In this paper, we present our measurements about 3D printable microwave absorber materials. First, we determined the electromagnetic parameters of the material using different measurement techniques, whose some examples we present. Knowing the material parameters, a geometry for a 3D printable absorber was selected, and simulations were performed to optimise the geometry from X-band (8.2 GHz to 12.4 GHz) to Ka-band (26.5 GHz to 40 GHz). Pieces of absorbers were 3D printed using the optimised dimensions and were mounted to a metallic corner reflector as test subject. The corner reflector camouflaged in this way was then measured in an anechoic chamber, and measurements with and without the 3D printed absorbers are compared. We found good agreement between the measurements and simulations and found the structure and the material we used as usable candidates for the reduction of the radar cross section of an object.

The advancement of wireless communication technology demands antennas that can achieve significant gain while functioning across diverse frequency ranges. Numerous studies have aimed to enhance the gain and radiation properties of such antennas. However, when these antennas operate near the human body, their performance regarding return loss, gain, radiation pattern, and specific absorption rate (SAR) are influenced by the interaction and absorption of human tissue. To enhance overall antenna performance, artificial magnetic conductor (AMC) surfaces have been introduced. Numerous studies have been conducted to improve antenna performance through the use of AMC surfaces. This paper proposes a coplanar waveguide (CPW)-fed wearable antenna integrated with an AMC array. The integrated antenna is expected to operate at both 2.45 GHz and 5.5 GHz, making it suitable for applications in wireless local area networks (WLAN) and wireless body area networks (WBAN). The study focuses on the benefits of the integrated antenna, highlighting advantages such as improved gain and lowered SAR in comparison to the antenna alone. These improvements are validated through both simulated and measured outcomes. This antenna, featuring a simple feed structure, low cost, and ease of fabrication, is a promising option for wearable medical applications.

A phase-only and amplitude-phase genetic algorithm (GA) has been investigated to restore the array pattern of a 4 × 2 planar array in the presence of centre-elements phase malfunctioning. A single and double adjacent antenna elements are considered for phase malfunctioning. The new array weights for functioning antenna elements are computed with GA to restore the value of array peak gain and sidelobe level (SLL). The simulation results, which are verified with measurements, indicated that complete recovery of array pattern without SLL constraint in the presence of malfunctioning elements was possible with the phase-only GA weights. It is shown that the uncorrected pattern can also be compensated for main beam scanning with phase-only GA weights. However, pattern compensation with SLL constraint is not possible using the phase-only GA weights. Therefore, amplitude-phase GA weights are estimated to restore the peak gain and the desired SLL simultaneously at the cost of widening the main beam. A prototype of X-band 4 × 2 microstrip patch array controlled through X-band phaser evaluation boards was used in the in-house anechoic chamber measurements facility to validate the full-wave HFSS simulation results.

In this paper, a novel measurement matrix construction method based on adaptive cross-approximation (ACA) is proposed to improve the performance of the compressive sensing-based method of moments (CS-MoM) for analyzing electromagnetic scattering problems. ACA is based on a weight scheme and is able to recognize the rows and columns that contribute significantly to the matrix. Thus, the object is divided into multiple blocks, and the impedance matrix is partitioned into near-field and far-field groups to establish the condition for applying ACA. Then, the row indexes are extracted from the group with the highest number of ACA recognized rows in the far-field groups of each block. Finally, by combining all row indexes to extract the impedance matrix, a lower-dimensional and deterministic measurement matrix is constructed, thereby improving computational efficiency. Numerical simulation results validate the accuracy and effectiveness of the proposed method.

To address challenges such as low starting torque and inaccurate position estimation in traditional sensorless control methods for switched reluctance motors (SRMs), this paper proposes a sensorless control strategy suitable for the startup and low-to-medium speed operation of multiphase SRMs. Firstly, an improved inductance calculation model for the pulse injection region is proposed based on the electromagnetic characteristics of SRM. Secondly, leveraging the results of the inductance model calculation, a three-phase commutation rule is designed to enhance the starting capability. Lastly, an adaptive angle tuning (AAT) module is devised to improve the phase commutation width, and the pulse injection region is optimized through a dynamic inductance threshold method. The efficacy of the proposed method was validated through simulations conducted on a prototype six-phase 12/10 SRM.

Improving the efficiency of electrical machine is an important way to reduce carbon emissions. Accurate calculation and measurement of iron loss is an important part of improving efficiency of electrical machine. Therefore, how to accurately calculate and optimize the device structure to reduce iron loss has become a research focus. In this study, the influence of power supply, motor structure, ferromagnetic material, manufacturing processes and multiphysics on the motor iron loss is discussed and summarized. Then, the classification and summary of the existing iron loss models are discussed, and shortcomings and the future research direction are suggested. In addition, several induction motor efficiency measurement standards are described, and the defects and improvement direction of efficiency measurement of converter-fed motor are discussed. The contents discussed and summarized in this study can be helpful to engineers engaged in high efficiency motor design and motor driving algorithm development.

This article presents a groundbreaking approach to osteoporosis detection and monitoring by integrating a new wearable monopole antenna design with advanced machine learning algorithm (neural network). Inspired by the intricate pattern of a Christmas snowflake, the system utilizes UWB electromagnetic waves and bone attenuation analysis for compact, noninvasive, and highly accurate bone health assessment. Fabricated entirely from textile materials, the antenna features remarkable performance metrics, including an impedance bandwidth of 4.9 to 12.6 GHz and a reflection coefficient consistently below -10 dB, within a compact form factor of 41.9 mm × 29.2 mm. Experimental validation and comparative studies demonstrate the effectiveness of this approach in precisely classifying osteoporosis levels, achieving an outstanding accuracy rate of 87%. This study signifies a significant advancement in osteoporosis detection and diagnosis, combining state-of-the-art antenna technology with advanced machine learning techniques. The developed system holds promise for early detection and personalized monitoring of osteoporosis, contributing to improved healthcare outcomes and enhanced quality of life for individuals at risk of bone-related diseases.

The paper presents a model of an open resonator exhibiting a single high-Q eigen oscillation within a one-octave frequency band. The resonator is synthesized by integrating a diffraction radiation antenna, which comprises a segment of a dielectric waveguide above a metal substrate with a diffraction grating, into a system of flat reflectors aligned parallel to the wave fronts of surface and bulk waves generated by the antenna. A pulse response with an amplitude-frequency characteristic featuring one pronounced resonant maximum, which corresponds to an eigen oscillation with Q factor exceeding 10⁴, has been achieved in the proposed system. The optical length of the resonator exceeds the wavelength of the working oscillation by over 50 times. The feasibility of tuning the resonator via moving both the mirrors and the diffraction grating is demonstrated. The proposed model holds promise for applications in the development of solid-state and quantum radiation sources operating in the microwave and higher frequency ranges.

The integration of machine learning (ML) regression models in predicting the parameters of metamaterial antennas significantly reduces the design time required for optimizing antenna performance compared to traditional simulation tools. Metamaterial antennas, known for overcoming the bandwidth constraints of small antennas, benefit greatly from these advanced predictive models. This study applies and evaluates four ML regression models - Extra Trees, Random Forest, XGBoost, and CatBoost - to predict key antenna parameters such as S₁₁, gain, and bandwidth. Each model's performance is assessed using metrics like Mean Absolute Error (MAE), Mean Squared Error (MSE), R-squared (R2), Mean Absolute Percentage Error (MAPE), and Root Mean Squared Error (RMSE) across different training and testing set configurations (30%, 50%, and 70%). The Extra Trees model achieves the best performance for predicting gain, with an R2 of 0.9990, MAE of 0.0069, MSE of 0.0002, RMSE of 0.0145, and MAPE of 0.3106. Feature importance analysis reveals that specific features, such as pr and p0 for gain and Ya and Xa for bandwidth, are critical in the predictive models. These findings highlight the potential of ML methods to improve the efficiency and accuracy of metamaterial antenna design.

Radon-Fourier transform (RFT) is able to effectively overcome the coupling between the range cell migration (RCM) effect and Doppler modulation by searching along range and velocity dimensions jointly for the moving target, which depends on envelope alignment and Doppler phase compensation. However, without effective clutter suppression, clutter would also be intergraded via RFT. Thus, the adaptive RFT (ARFT) has been proposed to clutter suppression by introducing an optimal filter weight, which is determined from the clutter's covariance matrix as well as the steering vector for the moving target with the consideration of RCM effect. Nevertheless, the ARFT needs to address the difficulty for real implementation, i.e., computational complexity is too high to a large number of pulse samples. It is known that to obtain the inversion the sample covariance matrix (R_cn^-1) is order M³, i.e., O(M³), in which $M$ is the order of the matrix. It is the most complexity consumed step in ARFT. In this paper, we propose a modified adaptive RFT (MARFT) method to obtain R_cn^-1 with recursive computation, which takes the complexity order M², i.e., O(M²). Simulations show that the proposed method has the same clutter suppression results as the conventional ARFT method, where the computational complexity is much lower.

In order to solve the requirements of multi-channel communication applications, this paper proposes a miniaturized dual-passband substrate integrated waveguide filter with asymmetric passband response. The design uses a half-mode substrate integrated waveguide (HMSIW) cavity, which is loaded with a back-to-back complementary open resonant ring (CSRR) according to the vanishing mode propagation theory to generate a passband response lower than the HMSIW basic mode TE101, further reducing the cavity size. In addition, the band-resistive characteristics of the single-ring structure of the CSRR resonator are analyzed, and a C-slot is added at the feeder to improve the out-of-band characteristics of the second passband. Through simulation optimization and testing, the center frequency of the dual-passband filter is 4.05 GHz/8.64 GHz; the relative bandwidth is 16%/44%, the insertion loss of both passbands is better than 0.8 dB; the physical test results are consistent with the simulation ones; and the size of the filter is only 0.42λ_g × 0.14λ_g. It shows that the proposed filter has the characteristics of small size and low loss, and can be widely used in multi-channel RF front-end systems in the field of wireless communication.

Based on dielectric filling, a microstrip grid antenna with six grids is designed in this paper. The broadband characteristics are achieved by increasing the thickness of substrate. An N-type penetrating coaxial port is adopted to feed the antenna for realizing high power capacity. Firstly, the influence of the grid parameters variation on the reflection coefficient was analyzed through the simulation model. Then the structure of the antenna was optimized. Secondly, a prototype of the antenna was fabricated according to the optimized results. The measured results of the fabricated antenna show that the impedance bandwidth of the designed microstrip grid antenna can reach (taking |S₁₁| < -10 dB as the reference) 24.3% ranging from 2.22 GHz to 2.83 GHz. The power capacity of the antenna in the 2.5 GHz can reach 229 Watts according to the measured result of power capacity. Therefore, the designed antenna can be effectively applied in the field of high power irradiation test and high power interference performance test of electronic equipment.

In this paper, a low profile UHF-RFID reader antenna with high front-to-back ratio is presented. The antenna consists of a probe-fed U-slot rectangular patch antenna loaded with a slotted AMC reflector, formed of 2 × 2 unit cells. By incorporating the AMC reflector, a compact profile height of 0.049λ (λ is the wavelength at 910 MHz) is achieved with high gain and front-to-back ratio. The proposed reader antenna is fabricated and measured. The experimental results are similar to those predicted by electromagnetic simulation and validate the proper operation of the antenna across the entire UHF-RFID band (860-960 MHz). Moreover, the realized prototype exhibits a measured realized gain and a front-to-back ratio (F/B) greater than 5 dBi and 24 dB, respectively. The proposed design offers the advantages of low profile, high gain and F/B ratio, rendering it suitable for compact RFID readers.

This paper introduces a new triple-band antenna driven indirectly by a feed line for multiple wireless applications. The structure of this antenna is based on the creation of a set of slots and slits on the ground plane mounted on a substrate with relative permittivity of 4.4 and thickness of 1.6 mm. On the other hand, a 50-ohm microstrip feed line has been fixed. It is found that the proposed antenna offers a triple-band fashion with -10 dB impedance bandwidths suitable for most recent wireless applications. The first band extends from 1.6 GHz to 2.8 GHz, which covers LTE bands (1, 2, 3, 4, 9, 10, 23, 24, 25, 33, 34, 35, 36, 37, 39 and 40), 2.4 GHz-Bluetooth, and 2.45 GHz ISM. The second band extends from 3.38 GHz to 3.6 GHz, which covers most WiMAX applications, while the third band reconciles 5.8 GHz-ITS and 2.4/5.8 GHz-WLAN. A prototype of the proposed antenna has been successfully simulated, fabricated, and measured.

In this paper, three kinds of filters are designed, all of which are based on the basic multi-layer structure of microstrip-slot wire-microstrip wide edge coupling. The ultra-wideband filter is realized by three-class connection. The intermediate coupling layer of coplanar waveguide and multimode resonator is designed to realize the double broadband filter. The ultra-wideband filter is realized by using a curved T SIR structure and changing the middle coupling slot structure. The purpose of this paper is to construct a stable and easy to generalize multilayer filter design method, which can achieve broadband and high selectivity, and can realize dual passbands.

This paper introduces a 12-element asymmetric mirror-coupled loop antenna for integration into 5G smartphones. The proposed antenna includes six identical asymmetrically mirrored (AM)-coupled building blocks, each consisting of two gap-coupled loop antennas, with each building block dimensioning a mere 12×7 mm². The unique architecture of the proposed antenna yields an isolation performance exceeding 14 dB without the necessity for ancillary decoupling elements and effectively covers the dual-band 5G mobile frequency bands of 3.3-3.6 GHz and 4.8-5.0 GHz. The antenna was optimized using simulation software HFSS, and the results indicate an antenna's envelope correlation coefficient of less than 0.016 and an efficiency range of 72%-81%. Finally, the performance of single-hand and double-hand handset smartphone modes is discussed, which still exhibit good radiation and MIMO performance under both modes, demonstrating their stability in practical applications. Simulation and measurement results indicate that the proposed 12-element MIMO antenna holds great promise for 5G smartphone applications.

In a number of wireless communication systems with multibeam antennas, the distance from the antenna to subscribers in different parts of the service area varies significantly. Such systems include high-altitude platform station communication systems, communication systems based on low Earth orbit and medium Earth orbit satellites, and several others. If such a system uses an antenna with identical beams, the throughputs of communication lines in different cells can differ by more than an order of magnitude due to the variation in distance. To equalize throughputs across all cells within the service area, an antenna with different beams can be employed. The gain of these beams should be proportional to the squared slant ranges to the centers of the served cells. The gain of a beam can be modified by altering its size and shape. This paper proposes a method for service area partitioning in communication systems that accounts for the slant range to subscribers. It determines the shapes and profiles of the ideal contoured beams and presents optimized contoured beams for a real antenna.

In the landscape of wireless communication, smart antennas, or adaptive array antennas, have emerged as vital components, offering heightened gains and spectral efficiency in advanced communication systems such as 5G and beyond. However, augmenting network coverage, capacity, and quality of service remains a pressing concern amid advancing communication technologies and escalating user demands. Array antennas with reduced sidelobe levels, high directivity, and increased beam steering capabilities are sought after to address these challenges. This paper explores convex optimization as a potent tool for array synthesis problems, offering robust performance and solution efficiency. By formulating optimization problems as convex programming, sidelobe reduction challenges can be efficiently addressed. The paper presents a comprehensive investigation into convex optimization-based approaches for array pattern nulling, assessing their performance and computational efficiency in various scenarios. Numerical examples demonstrate the efficacy of the proposed methods in maintaining the main lobe, controlling sidelobe levels, and placing nulls at interfering directions, thereby advancing the state-of-the-art in smart antenna technology.

A new dual-polarized compact crossed-notched dielectric resonator antenna (DRA) array with high-gain and wideband performance is proposed for low-band massive multiple-input multiple-output (MIMO) applications at the 700 MHz band of 5G new radio (5G NR) technology. The DRA element consists of three dielectric layers with relatively high relative permittivity constants (ε_r1 = 15 for the bottom and top layers and ε_r2 = 23 for the middle one) for a compact antenna. Characteristic mode analysis (CMA) of a rectangular DRA reveals that two pairs of degenerate modes, namely M2/M3 and M4/M5, resonating at 0.4 and 0.6 GHz respectively can be used to achieve dual polarizations with a proper feeding strategy. By jointly reshaping the conventional DRA along with adding a notch into the middle dielectric layer the two pairs of degenerate modes are merged to produce a broad bandwidth with a compact size of 0.2λ_max × 0.2λ_max (λ_max being the wavelength at low-frequency point). The measured results show an impedance bandwidth of 13.15% (710 MHz-810 MHz) and an isolation of less than -17 dB. Furthermore, the antenna exhibits a good radiation pattern over the working band with a high gain of 7 dB. Finally, the proposed element is tested in a massive MIMO system of 3×4. The results exhibit a wideband of 17.7% and high isolation of more than 12 dB along with a stable gain of 5 dBi within the operating band.

In this paper, a diamond-shaped broadband high-gain microstrip patch antenna based on a folded floor structure is proposed. The overall dimensions of the antenna are 108 mm × 100 mm × 25 mm. Additionally, it contains a radiating microstrip patch, a folded ground plane, and a capacitive feed strip. The broadening of the antenna's operating band is achieved by enhancing the microstrip radiating patch and the capacitive feed band. The original rectangular structure was transformed into a rhombic structure, enabling the radiating patch to absorb the current more effectively and achieve a better impedance match for the antenna operating around 5 GHz. The radiation performance of the antenna is maximized by utilizing the folded floor structure. Measured results show that the impedance bandwidth of the antenna is about 61.5% (2.84 GHz-5.36 GHz), covering 5G dual bands. Meanwhile, the peak gain reaches 12.6 dBi, and the average gain reaches 10.7 dBi.