Multi-resonator gap-coupled design of coaxially fed half-hexagonal microstrip antennas is proposed in 900 MHz frequency range. It yields an impedance bandwidth of 32 MHz (3.28 %) on a thinner FR4 substrate (~0.01λ_g). Reduction in patch area in the gap-coupled design is achieved by employing the ground plane slots. Slots reduce the fundamental mode resonance frequency on each patch, thereby realizing wideband response in a lower frequency region. With impedance bandwidth of 26 MHz (3.4%), slot cut ground plane design provides patch area reduction by 38.13% and frequency reduction by 21.8%. Enhancement in the broadside gain on a thinner lossy substrate in the gap-coupled designs is achieved by integrating a cavity-back structure, which provides gain increment by nearly 2.5-3 dBi. Thus, the proposed work outlines a technique that enhances the bandwidth and reduces the patch size with an increment in the gain, on a thinner lossy substrate. An experimental verification for the obtained results is carried out that shows a close agreement.

In this paper, a mode control technology of a slotline resonator is proposed and utilized to guide the design of the slotline resonator. With this method, characteristic modes generated by the slotline resonator are more controllable. With characteristic mode analysis, which is the core of this technology, the desired and unwanted modes of the slotline resonator are easy to be analyzed, controlled, and further used to expand the stopband bandwidth. By applying this technology, a multi-mode slotline resonator with a T-shaped coupling structure (MMSR-T) is proposed by modifying a multi-mode slotline resonator (MMSR), and its unwanted modes out of the passband are more controllable without influencing the expected modes in the passband. Based on the proposed MMSR-T, a balanced bandpass filter (BPF) is proposed, which consists of a U-shaped microstrip/slotline transition as the input/output structure, a T-shaped slotline feeding structure as a feeding terminal, and MMSR-T as the filtering unit. Through the mode analysis and design of MMSR-T, ultra-wide differential-mode (DM) stopband, high common-mode (CM) suppression, and high DM selectivity are obtained in this design. The measured results agree well with the theoretical predictions and simulated results. The effects of mode control technology on stopband extension are proven.

To solve the problem of antenna miniaturization and mutual interference between the communication band of the UWB system and other wireless communication system bands, this paper proposes a UWB monopole antenna which has frequency notch characteristics. By applying two pairs of Split Ring Resonator (SRR) structures on a CPW transmission line, a coupling resonance is generated in a specific frequency band, and the antenna has a dual frequency notch and a wide band notch function. The measured results show that the antenna has good band-notch characteristics in the frequency ranges of 3.3 GHz to 4 GHz and 5.1 GHz to 6.2 GHz, suppressing ultra-wideband interference between WiMAX (3.3 GHz~3.8 GHz) and WLAN (5.15 GHz~5.35 GHz and 5.725 GHz~5.825 GHz) in a wireless communication system. The volume of the antenna is 40 mm × 36 mm × 1 mm, and the measured results are compared with the simulated model results. Besides, the measured and simulated results have a good consistency.

A novel compact dual-band antenna based on dual-cap metasurface (MS) is proposed. By etching circumferential circular ring slots on one side of the substrate and large cruciform slot on the other side, the dual-cap MS operates in two frequency bands. In addition, by placing the dual-cap MS at the back of a circular ring planar antenna which serves as a reflector, the impedance characteristic of the antenna in lower band and gain both in two bands are improved. The results show that this dual-cap MS antenna operates in the Wireless Local Area Network (WLAN) bands of 2.43-2.6 GHz and 5.48-6.05 GHz. Moreover, the maximum gains in lower and upper bands can reach 6.9 and 5.8 dBi, respectively.

In order to achieve miniaturization and high performance in microwave filters, this paper proposes two double-layer bandpass filters with different structures, both equivalent to square-coupled topologies. These filters employ dual-cavity single-mode and single-cavity dual-mode substrate-integrated waveguide resonators. In this configuration, the upper layer comprises two single-mode resonators connected to the input and output feed lines, while the lower layer contains dual-mode resonators coupled to the upper layer's single-mode resonators through two slots on the middle metal layer. A comprehensive analysis is conducted on the impact of primary parameters on filter characteristics and transmission zero positions. The second filter is fabricated and tested, yielding results consistent with simulation outcomes. The center frequency of the filter is 4.77 GHz, with a 3 dB bandwidth of 0.16 GHz (relative bandwidth: 3.35%). Additionally, its rectangularity coefficient at 10 dB approximately equals one, an ideal value for practical applications.

The rapid expansion of wireless communication systems has spurred a growing demand for adaptable multiple-input multiple-output (MIMO) antennas capable of accommodating diverse frequency bands and operational environments. This paper presents a compact quad-port wide-band tuning-reconfigurable MIMO antenna tailored specifically for 5G applications operating within the sub-6 GHz spectrum. The proposed design enhances isolation levels (>18 dB) and augments pattern diversity by utilizing four orthogonal radiating elements. Integrating a C-shaped monopole element with a matching stub facilitates frequency tuning via a varactor diode, ensuring a consistent radiation pattern. The lower and upper resonant bands could be fine-tuned by adjusting the varactor diode's reverse-biased voltage within the allowed range of 0.5 to 10 V. These bands are 4 to 5.18 GHz and 5.45 to 6.65 GHz, respectively. The proposed antenna system's four C-shaped elements are placed on a 40 × 40 mm² ground plane and mounted on a Rogers RT5880 substrate that is 0.8 mm thick with a relative permittivity of 2.2. This design is well suited for various wireless applications and cognitive radio networks due to its compatibility with sub-6 GHz frequency bands and wide-band tuning capabilities.

A compact, spectacle shaped, tri-band, metamaterial inspired antenna is designed for ISM, WiMax, WLAN, Wi-Fi 6E 6 GHz, Aeronautical Radio navigation and Radio-Location Applications. The radiating electrical length is modified by two successive CSRR structures to mitigate the current and create a band notch at 3.9 GHz as well as 5.5 GHz. The proposed prototype is designed on low cost FR-4 material. Antenna performance parameters are investigated on a four-layered phantom model. The results obtained reveal that the antenna works well on free space as well as at the close proximity to human tissues.

Surrogate models have been gradually promoted in electromagnetic compatibility (EMC) simulation in recent years, and two typical application scenarios are uncertainty analysis and electromagnetic optimization design. The surrogate model can simulate the forward EMC simulation process as accurately as possible with relatively few sampling points. The choice and number of sampling points will directly determine the accuracy of the surrogate model. The purpose investigated by uncertainty analysis and electromagnetic optimization design is different. How to choose appropriate sampling strategies is worth discussing, but there are fewer studies in the field at this stage. This paper applies a cascaded cable crosstalk example to explore the accuracy of the surrogate model under different sampling strategies, which provides a theoretical level of guidance for the application of the surrogate model in EMC simulation. The study enables the surrogate model to be better suited for two application scenarios: uncertainty analysis and electromagnetic optimization design.

The proposed multi-resonant monopole antenna has a compact design and operates between 2.9 and 6 GHz, effectively covering the full 5G sub-6 GHz spectrum (N77/N78/N79) as well as WLAN frequency ranges. This Miniaturized Multi-resonance Monopole Planar Antenna (MMMPA), having dimensions 25 × 16 × 1.6 mm³ (L x W x h), is ideally suited for wireless communication devices and systems. The antenna achieves triple resonances, encompassing the frequency bands from 2.9 to 6 GHz, through an inventive construction consisting of rectangular patch, U slots, key-shaped slots, split ring resonators, and annular rings forming an electromagnetic band-gap (EBG) structure. A strong degree of agreement and correlation amongst the simulation and measurement findings attests to the antenna's dependable operation. Even though the patch size was reduced by around 65%.

The conventional synchronous generator model accurately represents only the stator circuit. However, when considering transient effects on rotor quantities such as rotor voltage and current, accurate predictions can be achieved by properly incorporating the field and damper considerations with the stator circuits in an equivalent model. Besides, it has been observed that simulated responses obtained using the conventional model with calculated machine parameters frequently do not align well with the actual measured responses, especially for the rotor winding. This paper analyzes the effect of the d and q axis parameters of synchronous machines, focusing on accurately determining these parameters, particularly the Canay inductance. It investigates the impact of precise determination of these parameters from the time constants of the direct axis operational inductance on transient response and stability. Through simulation studies on a high order model synchronous generator system, the paper compares transient performances with and without considering Canay inductance, shedding light on its effects.

We propose a 3-band iteration method to transfer knowledge learned from RGB (red, green and blue) data pretrained models to the hyperspectral domain. We demonstrate classification of a Multi-spectral Choledoch database for cholangiocarcinoma diagnosis. The results show quicker and more stable training progress: 92%+ top-1 accuracy in the initial 3 epochs. Some advanced training techniques in the RGB computer vision field can be easily utilized and transferred to the hyperspectral domain without adding more parameters to the original architecture. The computational cost and hardware requirements remain the same. After voting, the highest top-1 accuracy on the validation set reached 95.4%, and the highest top-1 accuracy on the test set reached 94.3%. We can directly use our models trained on high-dimensional spectral images to test and infer on RGB color images. We visualized some results by Grad-CAM (Gradient-weighted Class Activation Mapping) on RGB test data, and it shows the transferability of knowledge. We trained the models solely on classification task on spectral data, and these models showed their ability to predict on RGB images with different fields of views. The results indicate good segmentation even when the model has never been trained on any segmentation task.

In order to prolong the service life of lithium batteries, the charging process is usually divided into two stages: first constant current (CC) charging, and then constant voltage (CV) charging. This letter proposes a three-coil structure wireless power transfer (WPT) system to realize inherent CC and CV characteristics and automatic CC-CV transition function. During charging, the proposed system can operate in S-S-LCC tank for CC charging and in S-S-S tank for CV charging, respectively. Different from the previous closed-loop control, hybrid topology switching and dual-frequency switching methods, the proposed method has automatic CC-CV transition function due to the special circuit structure. Therefore, the communication links, state-of-charge detection circuits and open-circuit protection circuits are omitted, which ensures the high reliability and low cost of the system. Finally, a verification experimental prototype with a rated power of 480 W is built to verify the feasibility of the proposed system.

A compact four-port dual-band compact multiple-input multiple-output (MIMO) antenna system with reduced mutual coupling is proposed in this paper. The dual-band antenna operates in the frequency range covering 3.1-3.6 GHz (5G NR, n78) and in the newly introduced 5G midband spectrum of 5.925-7.125 GHz (5G NR, n96). The proposed MIMO antenna system is compact with dimensions 65 × 65 × 0.8 mm³ and has isolation ≤ -20 dB among all ports. The single monopole antenna is loaded with multiple resonant branches designed and optimized with impedance bandwidths of 14.92% at 3.35 GHz and 18.46% at 6.5 GHz. Impedance bandwidth, polarization diversity, and mutual coupling between elements for the designed four-port MIMO antenna system are measured. The proposed design is fabricated using an FR4 epoxy substrate, and the measured gain values are 3.9 dB and 4.8 dB for 3.3 GHz and 6.5 GHz, respectively, with nearly omnidirectional radiation pattern.

In the paper, a dual-band circularly polarized (CP) antenna with wide axial-ratio and gain beamwidths is proposed for high-precision BDS applications. The radiator is consisted of four groups of dipoles, eight metal columns, and a reflector. The half-power beam width (HPBW) can be effectively increased by bending a portion of the dipole into an arc and loading a series of metal columns on the ground. Besides, a reactive impedance structure (RIS) is inserted serves as a reflector to improve the axial ratio beamwidth (ARBW) and obtain unidirectional radiation. At the same layer of the dipoles, a four-feed network is presented to provide stable quadrature-phase excitation. For validation, the designed antenna is manufactured, where the overall size is 0.48λ₀ × 0.48λ₀ × 0.12λ₀. Measurement results suggest that the proposed antenna is capable of operating efficiently within the frequency range of 1.17-1.22 GHz (4.2%) and 1.5-1.65 GHz (9.5%), which covers BDS B1 and B2 band. Moreover, at four main planes, the measured 3-dB ARBW/HPBW are more than 121°/121° and 150°/198° at 1.207 GHz and 1.561 GHz, separately. Consider that the proposed CP antenna exhibits wide overlapped beamwidth and small size, it is conducive to high-precision positioning in BDS applications.

This paper introduces a 5G multi-frequency antenna design method based on multi-objective sequential domain patching. By etching helical metamaterials on radiation patches and loading asymmetric electric-inductive-capacitive metamaterials on the transmission line side, the antenna structure is designed and optimized using electromagnetic simulation software, HFSS, and MATLAB. The resulting multi-frequency antenna operates across multiple frequency bands: n1, n41, 3.5G, and 4.9G. To ensure antenna performance and radiation efficiency, the antenna multi-frequency bands are precisely controlled. The experimental results show that the error between each operating frequency band and target frequency bands of the antenna is within 7.2%. Compared with conventional antenna design methods, the use of metamaterials and intelligent algorithms to optimize the structural parameters and loading positions of metamaterials can improve antenna performance while shortening the design cycle. Overall, this research offers novel insights into the design of 5G high-performance antennas.

Orbital angular momentum (OAM) becomes a new resource for wireless communication due to the different modes being orthogonal. In OAM-based wireless communications, factors such as tilt and multipath distort the phase of the OAM beam, making the mode difficult to detect. We propose a multi-label class-specific lightweight neural network (MCSLNN) to measure tilt and detect mode from a single image. MCSLNN utilizes the MobileNetV2 network as the backbone feature extraction network, considering the terminal devices with limited computing resources. To improve the performance of multi-label classification, MCSLNN employs residual class-specific attention (CSRA) as the classification layer. Furthermore, MCSLNN employs the beam steering method to verify the correctness of the measured tilt. The network measures the tilt angle with an accuracy of 76% and an estimation error of ±1° in a validation experiment. Finally, we analyze the network's generalization from varying heights above the ground for reflection paths. The results indicate that MCSLNN is adaptable to diverse circumstances, thus making it suitable for 6G communication and radar applications.

Scattering of electromagnetic waves by a dielectric object can be described as an integral equation involving a Green function. These types of problems can be solved using a spatial spectral formulation, which requires sampling of the spectral Green function. To avoid sampling around the singularities on or near the real axis, the spectral Green function is represented on three separate complex paths. Using appropriate selection functions, these paths are recombined such that the original Fourier integrals are retrieved. This composite path method provides a general way to solve domain integral equations involving Green functions with simple singularities with minimal computational overhead.

An innovative ceramic filter is presented in this paper. The filter is composed of six tuning apertures, coupling channels, and a six-blind-hole coupling structure. The six blind holes are divided into two groups: one situated between the first and second cavities to induce inductive coupling, and the other positioned between the second and third cavities to facilitate capacitive coupling. Employing this structure facilitates the formation of a cascade quadruple (CQ) coupling unit among the 1, 2, 3, and 4 resonant cavities, thereby introducing two transmission zeros. Subsequently, an analysis of the influences of the depth and spacing of each blind hole on the coupling coefficients is presented. Finally, to further validate the theory, the filter tailored for base station applications was designed and implemented. The measurement results demonstrate a center frequency of 3.5 GHz with a bandwidth of 200 MHz. In the passband, the insertion loss was below 1.2 dB, and the return loss surpassed 19 dB. The test outcomes align closely with the simulation, confirming the reliability of the design.

A hybrid excitation variable-leakage-flux machine (HE-VLFM) for electric vehicles is presented in this paper, which places the field windings on the outer side of the stator and provides an axial magnetic field through the magnetic ring and the magnetic bridge. The HE-VLFM proposed in this paper has a rotor permanent magnet to provide the main magnetic field and an excitation winding to provide a variable auxiliary magnetic field, which can fulfill the requirements of the electric vehicle drive system with large torque at low-speed and wide speed regulation range. The electromagnetic performance of the proposed HE-VLFM is evaluated using the equivalent magnetic circuit method and three-dimensional finite element analysis and the results show that the HE-VLFM has a well-developed regulating flux capability.

We apply the third-order susceptibility tensor generated by the Simplified Bond Hyperpolarizability Model (SBHM) to address the long standing challenges in distinguishing the bulk and surface quadrupolar second-harmonic-generation (SHG) contributions in diamond lattices, such as silicon, which exhibit bulk inversion symmetry. Assuming that the quadrupolar contribution originates from the interface gradient of the excited electric field, we demonstrate through symmetry considerations and numerical calculations for Si(001) and Si(111) facet orientations that it is not possible to separate the different quadrupolar contributions when the incoming light is incident normally. However, we show that such separation is achievable with oblique incidence. Furthermore, we propose a novel experimental design to measure the bulk and surface quadrupolar SHG contributions separately by introducing a semi-vicinal surface. Using numerical SBHM simulations, we show for the first time that this semi-vicinal setup can prove the existence of spatial dispersion, a nonlinear dipolar bulk effect recently proposed. This approach may lead to a better understanding of various nonlinear contributions in silicon and enable precise nonlinear surface monitoring.