In the past few years, deep learning has emerged as a transformative force in tackling challenges within the realm of electromagnetic inverse scattering, driving remarkable advances and reshaping conventional approaches. Among them, the physics-assisted learning method that combines traditional inverse scattering algorithms with deep neural networks has demonstrated excellent real-time inversion capability and lower computational complexity. For two-dimensional inverse scattering problems, an approximate solution of the target is first obtained using a linear approximation algorithm, followed by mapping learning from low to high precision with a neural network. To enhance both precision and generalizability, this study integrates a Transformer module into a CBAM U-Net framework, giving rise to a refined architecture aptly named TransAtten U-Net. By retaining certain positional information while enhancing the correlations between features, the overall feature extraction effect is improved. Through simulation experiments, the paper compares the performance of the proposed TransAtten U-Net two-step method, TransAtten U-Net direct method, and CBAM U-Net two-step method. Experimental results demonstrate that the proposed TransAtten U-Net two-step method not only achieves higher accuracy than the other two approaches, but also exhibits a stronger generalization capability across diverse scenarios, along with enabling real-time imaging.

This paper proposes a single-port microwave sensor for solid material characterization, based on defected ground structures (DGSs) with complementary split-ring resonators (CSRRs). Fabricated on an RO5880 substrate, the sensor was analyzed through both simulation and experimental measurement. Electromagnetic simulation and optimization were conducted using CST Studio Suite within the 1.5-3.0 GHz frequency range. The sensor's performance was evaluated with three materials of known permittivity: RO5880, RO4350, and FR-4. Results show that the two proposed configurations, one with a DGS CSRR (Design A) and the other with an added slot on the DGS CSRR (Design B) yielding Q-factors of 332 and 357, respectively. The higher Q-factor in Design B indicates increased sensitivity across all tested materials compared to Design A. For example, Design B achieved the highest sensitivity of 4.71% for RO5880 material compared to Design A. Thus, the added slot enhanced field coupling, improving measurement sensitivity and confirming the sensor's suitability for microwave-based solid material characterization.

An analysis of electromagnetic scattering by multi-story, multi-window buildings is presented by utilizing the Kirchhoff Approximation method. This investigation specifically analyzes scattering characteristics for vertically polarized incident plane waves. Scattering fields are calculated via radiation integrals associated with equivalent current sources induced on the building's exterior and across virtually closed window apertures by the incident wave. Fields within window regions are represented using rectangular waveguide modes, enabling the conversion of reflected fields from window glass into equivalent currents. The formulation's validity is established through comparisons with the physical optics method and scale model measurements. Discussions address the influence of window glass and polarization on wave propagation in wireless communication scenarios like 4G LTE operating at 700 MHz.

Use of a small radiating loop (12 cm diameter) is recommended in EMC standards (Mil-Std-461G:2015(RS101) and IEC 61000-4-39:2017) for immunity testing with low-frequency magnetic fields. We investigated the limitations of this method using finite-element simulations. We studied the effects of fields from radiating loops with different radii and their induced voltages in different diameter receiver loops that represented wiring of equipment under test (EUT). We also studied the windowing-method recommended in those standards. It involves positioning the loop successively over all locations on each face of the EUT. Our results show that this radiating loop can only simulate exposure to larger real-world EM fields when the EUT's wiring area is smaller than the radiating loop. Another limitation is that the magnetic field from the radiating loop drops significantly with distance perpendicular to the loop surface. Therefore, the windowing-method with a small radiating loop is only suitable for simulating exposures to real-world sources with fields that do not extend a large distance from the loop. In addition, the field distribution (width and depth) of the real-world EM source must be accounted for before deciding to use a small radiating loop for immunity testing of an EUT.

This work is motivated by the recently domination of mobile and wireless communications technologies, in addition to the fast evolution of the new generation of mobile and wireless communication that leads to the successive mobile generations XG 3G, 4G, 5G, and in near future 6G. Currently, the fifth generation (5G) technologies still need more development for a compact and efficient device. In this manuscript, Meta cells units (metamaterial and metasurface) are employed for improving the main parameters of antenna performance like gain (G), bandwidth (BW), reflection coefficient ($S_{11}$), and radiation efficiency. The proposed antenna design shows multiple resonant frequencies which means that the design is able to operate at multiband of frequencies, including 6\,GHz band that considers the main targeted band of 4G and 5G mobile communication technologies. The simulation results, for the different models via adding meta cells to the proposed design model, show excellent improvement for the performance parameters that are improved excellently in comparison with the conventional circular patch (CCP) and previous literature. In addition, the use of meta cells reduced the resonant frequency which means that it can serve a lower frequency with small size of substrate, and it is half size of CCP, making it suitable for many applications that require a compact antenna design.

In this paper, a Quadband Octagon Patch Antenna is designed whose operating frequencies are 20.22 GHz, 23.64 GHz, 27.35 GHz, 28 GHz, 28.37 GHz which achieved return losses of -19.67 dB, -19.14 dB, -19.66 dB, -19.04 dB, -19.04 dB, -20.41 dB and gain of 6.1 dB, respectively. The substrate employed in this antenna is FR4, which features a dielectric constant value 4.4 and a loss tangent value of 0.002. With a radiation efficiency of 90.85%. This antenna is small, measuring only 15 × 25 × 1.6 mm³ dimensions. Multiple slots of different lengths are inserted in an antenna to form a 5G Quadband Octagon Patch Antenna in order to accommodate more operating frequencies. Later, a 2*2 MIMO octagon patch antenna having a 3.6 mm radius, 50 × 30 × 1.6 mm³ of dimensions, 4.4 dielectric constant, and 1.6 mm thickness with defective ground structure is designed. Here this single quad band antenna was turned to a broadband MIMO antenna by means of a defective ground structure.

This paper presents a compact multiple-input multiple-output (MIMO) microstrip antenna system covering the 2.4 GHz and 5 GHz wireless local area network (WLAN) bands. By etching rectangular slots on the microstrip patch and adjusting the dimensions of both the antenna and the rectangular slots, the antenna system can radiate at the operating frequencies of 2.44 GHz and 5.3 GHz simultaneously. To achieve high port isolation across the two distinct WLAN bands, a ``WM''-shaped defected ground structure (DGS) is etched on the ground plane to reduce mutual coupling in the 2.44/5.3 GHz frequency bands. Simulation results demonstrate that within the frequency ranges of 2.41-2.49 GHz and 5.22-5.39 GHz, the isolation of the two dual-band antenna systems achieves maximum coupling suppression of 26.7 dB and 14 dB, respectively. This DGS can serve as a potential solution for decoupling in WLAN MIMO antennas.

This research offers a 12-element antenna array optimized for MIMO utilization in fifth-generation (5G) mobile phones. The antennas operate in the sub-6 GHz long-term evolution (LTE) frequency range, specifically between 3.4 and 3.6 GHz. To fulfil the growing demand for faster data speeds and reliable connection in 5G networks, the presented MIMO antenna setup offers a balance between compact size and high performance, making it well suited for integration into smartphones. Every radiating element in the array is tuned to approximately 3.5 GHz and features an open-slot structure, which effectively reduces mutual coupling and enhances isolation. Antenna arrangement has been constructed on an FR-4 substrate of dimensions 150 mm × 80 mm × 0.8 mm, corresponding to the layout restrictions of standard 6-inches smartphones. A prototype was developed to validate the design through measurements. The results demonstrate excellent impedance matching (return loss > 10 dB), high isolation (> 20 dB), strong radiation efficiency (exceeding 66%), and a low envelope correlation coefficient (< 0.03) covering the target frequency range.

In this paper, machine learning supports a compact electromagnetic band gap structure (EBG) based dual band microwave sensor which is proposed for dielectric characterization of liquids with high sensitivity. Two edges, located via metalized holes, are electrically coupled with a suspended microstrip line. Two channels are placed in the electric field region of each EBG patch. Therefore, the change in frequency shift and quality factor are observed, which will help to describe the dielectric characterization of Liquid Under Test (LUT). A matrix-based mathematical model, and machine learning based prediction model are developed for the calibration and validation of the sensor. The results are experimentally verified through fabricated prototype for the binary mixture of water and ethanol. The proposed sensor achieved a compactness with size of 0.164λ_2.47GHz × 0.164λ_2.47GHz, an average sensitivity of 0.931, 0.243, and a quality factor of 170, 230 for band-1 and band-2, respectively. The calculated dielectric constant of different samples shows good agreement with the values reported in the literature. The machine learning based model is developed using the Support Vector Regression algorithm and achieves the high value of coefficient determination (R²) which is 99.01, and the less root mean square error (RMSE) value is 0.009.

To address the problem that the control performance of permanent magnet synchronous motor (PMSM) in model predictive torque control (MPTC) is highly sensitive to motor parameters, an improved model predictive torque control scheme for PMSM based on anti-stagnation particle swarm online parameter identification (ASPSO-IMPTC) is proposed. First, an improved MPTC strategy based on inductance and magnetic chain parameter compensation is proposed. Compared with conventional MPTC, the proposed method can acquire accurate motor parameters in real-time, thereby enhancing both the control performance and parameter robustness of PMSM. Second, a review mechanism is proposed to enhance traditional PSO parameter identification. This method prevents particle swarm stagnation, enhances the parameter identification ability of the traditional method, and improves the real-time accuracy of the motor parameters. The parameter robustness of the motor is further enhanced. Finally, the experimental results show that the proposed ASPSO-IMPTC strategy can effectively improve the control performance and parameter robustness of PMSM when parameters mismatch occurs in PMSM.

In this paper, a racket-shaped ultra-wideband (UWB) multiple-input multiple-output (MIMO) antenna is analytically designed using characteristic mode analysis. The antenna has an overall size of 60 × 60 × 1.6 mm³ and consists of four racket-type radiating elements, four ground planes shaped like the number 6, and a cross-shaped decoupling structure between the radiating units. In the single antenna configuration, the feed position is determined by analyzing the current and electric field distributions of its characteristic modes. The bandwidth and current distribution are optimized by integrating seven small rings, L-shaped branches, and etched slots to ensure the simultaneous excitation of six characteristic modes, thereby enabling its UWB performance. In the MIMO setup, four elements are orthogonally arranged, and a cross-shaped decoupling structure along with a defected ground structure is employed to reduce mutual coupling, achieving over 20 dB isolation between any two elements. Simulated and measured results confirm that the antenna operates over the 3-21 GHz range, fully encompassing the UWB range of 3.1-10.6 GHz. Furthermore, the antenna achieves up to 77% radiation efficiency, a peak gain of 5.75 dBi, and a low envelope correlation coefficient (ECC).

In this paper, a compact multiple-input multiple-output (MIMO) antenna is proposed for unmanned aerial vehicles (UAVs). By simultaneously exciting common mode (CM) and differential mode (DM) from a T-shaped slot, wideband coverage is achieved. Four such slot antennas are used to form a four-antenna module operating in the N79 band (4.4-5.0 GHz). The size of the four-antenna module is merely 43 × 8 mm², demonstrating excellent miniaturization and integration. The dominant coupling between adjacent elements occurs through currents of the same mode. When CM and DM currents coexist, partial cancellation of coupled currents at the feed point enables high isolation without ex-ternal decoupling structures. Two modules are symmetrically positioned along the longer edges of the frame, forming an 8-element MIMO antenna. The antenna achieves isolation greater than 11 dB and an envelope correlation coefficient (ECC) below 0.04. The measured total efficiency is better than 52%, with an average of 56%. Featuring compact footprint, zero-clearance constraint and high isola-tion, the proposed antenna is a promising candidate for 5G UAVs.

Aiming at the issues of large current ripple and significant torque pulsation in switched reluctance motor (SRM) model predictive current control (MPCC) under varying operating conditions, this paper innovatively proposes a novel SRM model predictive current control method integrating an Extended State Observer (ESO) and the Lehuy model. By constructing a nonlinear current prediction framework based on the Lehuy model, the data dependency on traditional Look-Up Table (LUT) methods is significantly reduced. Meanwhile, the real-time compensation of system disturbances is achieved by introducing the ESO, resolving parameter mismatch issues under dynamic operating conditions. Simulated and experimental results demonstrate that this method, implemented on a 12/8-pole SRM prototype, achieves a current ripple reduction of 41.5% and torque pulsation suppression of 32.7% compared to traditional LUT-MPCC. This research provides new insights into the robust control of SRMs in high-precision servo scenarios.

This paper proposes a multistep reflector backing for compact spiral antennas to provide a consistent unidirectional pattern over a wide frequency band with improved gain, Axial Ratio (AR), and efficiency for 2-18 GHz applications. The effect of the variation of step number and step sizes of the reflector on antenna parameters has also been studied in the proposed work. The fabricated prototype antenna provides good impedance matching and circular polarization over the entire frequency range and is compact in size with a height of 0.078 wavelengths (λ_m) at lowest frequency. The antenna exhibits a rotating radiation pattern with frequency in azimuth direction providing almost a constant beamwidth of 117° with the variation in gain limited to only 0.75 dBic above 8 GHz, yielding a flat gain response at higher frequencies. The compact size and improved parameters of the designed wideband antenna with a stepped reflector makes it a suitable candidate for electronic warfare applications.

In this design, a wideband circularly polarized slot antenna loaded with square ring is designed and validated. The square slot antenna is etched on an FR4 substrate with the calculated dimensions at the resonant frequency of 5 GHz. The square slot antenna is truncated in its corners to obtain two degenerative modes which are orthogonal to each other, and they are required to produce circular polarization. The truncation is optimized to obtain the circular polarization. The wide CP bandwidth is achieved by selectively spacing the degenerative modes far in frequencies and loading the ring on the slot antenna. The ring and the truncated slot antenna dimensions are optimized to achieve broad axial ratio bandwidth. The design is fabricated and experimentally verified. The measured impedance bandwidth of 47.53% is achieved at the center frequency of 5.68 GHz. The measured axial ratio bandwidth of 39.27% is obtained at the center frequency of 5.55 GHz. The peak gain of the antenna is 3.8 dBi with variation of 1-2 dBi over the entire bandwidth. The simulated radiation efficiency of more than 80% is obtained in the entire bandwidth with a cross polarization level of -20 dB with respect to co-polarization. The proposed design is compact and best suitable for NR46, NR47, NR79, N102, and N104 bands of 5G and C band wireless applications.

This paper presents a novel and compact single-layer patch filtering antenna with excellent out-of-band rejection performance. The antenna adopts a simple structure consisting of a single-layer substrate, a slot-loaded radiating patch, and a ground plane, and is fed by a coaxial probe. The rectangular radiating patch and the ground plane are loaded with Г-, anti-Г-, and U-shaped slots to form the final design. The introduction of these slots successfully generates two resonance points, which extend the operating bandwidth. It also produces two out-of-band radiation nulls that enhance the out-of-band rejection performance. To validate the proposed design, antenna prototypes were fabricated and measured. The simulation and measurement results are consistent. The antenna exhibits stable realized gain and excellent bandpass response. It achieves a peak realized gain of 8.82 dBi, an impedance bandwidth of 12.8%, and out-of-band rejection greater than 21.26 dB. These characteristics make the proposed patch antenna highly suitable for various wireless communication applications.

This paper investigates the theoretical bounds of geometric dilution of precision (GDOP) in two-dimensional time difference of arrival (TDOA) positioning systems. The corresponding base station (BS) deployment for a single mobile terminal (MT) is subsequently derived. Considering the correlation of time difference measurements, a simplified closed-form expression for GDOP is first derived, and it is shown that GDOP is independent of the selection of the reference BS. Theoretical bounds for GDOP are rigorously established, along with the conditions under which these bounds are valid. Based on these boundary conditions, the study demonstrates that optimal deployment occurs when BSs are grouped, and the azimuths of BSs within each group are evenly distributed around a circle centered at the MT. For systems with up to five BSs, the optimal deployment is proven to be unique, whereas non-unique solutions emerge for larger configurations. In contrast, the complete solution set for the worst-case deployment occurs when BSs are collinear and symmetrically aligned along a specific coordinate origin or axis. Numerical simulations validate the theoretical findings, highlighting the superiority of uniform angular distributions. These results provide actionable guidelines for enhancing positioning accuracy in cellular networks and a foundational framework for multi-BS deployment optimization.

In this paper, a substrate integrated waveguide based self-quadplexing antenna with modified U-shaped slots is presented. The quadplexing antenna resonates at four distinct frequencies 4.02 GHz, 4.37 GHz, 4.78 GHz and 5.26 GHz by adjusting the length of U-shaped slots. The antenna shows a minimum port isolation of >34 dB between any two ports. The self-quadplexing antenna gives the frequency tunability and shows an unidirectional radiation pattern at the corresponding operating frequencies. The simulated (measured) gains of the antenna are 5.18 dBi (5.24 dBi), 5.51 dBi (5.57 dBi), 5.03 dBi (5.14 dBi), and 5.12 dBi (5.19 dBi). The proposed antenna is independent of frequency tunability by the excitation of four ports with an antenna size of 0.12 λ₀², where λ₀ is the free space wavelength at the lowest resonant frequency. These features make the proposed antenna suitable for WLAN, ISM, INSAT C, Wi-Fi applications.

A highly isolated MIMO antenna is designed using a neutralization line (NL), stubs, and slots for 5G, Wi-MAX, and WLAN operations. A quarter circular ring monopole is modified to have a circular outer shape and a polygon inner shape. Thickness of the monopole is reduced to decrease the electromagnetic (EM) coupling between the higher order modes and to obtain dual band characteristics. A two-element MIMO antenna is designed. High isolation is achieved by combining isolation techniques of neutralization line with stubs and slots. Isolation >20 dB is achieved with stubs and slots in ground plane. Without altering the overall dimensions, isolation is improved from 20 dB to 30 dB by using an NL in the MIMO structure that uses slots and stubs in the ground plane as isolation techniques. S₁₁ < -10 dB over 2.9-3.9 GHz and 5.6-6.2 GHz and S₁₂ < -30 dB over 3.3-3.9 GHz, and S₁₂ < -40 dB over 5.6-6.2 GHz covering 5G, Wi-MAX, V2X, and WLAN bands are obtained. The antenna has stable radiation patterns. ECC (Envelope Correlation Coefficient) < 0.002, DG (Diversity Gain) close to 10 dB, and MEG (Mean Effective Gain) about 0 dB satisfy MIMO specifications. The compact, low-cost antenna on a 30 × 50 mm FR4 substrate is simple to design and fabricate. These features make it a suitable candidate for 5G, Wi-MAX, and WLAN applications.

The rapid development of wireless technology has increased interest in multiband reconfigurable antennas, especially as devices and satellites move toward miniaturization. Reconfigurable antennas must be capable of adapting to their environment by dynamically altering their operating frequency, polarization, and/or radiation pattern. The fifth generation (5G) of wireless communication represents a significant advancement over 4G networks, aiming to meet the growing demand for data and connectivity in today's digital world. To achieve the performance required for supporting a wide range of use cases across both local and global markets, 5G must integrate various existing communication technologies. This work presents a multiband double T shaped frequency reconfigurable antenna for 5G wireless communication on a Rogers RT5880 substrate, designed and simulated using the CST Microwave Studio. In this antenna, two MA4SPS402 PIN diodes are used to make the antenna reconfigurable. By using these PIN diodes, the antenna works on four different modes based on both the diodes ON/OFF conditions. By using this configuration of the PIN diodes, the presented antenna operates at five different operating frequencies 10.8 GHz, 16.47 GHz, 17.03 GHz, 17.07 GHz and 21.2 GHz. The presented antenna provides the best reflection coefficient |S₁₁| value which is -24.76 dB at 21.2 GHz, and peak gain is 7.81 dBi at 16.47 GHz. The measurements of the fabricated antenna are done using a Vector Network Analyzer (VNA) and an anechoic chamber, confirming its reflection coefficient (|S₁₁|) and gain, making it a reliable option for 5G applications.