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.

A miniaturized ultra-wideband (UWB) antenna with quadruple reconfigurable characteristics is proposed in this paper. The first step involves the development of an elementary circular patch antenna of size 28.5 × 28.5 mm², which is subsequently modified to demonstrate UWB properties. To incorporate quad-band notch features, the radiating surface of the patch antenna is etched with four inverted U-shaped slots. The antenna has an impedance bandwidth ranges from 3.1 GHz to 12 GHz, with four specific notches located at 3.62 GHz (3.46-3.69 GHz), 3.94 GHz (3.81 GHz-3.94 GHz), 4.3 GHz (4.19 GHz-4.39 GHz), and 4.84 GHz (4.61 GHz-5.05 GHz). By incorporating four PIN diodes, the antenna is capable of attaining a range of sixteen reconfigurable states across the UWB spectrum. The design of this system successfully addresses the issue of interference caused by WiMAX, satellite communication uplink C-band, Indian national satellite system, and WLAN. The prototype was constructed and evaluated, with the results from simulation and measurement correlating well.

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.

A metalized through-hole perturbation structure is proposed to effectively control multiple modes of substrate-integrated waveguide (SIW) filters. The method manipulates six modes (TE₁₀₁, TE₂₀₁, TE₁₀₂, TE₂₀₂, TE₃₀₁, and TE₄₀₁) result in the formation of three passbands. Subsequently, two symmetrical parallel complementary split ring resonators (CSRRs) are introduced without altering the filter's size. These rings generate resonances primarily excited by TE₂₀₁ and TE₁₀₂, allowing the filter to produce a fourth passband. Additionally, extra transmission zeros (TZs) are added, creating a perturbing effect on other modes. This further aids in controlling the resonances of these modes. The filter exhibits flexibility and controllability in terms of center frequency, bandwidth, and transmission zeros. The center frequencies of the four passbands are measured at 7.47 GHz, 9.84 GHz, 11.02 GHz, and 12.65 GHz, with return losses exceeding 18 dB. Additionally, there are six TZs, with the highest frequency point reaching -56.58 dB, indicating good in-band and out-of-band rejection. The measured and simulated results demonstrate satisfactory performance and applicability to multi-channel transmission in radar and satellite communication systems.

In this paper, a high-selectivity differential filtering quad-frequency antenna is proposed, consisting of two pairs of parallel enhanced folded dipoles and a diplexer. The diplexer employs unbalanced-to-balanced feeding, enabling the desired frequencies and transmission zero points by adjusting the lengths and distances between the stepped impedance resonators. Moreover, enhanced folded dipoles are arranged on either side of the substrate, which can feature a more compact structure and achieve multi-band radiation performance. For verification, a prototype of the proposed differential filtered quad-band antenna is fabricated and measured, having a size of 80 mm × 94.2 mm × 1 mm (1.10×1.29×0.0137λ_g at 2.53 GHz). Measured results show that the relative impedance bandwidths with |S₁₁| < -10 dB at the center frequencies of 2.53, 2.89, 3.30, and 3.68 GHz are 1.97%, 1.00%, 2.25%, and 2.04%, and the corresponding gains are 4.56, 2.82, 3.93, and 3.43 dBi, respectively, revealing its stable radiation performance and excellent anti-interference ability.

Due to the presence of finite ground, the radiation pattern of a monopole antenna will upwarp, thereby affecting the communication quality in the horizontal direction. Loading parasitic metal pillar elements near monopole antenna is a common beam control method. In this paper, an inverted monopole antenna is used as the source antenna to analyze the effect and band of beam upwarping suppression in wide band. The working principle and parameter analysis of elements are also discussed. This antenna can achieve 1-24°of suppression from 360 to 570 MHz. At the same time, keeping the un-roundness almost unchanged, the horizontal plane gain is increased by 0.53-1.74dB. The omnidirectional pattern is improved, which provides a valuable candidate for vehicle communication.

In the field of wireless power transmission (WPT) for electric vehicles, the challenge of magnetic shielding technology is particularly prominent. Achieving effective magnetic shielding often comes at the cost of transmission efficiency, creating a significant technical bottleneck. As a result, research into improving transmission efficiency while minimizing magnetic leakage has become a primary focus in the industry. This is seen as critical for driving the sustainable development of the electric vehicle sector. In response to this challenge, this paper presents the construction of an active magnetic shield using an isotropic coil configuration, which not only optimizes system efficiency but also significantly reduces magnetic leakage in WPT systems. The paper begins by introducing the concept of an active magnetically shielded isotropic coil structure for wireless power transmission. Next, it details the design methodology and operational principles of the structure, followed by the derivation of the mathematical model and equivalent circuit. The effectiveness of the magnetic shielding mechanism is examined from a theoretical standpoint, and the influence of coil parameters on both shielding performance and transmission efficiency is analyzed. Finally, based on the optimized coil parameters, the design of the wireless charging system incorporating the magnetic shielding structure is completed. This includes relevant theoretical calculations, simulation analyses, and experimental validation to confirm the feasibility of the design. The results demonstrate that the active magnetically shielded isotropic coil significantly reduces magnetic leakage, lowering it by approximately 95.68% compared to traditional coils, while achieving a transmission efficiency of 95.68% in experiments.

In this paper, two new types of dual-band antennas are presented: a coplanar waveguide (CPW)-fed fractal monopole antenna (FMA) and an asymmetric coplanar strip (ACS)-fed fractal half-monopole antenna (FHMA). These antennas are designed to operate in two distinct bands suitable for 3.5/5.5 GHz WiMAX and 5.2/5.8 GHz WLAN applications. Both antennas possess the property of self-similarity by employing half- and quarter-circular folded loops, respectively, which represent the antennas' radiating elements. A design procedure based on a conventional circular patch antenna (CPA) is performed, with evolution steps leading to the achievement of the proposed two antennas with the above-mentioned features. To validate the design concept, two simulator programs (CST MWS and HFSS) were used to extract the simulated results regarding reflection coefficient S₁₁, gain, efficiency, and radiation patterns. According to the agreement between the CST and HFSS simulated results, prototypes of the FMA and FHMA are fabricated on an FR4 substrate with a dielectric constant of 4.4, a height of 0.8 mm, and overall sizes of only 26×20 mm² and 12×19 mm², representing nearly 73% and 40% reduction in size, respectively, compared with the size of 26×33 mm² for the CPA. The simulated and measured S₁₁ results are in good agreement, illustrating the two antennas operating over the desired bands (S₁₁ ≤ -10 dB): 3.5-/5.5-GHz (3.40-3.69 and 5.25-5.85 GHz) WiMAX and 5.2-/5.8-GHz (5.15-5.35 and 5.72-5.85 GHz) WLAN. Furthermore, the peak realized gain values are greater than 2 dBi, efficiency exceeding 90%, and nearly omnidirectional radiation at both bands. Based on the achieved results and antennas' compactness, they can be highly recommended for the use in WLAN and WiMAX applications.

This paper presents a dual-band cascaded rectangular microstrip patch antenna array with a complementary split ring resonator (CSRR) for narrow-band wireless communication applications. The antenna array is fed with a microstrip feed line for proper impedance matching, and CSRR is loaded to generate dual-band characteristics. The CSRR-based proposed antenna radiators operate over two frequency bands, i.e. 100 MHz (3.06-3.16 GHz) and 110 MHz (4.36-4.47 GHz) with reflection coefficients (S₁₁ < -10 dB) of -23 dB and -32 dB. The gain of the proposed antenna array with CSRR is 5.03 dBi and 6.34 dBi at 3.1 GHz and 4.4 GHz respectively. In addition, S-parameters, radiation patterns, 3D gain characteristics, and surface current distribution at resonating frequencies are observed. The proposed antenna array is miniaturized in size and suitable for wireless communication applications.

The paper presents the results of numerical modeling of the compression of a frequency-modulated electromagnetic pulse in a straight waveguiding defect of a finite two-dimensional photonic crystal. For the first time, the time reversal method was used to accurately compute the temporal profile of a current pulse that excites an electromagnetic wave that is being compressed in such a structure, given that its temporal profile (electric field intensity) has a specified shape at a given point in space. The photonic crystal consists of an array of sapphire bars with a square cross-section of 1 mm × 1 mm, arranged in free space at a distance of 1 mm from each other. In this model, the boundaries of the frequency range containing the crystal's band gap (from 35.6 to 46.5 GHz), the optimal width of the waveguiding defect (4 mm), and the shape of the excitation current pulse for the waveguiding defect with a length of 0.5 m were found. The obtained pulsed power amplification coefficient is approximately 7.48. A photonic-crystal analog of an H-plane horn antenna was used to radiate the compressed pulse into free space.

This work presents a new negative resistance self-oscillator based on an integrated active antenna and InGaAs HEMT technology, specifically designed for Internet of Things (IoT) applications. A key aspect of this design lies in the series integration of the active circuit and the antenna patch. The fabrication and testing were carried out on an FR4 substrate with a thickness of 0.8 mm. The Harmonic Balance numerical method, implemented in the Advanced Design System tool, was used for the optimization and co-simulation of the system. After simulation and measurement, the proposed self-oscillator, with a compact size of 3.4 x 3 cm², produced very significant results. The simulated output power reached 12.87 dBm at a frequency of 3.07 GHz, while the measured output power was 12.85 dBm at 3.04 GHz, with a recorded phase noise of -78 dBc/Hz at 10 MHz. The qualitative and quantitative performance of the proposed self-oscillating antenna makes it particularly suitable for applications such as satellite mobile communications, GPS, telemetry, and telemedicine.

A dual-band MIMO antenna with high isolation is designed in this paper for coal mine applications. Each of the two elements in the designed MIMO antenna is composed of a bident-shaped monopole structure which is designed to cover the 5G NR frequency region (2.51-2.67 GHz, 3.4-3.6 GHz) allocated for coal mine scenario. The two elements are symmetrically placed to achieve high isolation at lower frequency region with an element spacing of 0.09λ at the lowest operating frequency. To further reduce the mutual coupling between the two elements, the decoupling network technique is utilized. In particular, a neutralization line is loaded with an adjustable capacitor and two adjustable inductors on the ground. In this way, an isolation of higher than 20 dB is achieved over the two operating frequency bands for the MIMO antenna, i.e., the isolation is increased by more than 11 dB and 10 dB for the lower and higher bands, respectively. Besides, the good performance of the designed MIMO antenna in terms of correlation values and diversity gain makes it a suitable candidate for 5G MIMO applications under coal mine scenarios.

Although initial results for the digital implementation of non-Foster impedances showed promise for increasing the bandwidth of electrically small antennas beyond the Chu limit, earlier approximate design methods were inadequate to fully describe the complexity of digital impedance circuits. Recently, the input impedance of such digital impedance circuits was discovered to be dependent on the external source impedance of the driving source. Furthermore, this dependence on the driving source impedance was shown to be extraordinarily complicated, even for a purely resistive driving source. Consequently, the digital non-Foster impedance match of an antenna is considerably more complicated, even with a lumped-element antenna model. In this paper, we present a method for designing a stable wideband digital non-Foster circuit to match the impedance of an electrically small dipole antenna. Simulation results confirm the theoretical predictions and the efficacy of the design method in producing VSWR bandwidth beyond the Wheeler-Chu limit. An RLC model of a 10 MHz electrically small dipole with Q of 215 and passive-tuned bandwidth of 46.5 kHz is chosen to demonstrate the proposed method. For this antenna with Wheeler-Chu bandwidth limit of 442 kHz and size parameter ka = 0.42 rad, the proposed method results in achieving an impedance bandwidth of 2.3 MHz, or more than five times the Wheeler-Chu limit and 48 times the passive-tuned bandwidth. Lastly, the mid-band noise figure is 12.7 dB when the proposed design is combined with a receiver having 3 dB noise figure.

Motor energy efficiency has gradually become a research hotspot. In this paper, the optimization analysis of motor energy efficiency is carried out for the widely used three-phase induction motors. Based on keeping the stator and rotor structure parameters unchanged, a reasonable combination of motor steel material, winding type, and bar conductor material can realize the change in motor energy efficiency class. Firstly, the influence of stator and rotor steel materials on iron consumption is analyzed using the triple equation of iron consumption. And the loss distribution and efficiency of DW540, DW470, DW360, DW310, DW270, 1J22, and amorphous alloy materials are discussed. Secondly, the effect of different winding types on the no-load reverse electromotive force is analyzed and discussed, and its simulation model is constructed. The corresponding motor efficiency is summarized. Then, the impact of cast copper and aluminum rotors on energy efficiency is compared and analyzed. Finally, the steel material combinations, winding type, and bar conductor material are classified according to the IE3, IE4, and IE5 energy-efficiency classes. The results show that by choosing the right combination, the motor's energy efficiency can be increased by up to 95.3%.

The rotor of PMa-BSynRM, with its multi-layer barriers and permanent magnet, poses a challenge in the design process as both torque system and suspension force system performance need to be considered comprehensively. To solve this problem, a multi-objective optimization method for the rotor structure of PMa-BSynRM is proposed in this paper. Firstly, the harmonic characteristics of PMa-BSynRM air gap magnetic field are analyzed based on the magnetic potential and magnetic permeability method. The expression for suspension force under the coupled magnetic field is derived by combining Maxwell tensor method. This analysis reveals the relationship between magnetic field characteristics and suspension force, providing guidance for subsequent optimization design. Secondly, through the analysis of the rotor structure, the macroscopic parameters related to the micro and detailed geometric optimization of the PMa-BSynRM rotor are proposed. Based on these macroscopic parameters, the response surface method and dual-population-based co-evolutionary algorithm (DPCA) are applied to realize a compromise among the optimization objectives. Finally, the proposed optimization method is comprehensively analyzed through simulation analysis and prototype experiment. The simulation and experimental results demonstrate a reduction of 51% in optimized torque ripple and 74% in suspension force ripple, as well as a decrease of 3.2˚ in the suspension force error angle. After optimization, the performance of the motor torque and suspension force system is significantly improved, thus verifying the effectiveness and superiority of the proposed optimization method.

This research work investigates the performance of a novel low profile 20-bit frequency coded L-shape slot loaded resonator for chipless RFID applications. The proposed chipless RFID comprises a CPW-fed UWB radiator and an L-shaped multi-slot resonator to achieve 20-bit data capacity. CPW technique is implemented to enhance antenna bandwidth and radiation characteristics. The designed UWB radiator covers the entire band from 3 to 12 GHz with better return loss. Also, the peak gain is measured as 6 dBi in the respective frequency spectrum. The proposed L-shaped frequency-coded multi-slot resonator is developed with a compact size of 23.6×14.1×1.6 mm³. Moreover, the frequency coding technique allows for a wide range of frequency combinations for data representation, as well as contributes to reducing the RFID tag size. The research holds significance in propelling RFID technology forward and ushering in a new era of small, efficient, and flexible data encoding solutions.

A compact and tunable ultra-high frequency (UHF) radio frequency identification (RFID) tag antenna is proposed. The antenna comprises a rectangular ring, two symmetrical radiating arms formed by multiple L-shaped stubs, and two interdigitated structures. By adjusting the parameters of double interdigitated structures, the resonant frequency of the antenna can be tuned coarsely and finely, while maintaining a nearly constant maximum power transmission coefficient. The proposed tag antenna has a size of 28 mm x 16 mm (0.086λ x 0.049λ at 920 MHz). Measurement results show that the proposed antenna can achieve the maximum reading distance of 6.8 m at 920 MHz under the condition of 3.28 W effective isotropic radiated power. The proposed RFID tag antenna offers several advantages, including compact size and frequency tunability, making it well-suited for various RFID system applications.

Radially embedded probe-fed circular disc dielectric resonator antenna (DRA) for ultrawideband applications is investigated. Initially, a single-layer probe fed DRA is developed. The probe length is adjusted to optimize S11 performance. For a probe length of 10 mm, a measured -10 dB bandwidth of 47.8% (4.75-7.74 GHz) is obtained. The design is modified with two concentric rings of different dielectric materials with a hollow center. The modified configuration improves the matching from an S₁₁ value of -18 dB at 5.23 GHz to -24.2 dB at 4.56 GHz. However, the measured -10 dB bandwidth reduces to some extent to 38.4% (4.2-6.2 GHz). In another modified design, an air gap is introduced between two inner discs of Alumina supported by a solid outer ring of Teflon. The radially embedded feeding probe, therefore, protrudes into the circular air pocket sandwiched between the two Alumina discs. An improved measured bandwidth of 55.9% (6.66-11.83 GHz) is obtained. Measured S₁₁ of -24.1 dB is similar to that obtained for the concentric ring design but at a higher frequency of 9 GHz. All the three antenna designs feature a reduced size having a volume of approximately 1963.5 mm³, wider bandwidth and consistent radiation pattern over the operating frequency band. It makes the proposed designs suitable for ultra-wideband (UWB) applications.