In this paper, a miniaturized coplanar waveguide (CPW) to rectangular waveguide (RGW) transition using integrated resonators and variable housing is proposed. By properly designing the dimensions of the integrated resonators and variable housing, a compact and broadband transition can be accomplished. The -15-dB fractional bandwidth of the transition is as broad as 45.2%, which ranges from 8.21 GHz to 13 GHz, covering the whole X-band (8.2-12.4 GHz). Besides, the transition size is as small as 3.94 mm. To reduce the mechanical complexity, the housing height is from 24.5 mm to 22.86 mm, which is equal to the height of the rectangular waveguide. The -15-dB fractional bandwidth of the transition is as broad as 45.5%, which ranges from 8.18 GHz to 13 GHz, encompassing the whole X-band. Besides, the transition size is still as small as 3.94 mm. To verify the simulations, a back-to-back CPW-to-RWG transition is fabricated and measured. The simulation and measurement results are in good agreement.

A novel filtering crossover featuring flexibly allocated center frequencies based on ridged substrate integrated waveguide (RSIW) is proposed. Two TE₁₀₁-mode SIW cavities, two loading single ridge SIW (SRSIW) cavities and a loading triple ridge SIW (TRSIW) cavity are used to realize the filtering crossover. Good transmission and isolation responses can be achieved based on orthogonal degenerate TE₁₀₂ and TE₂₀₁ modes in the centered TRSIW cavity. The frequency ratio of the TE₁₀₂ and TE₂₀₁ modes can be significantly improved by adjusting the aspect ratio and the dimensions of ridges in the centered TRSIW cavity. A prototype operating at 4.98 GHz/10.1 GHz is fabricated and measured. The measured results demonstrate excellent agreement with the simulated one.

Multiple-Input Multiple-Output (MIMO) antennas are essential for transmitting and receiving information in Vehicle to Everything (V2X) communication. However, the MIMO antenna designs at V2X are complex because of the mutual coupling problem. Several approaches have been designed to improve antenna isolation. However, these approaches have drawbacks like gain, bandwidth, and radiation efficiency reductions. This work introduces a compact four-port MIMO antenna that operates at a 5.85 GHz to 5.9 GHz frequency range for V2X communication. Here, the slotted circular microstrip patch MIMO antenna is considered. The antenna's length, width, and patch are optimized by metaheuristic optimization called Aquila Optimization (AO). A substrate Rogers RT5880, which has a defected ground structure (DGS) and a parasitic patch, is used to design the antenna. F-shaped parasitic elements are placed near each antenna element to improve isolation. The DGS with a U-shaped parasitic element minimizes the mutual coupling among the adjacent antenna elements. The considered overall dimension has a compact size, and it achieves better envelope correlation coefficient (ECC < 0.5), total active reflection coefficient (TARC < -10 dB), diversity gain (DG > 9.9 dB), channel capacity loss (CCL < 0.4), and mean effective gain (MEG < 3 dB) at 5.88 GHz. Hence, it is proposed that the developed design is useful for applying V2X communications.

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.

In this contribution, two antennas for microwave imaging are described and validated. The first solution is a slot antenna designed when it works a direct contact with human head. However, the air-gap issues and hair layer degrade the antenna performances. These limitations are overcome with the cylindrical brick antenna containing coupling liquid medium. Basically, this antenna consists of a ground plane hosting a wide slot and a microstrip feed line with a fork-like tuning stub inserted within the circular container. Numerical examples show that the proposed antenna exhibits S₁₁ below -10 dB over the selected frequency band from 1 to 2 GHz, in agreement with microwave brain imaging systems. Moreover, the antenna is assessed in terms of transmission coefficients and field penetration. In particular, it is shown that such a feature holds true when the antenna is placed in different positions over the head, when it is located on both the skin and the hair. Experiments on a few real humans confirm the numerical results. The transmission coefficient, which is the only one used in imaging systems to streamline the hardware complexity, is of comparable level of other similar antennas already present in literature. However, the proposed antenna is lighter and smaller in size.

A fully numerical process for the systematic design of fully-planar antennas for 5G communications frequencies is presented, utilizing a metamaterial-enhanced SIW as the basis platform. A combined modal analysis and wave propagation Finite Element modeling is proposed for the accurate design of the waveguiding structure towards its leakage loss minimization. Based on this robust numerical schemes, two different types of fully-planar antennas are designed. A leaky-wave fully-planar two-slot antenna and an H-plane end-fire sectoral horn antenna. Both structures are viable candidates for integration in 5G communications platforms, exhibiting attractive characteristics such as optimized gain and bandwidth, low cost, compactness, and ease of fabrication.

To address the problems that the traditional permanent magnet synchronous motor air-gap flux is difficult to adjust and that the weak magnetic speed expansion ability is poor, a new series-connected hybrid excitation permanent magnet synchronous motor is proposed. A DC excitation winding is added to the rotor, allowing the excitation field generated by this winding to form a series connection with the magnetic field of the permanent magnets. The structure of this paper includes an overview of the novel rotor structure and principle of operation. For the complex rotor structure, a multi-objective genetic algorithm is used for optimisation, followed by finite element analysis to compare the performance of the initial motor, the optimised motor and the conventional motor in terms of no-load air-gap magnetism, reverse electromotive force as well as output torque and efficiency. The magnetic load of the motor in the demagnetized state is increased from 0.2 to 0.266 compared to the unexcited state, and the magnetization capacity is improved by 33%. The output torque of the optimized motor is 252 N.m at low speed; the output torque of the conventional motor is 220 N.m; and the starting torque of the motor is improved by 14.5%. The maximum speed is increased from 10,000 rpm to 11,500 rpm, and the speed expansion capacity is improved by 15%. The effectiveness and feasibility of the series-connected hybrid excitation permanent magnet synchronous motor are verified.

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.

In this paper, a hybrid method is proposed for electromagnetic vibration prediction of flatted single-layer interior permanent magnet synchronous machines (IPMSMs) for flywheel application. The proposed hybrid model combines the mesh-based equivalent magnetic network (EMN) model and vibration transfer function method. A small size 4-pole/6-slot flatted single-layer IPMSM for demonstration purposes is manufactured to illustrate the proposed hybrid method. Firstly, the modeling method of the proposed mesh-based EMN model is introduced, and the electromagnetic forces are calculated. Second, the vibration transfer function construction method is introduced. Thirdly, the modal superposition method is applied to compute the electromagnetic vibration acceleration of the 4-pole/6-slot IPMSM. Finally, the simulation and experimental test at rated rotational speed condition are used to verify the effectiveness of the proposed hybrid method, and the vibration acceleration at twice the fundamental frequency from proposed method has the acceptable agreement with tested and simulation. The proposed method can be applied to predict the electromagnetic vibration for flatted single-layer IPMSM with concentrated winding at different operating conditions.

This paper presents a Time Reversal (TR) application to mitigate the grating lobes of an arbitrarily spaced array for a through-the-wall imaging radar (TWIR). Analytical modeling and simulation of array of arbitrarily located elements with (i) conventional and (ii) time reversal beamforming have been carried out. The results are analysed and compared. The array is used to image a target using the multipaths in a typical TWIR environment. The Time Reversal technique as spatial correlator improves the performance of the arbitrarily located array which is akin to the array thinning of conventional array processing. It is demonstrated that the TR beamforming can mitigate the grating lobes of large sparse array with a fewer elements. The performance metrics are captured in terms of Side Lobe Levels (SLLs) and image radius. The SLL performance and image radius are benchmarked for different configurations of array. It is shown that a fewer-element sparse array with Time Reversal is feasible for practical TWIRs.

This paper designs, simulates, fabricates, and measures a right hand circular polarization (RHCP) array antenna, which is based on a low temperature co-fired ceramic (LTCC) and quartz interposer. The proposed array antenna consists of $4\times 4$ antenna cells, and axis ratio of the antenna element in array antenna can be optimized after array expansion. This RHCP antenna's wide frequency band and good axial ratio band are obtained by the stacked patches. The thickness of the proposed antenna without fixed structure is about 1.7 mm, and it is realized by a LTCC substrate with 14 layers and a quartz interposer with the thickness of 0.254 mm. The measured results demonstrate that, for the operated frequency band of 17.5 GHz~21.5 GHz, the VSWR of the proposed antenna is better than 1.7, the RHCP gain more than 15.5 dB, the axial ratio less than 3 dB, and the size of the proposed antenna without connectors is 29.6 mm × 29.6 mm × 1.7 mm.

The conventional DITC strategy for switched reluctance motor relies on current for control, while the use of current sensors increases the complexity of the system, and the torque ripple in the two-phase exchange region of the conventional DITC strategy is too large. To solve the above problems, a current sensorless interval torque control (CSITC) method is proposed. Initially, the equivalence between torque and acceleration control is established, replacing the torque loop with an acceleration loop. This forms a dual closed-loop system with the speed control loop, enhancing system stability. Subsequently, the variation of the output torque capacity of phase winding of the motor in each conduction region is analyzed, and combined with the inductive characteristics of the motor windings, the two-phase exchange region is divided into two subregions. Different acceleration hysteresis loop control strategies are adopted for the phase windings in each region, so as to realize the stable output of the motor torque. Finally, a three-phase 6/20 permanent magnet assisted-switched reluctance motor (PMa-SRM) is used for simulation and physical verification. The results show that the method can still achieve the steady state of the motor when only the position sensor is used and effectively reduces the torque ripple in the exchange region.

Chipless RFID technology offers a cost-effective and durable alternative to chipped tags for identification and tracking applications. By eliminating the need for an integrated circuit, chipless tags are cheaper and can withstand harsher environments. This opens doors to not only track items throughout a supply chain or monitor valuable assets, but also integrate basic sensors for functionalities like environmental monitoring or smart agriculture. However, limitations in data capacity, read range, and decoding complexity currently hinder their full potential. This paper explores the application of machine learning techniques to improve the interrogation process and enhance the reliability of chipless Radio Frequency Identification systems. The effectiveness of machine learning in optimising chipless RFID systems hinges on the richness and variety of training data. A robust dataset encompassing diverse tag characteristics, environmental factors, and reader configurations is paramount. Nevertheless, gathering real-world RFID data can be difficult. To address this, a data collection procedure has been specifically designed to gather backscattered information from the chipless tags at multiple orientations and distances. Four binary combinations of a 5-bit RFID tag based on frequency-selective surfaces operating in the 2–8GHz range are considered for generating the database. The dataset is then used to train and validate various classification models, including support vector machine (SVM), k-nearest neighbour (k-NN), Decision Tree (DT), Naive Bayes classifier, and Logistic Regression (LR). The proposed Support Vector Machine model is able to identify the tag at a distance of up to 70 cm from the interrogator, with multiple rotational degrees of freedom.

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 single-layered monopole wideband combinational reconfigurable antenna for 4G and 5G applications is presented in this paper. Coplanar waveguide (CPW) feeding method is utilized to get single-layered structure. The three characteristics of this antenna are reconfigurable: frequency, polalization, and radiation pattern. This antenna consists of a parasitic element attached to a rectangular ring antenna. An RF-PIN diode is used to connect this parasitic element to the loop antenna. Additionally, two parasitic elements are connected to the ground plane of the proposed antenna via a pair of RF-PIN diodes. The suggested antenna functions in seven distinct states with the use of these three RF-PIN diodes. The suggested antenna operates at frequencies of 3.24-3.52 GHz, 2.78-2.94 GHz, and 2.54-2.9 GHz with an omnidirectional radiation pattern in states 1, 2, and 5. In states 3 and 4, it has an end-fire radiation pattern in the left and right directions of the proposed antenna, covering a wide frequency band of 2.47-3.57 GHz. Lastly, the suggested antenna operates in dual bands at frequencies of 2.49–2.9 GHz and 3.6-3.76 GHz in states 6 and 7. It offers reconfigurability of polarization at the higher band. The suggested antenna is made of glass epoxy FR-4. For verification of the suggested antenna, the prototype is designed and tested. The simulated and experimental results agree quite well.

The growth of 5G communications has created a demand for advanced wearable and flexible antennas due to supporting the high speeds, low latency, and capability of mechanical deformation conditions such as bending and conformability. In this paper, the design and analysis of a defected ground structure (DGS)-based ring slot antenna for N77 (3.3-4.2 GHz) and N78 (3.3-3.8 GHz) frequency bands is demonstrated. The antenna is made of an RT/Duroid 5880 substrate and has a loss tangent (tanδ) of 0.0009 and dielectric constant (ε_r) of 2.2. A DGS-based ring slot microstrip antenna is simulated, tested and experimentally characterized on different body locations (leg, chest, and hand) along with bending, and their results are presented accordingly. The magnitude of S₁₁ (|S₁₁|) of the proposed antenna is -26.81 dB at resonant frequency of 3.45 GHz, with the impedance bandwidth of 22 MHz (3.486 GHz to 3.508 GHz), peak gain of 6.27 dBi, and radiation efficiency of 85.02%. The simulated specific absorption rate (SAR) for 1 g and 10 g human body tissues is 0.263 W/Kg and 0.076 W/Kg, respectively. The total volume of the antenna is 0.58λ₀ × 0.58λ₀ × 0.00595λ₀ (at 3.5 GHz). The proposed antenna is suitable for 5G wearable devices.

This study presents an aperture-coupled slot-fed antenna specifically designed to operate in two frequency bands. It functions seamlessly within the 5.2-5.3 GHz and 5.9-6.1 GHz ranges, featuring unique characteristics: emitting monopole radiation at lower frequencies and transitioning to a broadside pattern at higher frequencies. The 5.2-5.3 GHz band is primarily used for high-speed Wi-Fi (IEEE 802.11 standards) and small cells in 5G networks, as well as radar systems. The 5.9-6.1 GHz band supports Intelligent Transportation Systems (ITS), vehicle-to-everything (V2X) communication, and C-band satellite uplink services. With a peak gain of 6.025 dBi, this compact antenna measures 25 mm × 25 mm × 1.6 mm (0.492λ × 0.492λ × 0.0315λ, where λ is the wavelength calculated at 5.9 GHz) and is precisely printed on two FR4 substrates, ensuring both performance and practicality. Thorough measurements of the constructed prototype show a remarkable alignment between simulated and measured results, confirming the antenna's reliability and precision. Its distinctiveness lies in its engineered adaptability, perfectly suited for applications requiring diverse patterns within dual-band scenarios. This adaptability allows for flexible signal reception, making it an ideal choice for situations demanding robust performance across multiple frequency ranges. Given its ability to offer varied pattern configurations, this antenna shows significant promise for applications where flexible and reliable signal reception is crucial.

This paper introduces a compact dual-band circularly polarized (CP) slot antenna utilized for L-band Global Navigation Satellite Systems (GNSS) applications. The designed antenna structure is a printed L-shaped slot antenna (PLSA) fed by coplanar waveguide (CPW) with a squared ground plane. An L-shaped feeding line is protruded into an L-shaped slot to achieve a circular polarization operation. A reversed T-stub is adopted near the right center of the radiating patch in order to achieve a dual-band operation. The achieved fractional impedance bandwidths (FIBWs) are 5.6% (1.21-1.28 GHz) and 12.2% (1.46-1.65 GHz). The fractional axial ratio bandwidths (FARBWs) are 8.0% (1.21-1.31 GHz) and 18.0% (1.42-1.70 GHz) for the lower and upper GNSS ranges, respectively. The suggested antenna provides right-hand circular polarization (RHCP) radiation. The gain of the suggested antenna ranges between 3.0 dBic and 3.2 dBic for the lower and upper GNSS bands, respectively. The designed antenna exhibits a dual-band behavior that covers both the lower and upper GNSS bands. It has a low profile of 55 × 55 × 1.524 [mm]³ (0.22λ₀ × 0.22λ₀ × 0.006λ₀), which makes it suitable for incorporating within any portable devices receiving GNSS signals. The antenna is lightweight, small in size, simple structure, inexpensive, high FARBW, high FIBW, and demonstrates CP dual-band behavior with a single input. The antenna is simulated, fabricated, and measured. The measurements verify the numerical results successfully. The suggested antenna is suitable for GNSS applications due to its enhanced performance.

Antennas operating in the close vicinity of obstacles or scatterers behave much different from isolated antennas radiating in free space. To assess such interactions in which a large number of parameters are involved (pertaining to the geometry, possible movement effects, and materials), stochastic models are often conceived and adopted so as to cope with innate uncertainties and to overcome the need for time-consuming parametric investigations. In this paper, an analytical stochastic approach is presented for the archetypical problems of the vertical, horizontal, and arbitrarily oriented dipole above a semi-infinite ground (either perfectly conducting or dielectric). The analysis focuses on how the input impedance of the dipole is affected by the existence of the ground plane when the distance or the angle between them varies in accordance with some certain probability distributions. Approximate closed-form expressions are obtained for the probability distributions of the input resistance and reactance separately, which can directly yield the respective moments and variances (and potentially other quantitative measures) and are useful for characterizing the probabilistic behavior of the dipole and its interaction with the ground. Representative numerical results are presented aiming at the validation of the proposed model and the investigation of the probabilistic behavior of the impedance change. Finally, a few concluding remarks are outlined, and possible extensions to real-world problems are discussed.

Dual-modality tomography integrates two different imaging technologies, allowing for the acquisition of more comprehensive sensing data. By combining information from both modalities, the accuracy of final imaging results is enhanced. However, due to the use of different physical sensitive field backgrounds by different measurement modalities, integrating information from different modalities with differing dimensions presents a challenge. To address this issue, a supervised DSCTFusion-ECA deep learning method is proposed. This method consists of four modules: initial imaging, feature extraction, feature fusion, and image reconstruction. In the feature extraction module, dense connections are utilized first to extract shallow cross-modal features, then two dual-branch feature extraction networks are utilized to separately capture modality-specific low-frequency global features and high-frequency local features for both modalities. The performance and robustness of multi-modality tomography can be effectively improved through the extraction of more comprehensive features. In the feature fusion module, Efficient Channel Attention is employed to capture channel dependencies and generate attention weights. The modal complementarity and the representation ability of key features have been enhanced, while avoiding information redundancy, thereby improving the discriminative power of the features. Simulation results show that the proposed network can fully extract and fuse features from EMT and UTT modalities, demonstrating strong robustness and generalization. Compared to the widely used U-Net network in tomography, DSCTFusion-ECA yields better reconstruction results.