By using the time-dependent three-dimensional coupled-wave theory (3D-CWT), the transient analysis of photonic-crystal surface-emitting lasers (PCSELs) with double-lattice photonic crystals is performed. By optimizing the size of the PCSELs and the shape of the double-lattice photonic crystals, the resonance frequency is increased, and the damping (photon lifetime) is decreased, which enables over 40 GHz intrinsic 3 dB modulation bandwidth of the PCSELs. 100 Gb/s open eye under non-return-to-zero (NRZ) modulation is demonstrated by using such PCSELs. The large bandwidth enables single-lane 200 G optical transmission under four-level pulse-amplitude modulation (PAM-4). This study shows the design principles of large-bandwidth PCSELs and promises PCSELs to be an ideal candidate for the application of high-speed, high-power, free-space optical communication.

In this paper, a reconstruction methodology for the field emitted by an electronic equipment in a CISPR 25 standard environment is developed. It is based on an inverse method to determine equivalent dipoles representative of the electromagnetic sources. Positions and dipolar moments of equivalent dipoles are obtained via a hybrid optimization method, using a Genetic Algorithm (GA) followed by a Pattern Search (PS) method. First, the validity of the approach is verified with a numerical 3D model of a microstrip line. Then, an experimental protocol, corresponding to the setup of the CISPR 25 standard, is proposed and validated with a monopole antenna as a radiating source. As expected, the measurements obtained with the rod antenna yield some numerical errors related to the equivalent dipoles. However, such a compact model predicts the radiated field with sufficient accuracy to be useful for analyzing several EMC constraints in an automotive context.

A reconfigurable reflectarray antenna (RRA) is proposed with beam steering capability at 1.1 THz. The element of reflectarray is composed of vanadium dioxide (VO-2) and a gold bilayer model designed on a unit cell of 0.45λ, in which temperature variations produce different reflection phases due to the dependence of VO-2 on ambient conditions. The proposed reflectarray antenna has an aperture of 3100 μm and when particular cells of the array are exposed to temperature over 340K, it causes the phase in those unit cells to alter, eventually acting as 1-bit RRA. The radiation pattern shows a maximum gain of 24.3 dBi and a sidelobe level of -14.4 dB with an aperture efficiency of 21.7%. The maximum gain in case of offset is over 21 dBi with side lobe levels less than -10 dB up to 80-degree beam steering range. The proposed reconfigurable reflectarray antenna shows a beam steering capability of up to 100 degrees, which is sufficient for indoor communications. The designed antenna with its performance is optimum for the development of 6G RIS-based communication systems.

In this paper, we propose some suggestions for unsolved problems in classical and quantum electromagnetics. We aim to explain these problems in the simplest way possible. Some issues like the quantum computer may need a lot more work. The subject matter is interdisciplinary needing international collaboration in many different areas such as physics, math, engineering, and material science.

The Chu circuit model provides the basis for analyzing the minimum radiation quality factor, Q, of a given spherical mode. However, examples of electrically large spherical radiators readily demonstrate that this Q limit has limitations in predicting bandwidth. Spherical mode radiation is reexamined, and an equivalent 1D transmission line model is derived that exactly models the fields. This model leads to a precise cutoff frequency of the spherical waveguide, which provides a clear boundary between propagating and evanescent fields. A new delineation of `stored' and `radiated' electromagnetic energy is postulated, which leads to a new definition of spherical mode Q. Next, attention is turned to the Harrington bound on the directivity-bandwidth tradeoff of an antenna with an arbitrary size. Harrington derived the maximum directivity for a specified number of spherical harmonics such that the Q is not `large'. Here, the method of Lagrange multipliers is used to quantify the maximum directivity for a given bandwidth. It is shown that optimally exciting all spherical harmonics (including n>ka) enables both larger directivity and bandwidth than Harrington's previous limit. While Chu and Harrington's analyses are generally good approximations for most situations, the new self-consistent theory that defines fundamental antenna limits leads to updated results.

Reinforced concrete plays a vital role in the construction industry. Therefore, it is necessary to evaluate the parameters such as the number, diameter and protective layer thickness of rebar in concrete during and after the construction process. In this paper, we take the pulsed eddy current detection method as the principle, build the relevant experimental system, collect the data samples about the parameter information of the rebar, and propose an intelligent algorithm based on Convolutional Neural Network with Long Short-Term Memory (CNN-LSTM) based on Convolutional Block Attention Module (CBAM), which is capable of automatically extracting the relevant features of information-rich PECT signals, and the CBAM is introduced into CNN to enhance its feature extraction capability, which improves the accuracy and interpretability of CBAM-CNN-LSTM in predicting rebar information. In order to verify the performance of the method, traditional CNN, LSTM, and CNN-LSTM algorithms were used for comparison, and the prediction results were evaluated by decision coefficient (R²), Explained Variance Score (EVS), Root Mean Square (RMSE), and Mean Absolute Error (MAE). The experimental results show that the method is able to accurately predict the specimen information with good prediction accuracy and stability as the average error of the prediction of the number is reduced by 50% and the average error of diameter and thickness prediction reduced by 20% and 3% after adding the CBAM.

A novel metamaterial-element based frequency selective surface (FSS) is proposed in this paper for multiband radome for airborne application, which exhibits angular stability and polarization independence up to incidence angle, 60˚. The proposed metasurface radome consists of a combination of different patch-type elements in two cascaded layers, forming an electrically thin design suitable for aerospace applications. It operates in the frequency bands, S- (3.3 GHz), C- (4.8 GHz) and X- (9.1 GHz) with high transmission efficiency and good isolation between bands (< -20 dB). An equivalent circuit model of the proposed design is derived and validated with the simulated (based on HFSS) and measured results. Further, a multilayered radome wall configuration is designed using proposed metamaterial-element based FSS that exhibits transmission bandwidths, 220 MHz, 1 GHz, and 1.3 GHz corresponding to S-, C-, and X-bands, respectively w.r.t. -1 dB insertion loss. The structural analysis of multilayered radome wall configuration confirms its suitability for shared aperture antenna integrated to leading wing structure of aircraft.

To enhance the transmission rate and bandwidth utilization of Multiple-Input Multiple-Output (MIMO) communication systems, a dual-band MIMO antenna for millimeter waves is proposed, which is based on a substrate-integrated waveguide (SIW) and fed by a 50 Ω microstrip line. To achieve the dual-band performance, it employs a modified dual P-shaped slot instead of the conventional single P-shaped slot. The modified slot antenna generates dual-frequency radiation by exciting the primary and mixed modes in the circular resonant cavity. To improve the channel capacity of the system, the antenna is formed into a 2-element antenna, and the isolation of the antenna is improved by pattern diversity and defected ground structure (DGS). The antenna's dimension is 20 x 18.9 x 0.508 mm³. Measured results show that the impedance bandwidth of the antenna is about 26.7 GHz-27.9 GHz and 37.95 GHz-40.92 GHz with peak gain of 5.63 dBi and 6.35 dBi, respectively. In addition, the isolation degree is greater than 30 dB, the envelope correlation coefficient (ECC) less than 0.0002, and the diversity gain (DG) greater than 9.995. The antenna shows the advantages of low profile, dual-frequency radiation, and high isolation characteristics, which are well suited for millimeter-wave wireless communication systems.

With the increasing use of radar technology across various fields, electromagnetic pollution has become a growing concern, posing significant risks to human health. Consequently, there is a rising interest in developing wearable, flexible fabric-based absorbers that can efficiently absorb electromagnetic waves. However, the low dielectric constant of fabrics makes it challenging to achieve high absorption rates and broad bandwidth at low frequencies. To address this issue, in this study, we introduce a fabric-based broadband metamaterial absorber using felt as the dielectric substrate. The absorber features a centrosymmetric square block array design, incorporating a PU conductive film as the surface resonant material. By fine-tuning the parameters of each component in the absorber's equivalent circuit and optimizing structural parameters, the absorber achieves an extended bandwidth from 3.92 to 15.25 GHz, with a relative absorption bandwidth of 118.21%. Impressively, in the lower frequency C-band, the absorber maintains an efficiency of over 95%. The absorber was fabricated using the ``cut-transfer-paste patterning method.'' Testing results demonstrate that it is insensitive to incident angle and polarization and retains excellent absorption performance even when being bent.

This article proposes an 8-port MIMO antenna based on double-negative metamaterial Split Ring Resonators (SRRs) for three-dimensional (3D) non-planar applications, such as hotspots. The antenna features eight radiators arranged orthogonally to each other, placed in two perpendicular planes, operating at 3.5 GHz. Each resonator incorporates six embedded SRRs to enhance the metamaterial behavior, achieving a 40% size reduction compared to a conventional disc monopole at the same frequency. Simulated and measured results demonstrate excellent performance for MIMO applications, with Envelope Correlation Coefficient (ECC) values below 0.001 and Diversity Gain (DG) around 20 dB. The Total Active Reflection Coefficient (TARC) bandwidth is approximately 930 MHz at the -10 dB threshold. The S-parameters indicate excellent electromagnetic isolation between radiators exceeding 20 dB, and a very low cross-polarization level below -30 dB. However, the main limitation of this design is a reduction in gain, an expected result.

The time-varying amplitude error and phase error in the multi-channel will affect the system performance of Range Digital Beam Forming-Synthetic Aperture Radar (RDBF-SAR), which will lead to the elevation of the side lobes amplitude of the echo signal, thus affecting the quality of space-borne synthetic aperture radar (SAR) images. A multi-channel error compensation method for space-borne RDBF-SAR is proposed in this paper. The echo signals of each channel are aligned in the frequency domain. For the amplitude error, the amplitude error compensation factor is obtained by comparing the amplitude of each channel signal with the amplitude of the reference channel signal. For the phase error, the phase error compensation factor is obtained by conjugate multiplication of the phase of each channel signal and the phase of the reference channel signal. Reduce the amount of calculation by averaging. This method can well compensate the amplitude error and phase error, suppress the elevation of the echo side lobe, and make the synthetic aperture radar image more focused and accurate. Finally, the effectiveness of the method is verified by simulation experiments. Under the simulation conditions in this paper, the amplitude compensation reduces the side lobes pulse compression amplitude by 2~10 dB, and the phase compensation reduces it by -1~9 dB.

To enhance the performance of microwave power transmission (MPT) systems' transmitting arrays, it is essential to comprehensively consider key factors such as beam collection efficiency (BCE), the level of sidelobes outside the reception area (CSL), and expense. Current transmitting array models commonly suffer from issues like low BCE, a large number of array elements, and complex feeding systems. Addressing these issues, this paper proposes a novel transmitting array design referred to as Large Spacing Nonuniform-Excitation Sparse Planar Array (LSNSPA) and introduces a new subarray partitioning algorithm named Multi-Parameter Dynamic Weight Particle Swarm Optimization for Rectangular Subarrays (MP-DWPSO-RS). The algorithm is capable of optimizing the subarray structure, as well as the element positions and excitations, during each iteration. This paper achieves a relatively higher BCE metric than other arrays by utilizing only a small number of sub-arrays, through the combination of a large-spacing distribution strategy and a sub-array partitioning strategy. Simulations have verified that the proposed MP-DWPSO-RS algorithm can achieve a BCE of nearly 94% when optimizing the LSNSPA with an aperture of 4.5λ × 4.5λ consisting of 8 × 8 elements.

This paper presents a super-wideband antenna for operation in X, Ku, K, Ka, V, and W band applications. A monopole antenna with a semi-circular shape, fed through a transmission line and a Co-Planar Waveguide (CPW), is presented. It has a bandwidth ranging from 11.5 GHz to more than 100 GHz. A Multiple-Input Multiple-Output (MIMO) system with quad elements is constructed from the proposed antenna. The MIMO elements are arranged in an orthogonal ar-rangement to decrease the coupling between them. The MIMO system performance is investigated. The antenna is fabricated and measured, and it has a maximum gain of 8.37 dBi. The maximum radiation efficiency of the proposed antenna reaches 95% over most of the band. For the MIMO system, the maximum Envelope Correlation Coefficient (ECC) is 0.06, and the Diversity Gain (DG) is 9.7 dB.

To enhance the reduction of radar cross section (RCS) and improve stealth performance, a phase cancellation and absorbing metasurface(PCAM)is designed in this paper. The PCAM is composed of a chessboard layout of circular units and square units, and it not only converts absorbed incident electromagnetic waves into heat to reduce the intensity of reflected electromagnetic waves, but also simultaneously controls the phase of the reflected electromagnetic waves, achieving phase cancellation. This enables the metasurface to be exhibited with ultralow backscatter. After simulation verification, the metasurface can achieve RCS reduction of over 15 dB in the 4.3-11 GHz range for vertical incidence, with a fractional bandwidth of approximately 87.6%, and over 15 dB in the 5.4-11.2 GHz range for a 30° oblique incidence, demonstrating good stability for oblique angles. The metasurface has increased the reduction level from over 10 dB to over 15 dB, significantly enhancing the RCS reduction. Additionally, in the co-planar state with a central curvature of 90°, it can also achieve RCS reduction of over 10 dB in the 3.2-9.9 GHz range, showing significant potential for practical applications.

A compact antipodal Vivaldi antenna (AVA) integrated with circularly shaped loads and some elliptic slits etched in tapered slots is proposed in this paper. First, the elliptic slits etched in two tapered slots are employed for wideband application in X-band. Then, the value of max power capacity increasing from 0.47 MW to 0.82 MW is mainly due to two circularly shaped loads. Moreover, the size of the antenna is decreased to 0.44λ_middle × 0.42λ_middle. The configuration is measured to confirm the simulated results. Based on these, a novel antipodal Vivaldi antenna with compact size is successfully designed and applied in high-power field at X-band.

This study aims to improve the efficiency of constructing basis functions for solving the electromagnetic scattering problem of objects using the method of moments combined with compressive sensing and Krylov subspace. To this end, a region decomposition method based on a clustering algorithm is proposed to accelerate the construction process of Krylov subspace basis functions. First, the midpoints of the common edges of triangular pairs are used to form a clustered dataset. Then, the initial clustering center is set, and the processes of clustering center updating and regional decomposition of the constructed dataset are completed iteratively. Finally, each subdomain is expanded according to the average distance from data points to the clustering center to ensure the continuity of currents. The numerical computation results show that the proposed method can achieve significant time efficiency.

In recent years, uncertainty analysis has become a hot topic in the field of Electromagnetic Compatibility (EMC), and non-intrusive uncertainty analysis methods have been widely applied due to their advantage of obtaining results without modifying the original solver. Among them, the Surrogate Model Method has attracted widespread attention from researchers in the field of EMC due to its high computational efficiency and resistance to the curse of dimensionality. However, the issue of determining the convergence of the surrogate models seriously affects the computational efficiency and convenience of this method in practical applications. To address this issue, a convergence determination method for uncertainty analysis surrogate models based on Mean Equivalent Area Method (MEAM) is proposed in this paper. The complete convergence time of the Surrogate Model Method can be accurately determined through iterative calculation by this method, and the effectiveness of the proposed method is verified by calculating parallel cable crosstalk prediction examples from published literature. Finally, based on the proposed convergence determination method, the real-time convergence determination problem of the Surrogate Model Method is also preliminarily discussed in this paper, and by establishing a polynomial relationship, the real-time convergence of the Surrogate Model Method can be roughly determined.

Conventional sidelobe reduction methods such as analytical or parametric approaches and complex numerical optimization approaches were accomplished via specific tapering windows. Among all of the tapering windows, a rectangular window gives simplest array feeding network, narrower beam width, and highest directivity. The only drawback is its highest sidelobe level due to sharp edges at the array ends. In this paper, a simple trapezoid taper window, which is something between typical rectangular and triangular windows, is first suggested as a best compromise between uniform and non-uniform amplitude window functions. Then, it is further developed by making it adaptive or adjustable by including a number of controllable-amplitude elements in the linear edges of the trapezoid window. Thus, the proposed taper window becomes very flexible to accommodate different user-defined constraints. To find the optimal values of those controllable-amplitude elements, a genetic optimization algorithm is used to design and optimize the trapezoid window such that a desired sidelobe peaks and controlled nulls can be met while maximizing the complexity reduction as much as possible. The linear and planar antenna arrays are simulated to validate the superiority of the proposed taper window.

Inverse sliding spotlight synthetic aperture radar (SAR) is not as high as sliding spotlight SAR in azimuth resolution. Its azimuth resolution is constant, and it cannot meet the needs of multiple different azimuth resolutions. In order to solve this problem, a spaceborne inverse sliding spotlight SAR for nonuniform scanned scene is proposed. The design of the proposed inverse sliding spotlight SAR includes two parts: the design of the adaptive azimuth beam steering law and the design of the imaging algorithm. In the first part, the design of the adaptive azimuth beam steering law is based on multiple specific azimuth resolution requirements and the parameters of scanned scene. In the second part, the design of the imaging algorithm for the proposed inverse sliding spotlight SAR consists of three steps: filtering processing, phase compensation and upsampling processing, and image formation. Compared with the conventional inverse sliding spotlight SAR, the proposed inverse sliding spotlight SAR can achieve different azimuth resolution requirements for scanning targets at different positions in the scanned scene. Finally, the correctness of the proposed inverse sliding spotlight SAR is verified by simulation experiment and UAV SAR experiment.

Near-field scattering of human targets in the view of a bi-static, radar-like sensor operating in the lower radiofrequencies is used as an alternative to traditional biometric identification systems. These radiofrequency-based human sensor systems have emerged as a promising solution to address privacy concerns, particularly those associated with audio and visual data that extract sensitive personally identifiable information. In this paper, we propose a novel method for privacy-preserving human identification using bi-static radar-like sensors. Unlike conventional radar systems that rely on echoes and reflections in the far field, our approach is based on the transmission of signals through and around users as they pass through a transmitter and receiver. Instead of the more commonly used linear or segmented swept frequencies, this work utilizes discrete swept frequencies to transmit and receive radiofrequency signals. We have examined the performance of seven machine learning models in terms of accuracy and processing time and found that the Extra Trees ensemble model produced the best results, with an accuracy rate of 94.25\% for a sample size of 31 individuals using an Intel(R) Core(TM) i5-10300H CPU @ 2.50 GHz processor.