing constraint for synthesizing sparse arrays with multiple beam-shared element positions. An off-grid OMP algorithm with a minimum spacing constraint can mitigate the accuracy degradation caused by fixed-grid discretization, thereby ensuring the practical feasibility of engineering implementations. To enable beam reconfigurability, a group-sparse structure is incorporated into the off-grid OMP algorithm, and a multi-beam group-sparse reconstruction algorithm based on a dynamic grouping strategy is proposed, allowing multiple beams to share sparse array element positions. Simulation results show that, under the simulation parameters, the proposed algorithm achieves low computational complexity while maintaining good radiation pattern performance.

The relative value of the stored energy in the dielectric and that in the surroundings for a cylindrical dielectric resonator in a closed metal cavity was studied using a simple electromagnetic field theory model. The influence of this factor on the measurements of the loss tangents of dielectric samples with different dielectric properties and dimensions at their microwave resonant frequencies was discussed. In addition to the traditional calculation method, a perturbation method with a much simpler computation procedure was also adopted for the energy factor calculation, and its accuracy was compared with that of the traditional method.

A low-profile, dual-band, shared-aperture antenna with a large frequency ratio is presented, based on a meshed patch and an AMC-backed Fabry-Perot (F-P) cavity. By taking advantage of the weak frequency sensitivity of grid slotting in meshed patches, the upper meshed patch is utilized as both the parasitic patch for the low-frequency antenna and the partially reflective surface (PRS) for the high-frequency F-P cavity, thereby simplifying the overall structure. Meanwhile, the AMC ground is employed to control the reflection phase and reduce the cavity height to λ/4, which enables both antennas to share the same aperture within an 8-mm profile. A prototype is fabricated and tested at 1.6 GHz and 15.14-15.46 GHz. Measured results demonstrate a frequency ratio of 1:9.6, a peak gain of 6.2 dBi at 1.6 GHz, a peak gain of 11.8 dBi in the high-frequency band, and a port isolation better than 17 dB. The proposed antenna features compact size, low profile, and efficient structural reuse, making it attractive for integrated multi-band communication systems.

We present a review of homogenization models of microwave wire media with different geometries. We begin with a simple (uniaxial) wire medium and then consider more complex types of wire media - double, triple, and interlaced wire media - which remain underexplored. We discuss boundary problems with wire media and the most important physical effects revealed using the reviewed homogenization models.

This study presents a method for generating multiple electromagnetic field minima in specified spatial regions. The relationship between the complex amplitudes of signals at receiving points and those of radiated signals is described using an S-parameter matrix. It is shown that the determination of the complex amplitudes of the radiated signals can be reduced to solving an underdetermined system of linear algebraic equations, which may be unstable because such a system can admit either infinitely many solutions or no solution. To address this issue, an optimization problem is formulated based on minimizing the squared error between the required and obtained electric field distributions. Its solution leads to a new system of linear algebraic equations, to which Tikhonov regularization is applied to ensure the stability and uniqueness of the solution. The proposed approach is validated by mathematical modeling for three electric field configurations, with the complex amplitudes of the radiated signals determined for each configuration. The modeling results confirm the correctness of the theoretical conclusions.

This work presents deep neural networks for the inverse design of an ITO-film angular-selective metasurface absorber. A tandem deep neural network (T-DNN) framework is developed for the inverse design of electromagnetic metasurfaces. A forward network is first trained independently to learn the complex physical mapping between metasurface structures and their electromagnetic responses. An inverse network is then trained in tandem with the pre-trained forward network, eliminating conventional parameter-by-parameter tuning and establishing a performance-driven pipeline that directly maps target electromagnetic responses to structural parameters. Using the trained network, several metasurface absorbers with distinct angular sensitivities are rapidly designed, and their angle-dependent applications are preliminarily investigated. Results show that deep learning enables the fast design of metasurface absorbers customized to realistic incident angle distributions, yielding efficient omnidirectional radar cross-section (RCS) reduction at sensitive angles. This work offers a new strategy for the fast design of omnidirectional scattering suppression.