A high port isolation dual-polarized microstrip patch antenna based on artificial magnetic conductor (AMC) surface is proposed in this paper. The antenna is composed of two stacked patches and H-shaped coupled slots with improved impedance matching bandwidth. The feed network is composed of two orthogonal microstrip feed lines for dual polarizations, and metallic vias are arranged around them to improve the port isolation. The AMC surface is designed and loaded below the feed lines. The electric field coupling between the feeding slots on the ground are reduced, and the port isolation is greatly improved. The simulated results show that the proposed antenna has a port isolation better than 48 dB and a cross-polarization level of -26 dB over the frequency of 9.3-9.5 GHz. Moreover, based on zero-reflection phase characteristic of the AMC, the profile of the antenna is reduced to 7.3 mm (0.23λ₀，λ₀ is the wavelength at 9.4 GHz). A prototype is fabricated to verify the analysis of proposed antenna. The measured results indicate that a high port isolation better than 44 dB and a cross-polarization level lower than -22 dB are achieved. The maximum gain is higher than 6.98 dBi and 6.5 dBi for the vertical and horizontal polarizations, respectively. With the advantages of high port isolation and low profile, this antenna offers a good candidate for weather radar applications.

The article focuses on the problem of determining optical semiconductor cell characteristics that can be used for plasma antenna development. The problem outlined is associated with the insufficient characteristics (for example, electrical conductivity) in datasheets for semiconductors on the market, which are for the simulation of antennas. An optical semiconductor conductivity calculation method, when representing it as a segment of a microstrip transmission line (a coplanar waveguide) with a known transmission coefficient (S21) as a radio frequency signal passes through it, is suggested. The article presents a simple and easy-to-use experimental setup for the trial of the suggested method. The essence of the method lies in using a PCB with a microstrip line with a gap in the middle. SMA ports for connection with a vector network analyzer are on the edges. A studied optical semi-conductor cell is placed at the transmission line gap, and the transmission coefficient between the two ports can be measured. In addition to that, the conductivity of the cell under illumination can be calculated based on the proposed formulas. The article presents the results of measuring some optical semiconductor cells (resistors, diodes, transistors) and their conductivity calcula-tions under illumination. The results obtained on the conductivity of photocells can be used for simulating antennas that involve optical semiconductor cells.

This paper proposes a bilayer segmented asymmetric V-type magnetic structure of interior permanent magnet motor to address the problems of large air-gap magnetic density zero region, high air-gap magnetic density distortion rate, and large output torque ripple in the traditional V-type permanent magnet synchronous motor. Firstly, the superiority of the bilayer segmented asymmetric V-type structure is verified using finite element simulation compared with the bilayer conventional V-type and bilayer segmented symmetric V-type structures. Secondly the analytical model of the air-gap magnetic density, output torque, and torque ripple is established. Then, with the optimization objectives of reducing the air-gap magnetic density distortion rate, increasing the output torque, and reducing the torque ripple, and with pole-span angles of the bilayer segmented asymmetric V-type structure as the optimization variables, each optimization variable is subjected to weighted sensitivity stratification. The response surface optimization is applied to the low and medium-level sensitivity optimization variables, while a Pareto frontier distribution is used to obtain the set of the effective values of the high-level sensitivity optimization variables. The optional combination of the pole-span angles of the segmented asymmetric V-type structure is objectively selected by applying the TOPSIS method. Finally, the effectiveness of the optimized design is verified by finite element simulation and prototype tests. The results show that the bilayer segmented asymmetric V-type structure can reduce the percentage of the zero region of the air-gap from 4.82% to 3.91%, which is reduced by 18.8% and lower the air-gap magnetic density distortion rate from 0.263 to 0.226, which is reduced by 14.1% while ensuring good output characteristics with improving the average output torque from 14.842 N.m to 16.418 N.m, which is increased by 10.6%, and reducing the torque ripple from 0.169 to 0.156, which is reduced by 7.7%.

Wireless communication has revolutionized modern connectivity, with millimeter-wave (mm-Wave) technology emerging as a key component of next-generation networks due to its ability to deliver fast data rates and large capacity. Hybrid precoding is an important approach in mm-Wave MIMO systems for optimizing spectral efficiency, and it relies largely on accurate channel state information (CSI). The sparse characteristic of mm-Wave channels allows compressive sensing (CS) methods to be used for efficient channel estimation, considerably lowering pilot overhead and computational complexity. This study describes a novel hybrid precoding technique designed for reliable multi-user situations. The proposed two-stage framework uses SVD-based equal-gain transmission (EGT) for analog precoding and a Kalman filter for baseband precoding to effectively reduce inter-user interference. Numerical assessments show that the EGT-Kalman precoding method is comparable with standard strategies like zero-forcing (ZF) and MMSE precoding in terms of spectral efficiency. Furthermore, the pilot overhead is calculated, indicating the efficiency of the suggested technique in reducing training requirements while maintaining performance. This study highlights the promise of adaptive precoding techniques in developing mm-Wave communication systems by providing resilient performance in stable multi-user scenarios while tackling the challenges of sparse channel estimation.

To effectively receive circularly polarized (CP) waves at large angles, it is necessary for antennas to have large axial ratio beamwidth (ARBW). For instance, geostationary satellite receiver antennas employed in regions with high latitudes necessitate a broad ARBW. In this paper, the mechanism to broaden ARBW is analyzed, and a CP antenna with low profile is designed and fabricated. With L-shaped branches and vertical extension segments (VESs), ARBW of the proposed antenna has been effectively broadened. Moreover, compared with recently reported wide ARBW artworks, it features a simple structure and feeding mechanism. The proposed antenna within the working bandwidth (from 4.79 to 4.95 GHz, 3.3%) achieves a 3 dB ARBW of 243° in the φ= 0° plane while the 3 dB ARBW reaches 199° in the φ= 90° plane. The measured results agree well with the simulated ones.

In this paper, an enhanced FDTD algorithm is proposed for efficient characterization of HTS (high temperature superconductors) microwave planar filters. The developed algorithm, which can be generalized to any microwave planar circuit, is based on the two-fluid phenomenological model. Further, an irregular mesh discretization allowed improving the CPU time. Also, the thermal effects and the normal conductivity have been rigorously taken into account for better performance. The impact of the operating temperature as well as the choice of the superconductor thickness was investigated. Computed results are in good agreement with simulated data using commercial software.

The Double Stator Magnetic Field Modulation Motor (DSMFMM) realizes the magnetic field modulation effect and optimizes the torque ripple effect by accurately optimizing the flux line. In order to further explore the influence of permanent magnets (PMs) magnetization model on the performance of DSMFMM, this paper conducts a comparative study on the performance of three motors with radial magnetization, Halbach magnetization, and Spoke magnetization. Firstly, three motor models are designed based on the same outer radius and axial length, and the flux lines of the three motors are analyzed in detail. Secondly, the static and dynamic performances of the three models are compared by finite element analysis (FEA) method. Compared with the conventional radial magnetization structure, the DSMFMM structure with Halbach magnetization and Spoke magnetization improves the output torque and torque density of the motor.

This study proposes a dual-band microwave sensor based on a split-ring resonator (SRR) coupled with a pair of L-shaped structures. The proposed sensor has dual functionalities, including the detection of liquid permittivity and solid displacement. An ethanol-water mixture is selected as a sample to measure the permittivity of the liquid. Moreover, FR4 is chosen as the test sample to measure the displacement of the solid. As a result, the maximum frequency detection resolution (FDR) is 1.64, and the average FDR is 1.40. The maximum and average normalized sensitivity (NS) values are 0.073% and 0.06%, respectively. The maximum displacement sensitivity is 10.0 MHz/mm for f_DS2 and 10.5 MHz/mm for f_DS1, while the average displacement sensitivity values are 4.98 MHz/mm and 8.02 MHz/mm for f_DS2 and f_DS1, respectively. These values confirm the sensor's reliable performance and sensitivity across different measurements. In general, the proposed sensor offers several advantages: 1) it operates independently by isolating the electric fields generated by each sensor; 2) it demonstrates dual functionalities, including the detection of liquid permittivity and solid displacement; and 3) it is capable of handling both liquid and solid samples.

This paper introduces a decoupled dual-element array antenna designed to address the challenges of mutual coupling between elements. To tackle this issue, a neutralization line is strategically incorporated to suppress leaky surface currents, while ensuring the antenna's central frequency and radiation pattern remain intact. The dimensions of the neutralization line are carefully optimized using the Whale Optimization Algorithm (WOA) to achieve the best possible performance, focusing on minimizing mutual coupling and enhancing gain. By placing the neutralization line nearby between the two elements, surface currents are efficiently redirected back to the radiating element, preventing leakage to neighboring elements. This approach also results in a more compact structure. The proposed antenna, with overall dimensions of 50 mm x 30 mm x 1.6 mm, is simulated using analytic software. It achieves an impressive 27 dB reduction in mutual coupling and delivers an ultra-wide bandwidth of 1.2 GHz within the ISM band at an operating frequency of 2.4 GHz, with a measured maximum gain of -5 dB. The structure was fabricated, and experimental results closely matched the simulations, confirming the design's effectiveness. By leveraging the WOA optimization method, the geometry of the neutralization line was fine-tuned to maximize performance, significantly improving inter-element decoupling. This design approach is simple yet effective and can be readily extended to other antenna array configurations, demonstrating strong potential for compact and efficient Industrial Scientific and Medical (ISM) band applications.

Millimeter wave synthetic aperture interferometric radiometer (SAIR) can achieve high-resolution imaging without a large physical aperture antenna and has strong application advantages in the fields of earth remote sensing, astronomical observation, and meteorological monitoring. In order to adapt to various payload platforms and detection needs, the existing SAIR array structures are diverse, but the existing imaging methods are difficult to effectively deal with various arrays and achieve stable high-precision imaging inversion. Thus, this paper proposes a general multi-channel fusion imaging network to achieve SAIR imaging inversion of any array structure. First, with the help of the sensor matrix deduction subnet, a high-precision imaging sensor matrix is deduced according to the position of each array element of the SAIR system, and then high-precision image reconstruction is achieved with the help of the multi-channel fusion imaging subnet. The simulation results show that the network has good adaptability and can achieve high-precision imaging inversion of different SAIR array structures.

Neural networks have become a focal point for their ability to effectively capture the complex nonlinear characteristics of power amplifiers (PAs) and facilitate the design of digital predistortion (DPD) circuits. This is accomplished through the utilization of nonlinear activation functions (AFs) that are the cornerstone in a neural network architecture. In this paper, we delve into the influence of eight carefully selected AFs on the performance of the neural network–based DPD. We particularly explore their interaction with both the depth and width of the neural network. In addition, we provide an extensive performance analysis using two crucial metrics: the normalized mean square error (NMSE) and the adjacent channel power ratio (ACPR). Our findings highlight the superiority of the exponential linear unit activation function (ELU AF), particularly within deep neural network (DNN) frameworks, among the AFs under consideration.

The miniaturization of implantable antenna is one of the significant requirements, especially for those devices implanted under the skin, as it reduces prominent appearance and invasiveness. In this paper, we design, simulate, and implement a spiral resonator-based microstrip antenna utilizing the ISM band (2.4-2.48 GHz). A small size, light weight, and flat type are required for under-skin implantation. The proposed antenna dimensions were optimized for a miniaturized volume of (3 × 2.5 × 0.12) mm³, representing the smallest size for under-skin biomedical applications. This miniaturization is achieved using a spiral-shaped radiator and creating slots in the ground layer. In-vivo measurement parameters, including reflection coefficient, are measured on the suggested antenna, showing a gain of -19.9 dBi and a bandwidth of 90 MHz. Specific Absorption Rate (SAR) is evaluated at 316 W/kg, confirming that the proposed antenna meets the necessary human-use safety criteria.

This article presents a dual-band switchable and tunable band-pass filter for Bluetooth and 5G NR applications. The filter functions at 2.41 GHz for Bluetooth and 3.55 GHz for 5G, utilizing independent switching and tuning methods facilitated by PIN and varactor diodes. The suggested design exhibits compact dimensions of 0.177λ_g x 0.096λ_g, a minimal insertion loss of 0.35 dB, and a substantial return loss of 30 dB. Advanced design methodologies, including defective ground structures (DGS) and eigenmode analysis, were utilized to attain precise selectivity and exceptional out-of-band rejection. The engineered filter demonstrates superior performance, with outcomes closely aligning with models, and guarantees little interference with suppression up to 10 GHz. The tuning mechanism provides versatility by independently modifying the operating frequencies of the second band, rendering the design very flexible for dynamic wireless communication settings. This study emphasizes a robust and effective answer for contemporary mobile communication systems.

In this paper, a novel wideband reflectionless filtering patch antenna is proposed. The antenna consists of a filtering patch and an absorption network. The filtering patch includes an E-shaped radiator and two T-shaped radiators. The E-shaped radiator introduces a radiation null, which greatly improves lower-band edge selectivity. The T-shaped radiators introduce an additional radiation null, effectively increasing the filtering performance in the upper stopband. For the absorption network, a quarter-wavelength coupled-line section with two 200-ohm resistors and four short-circuited three-quarter-wavelength transmission lines are used to achieve reflectionless characteristics. To demonstrate the design, an antenna prototype with a center frequency of 3.5 GHz is fabricated and measured. Measurement results manifest that the input reflectionless bandwidth is 63.5% from 2.56 to 4.94 GHz with an antenna gain of 5.8 dBi. At 3.02 and 3.91 GHz, two radiation nulls are also obtained. The lower and upper stopband suppression levels are 18.1 and 14.5 dB, respectively.

The paper introduces a corrugated antenna structure suitable for 5G WLAN application and operates at a frequency of 5.52 GHz. Further, a periodic structure made up of square unit cells is combined with the antenna design, and improvement in gain and impedance bandwidth is observed. The antenna gain without periodic structure is 3.48 dB whereas with periodic structure it is noted as 4.09 dB. The antenna dimensions are 16 mm × 16 mm × 3 mm. Also, the measured bandwidth of the antenna structure without periodic structure is observed to be 210 MHz, and that with periodic structure is 310 MHz.

This paper investigates the low-frequency excitation of a non-magnetic stratified conducting sphere by external sources, using a classical quasi-static approach. We focus on point-impressed sources represented by charges or electric dipoles, which predominantly generate electric fields. The findings have implications for low-frequency scattering theory and can potentially support the assessment of localized human exposure to low-frequency electric fields, such as those from Wireless Power Transfer using capacitive coupling technology. For a sphere with an arbitrary number of homogeneous layers, we develop a numerical-analytical solution inspired by the Exact Difference Scheme. This approach yields a tridiagonal discretized representation of the continuous problem, ensuring uniqueness and computational stability, and allowing for efficient solution via the Thomas algorithm. For a sphere with general radial inhomogeneity, we apply the Finite Difference method. Computational experiments show a strong agreement between these two approaches. We also examine the physical aspects of electric field interaction with a four-layer model of the human head, using the concept of coupling coefficients for the electric field and the generated heat. Our results show that these coupling coefficients increase with the separation between the point sources and the sphere, converging in certain cases to those for a uniform incident electric field. A comparison with the relevant ICNIRP reference levels for the incident electric field is also provided. The comprehensive Wolfram Mathematica code, consisting of multiple modules and including theoretical definitions and explanations of the computed quantities, is available as a supplement to the paper.

A compact spiral cavity backed substrate integrated waveguide (SIW) multiple input multiple output (MIMO) antenna is presented in this paper. The edge-shaped spiral on top of the SIW cavity acts as a dipole antenna. The dual spiral arms are excited from their symmetrical connecting center. The single antenna element in MIMO is rotated such that unit cells are orthogonal to each other forming a compact 2 × 2 and 4 × 4 MIMO SIW antenna. The proposed design shows a wide bandwidth of 930 MHz (13.74 GHz to 14.67 GHz) and 67.68% impedance bandwidth. The overall size of proposed MIMO SIW antenna is 0.9λ_o × 0.9λ_o × 0.024λ_o, where λ_o is the operating wavelength. A return loss of 18.4 dB at 14.17 GHz is achieved. The series of metal pins (in plus shape) at the center of 4 × 4 MIMO improves the isolation to 19.6 dB at resonant frequency. A pattern diversity in broadside direction is achieved by the top spiral arms and its complementary spiral arms at the bottom. The beamwidth of the proposed antenna is 90˚ varying from -45 deg to +45 deg, useful for reliable signal transmission and reception. Thus, the proposed antenna is a symmetrical compact design working at Ku band suitable for radio telescope application.

This study proposes designing and developing a metamaterial absorber that improves the efficiency of solar cells. The design includes circular forms with rectangle gaps etched on the upper surface of an FR-4 substrate, with a copper sheet serving as an isolating substrate for the ground beneath. The structure operates in the tera frequency ranges to accommodate all infrared wavelengths of the sun's spectrum. Furthermore, the constructed metamaterial unit cell is used to build a metamaterial array absorber, which increases the rate of energy harvest from the sun spectrum. The two designs showed absorption rates of approximately 96.75% and 99.85% at 94.85 THz and 109.08 THz resonant frequencies respectively. In addition, a top surface of microwave cross-polarization conversion (CPC) is also generated and simulated. The structure of the proposed microwave unit cell consists of the same metamaterial absorber design. Efficient cross-conversion is achieved across a wide frequency band (9 GHz to 15 GHz), with polarization conversion effectiveness exceeding 99%. The suggested CPC design has three resonance bands with 50% fractional bandwidth (FBW) and achieves a stable polarization response at oblique incidence angles up to 35˚.

This paper proposes a CPW-fed wideband slot antenna with a modified Minkowski fractal island geometry. The antenna comprises a CPW-fed monopole placed within a modified Minkowski fractal island slot. The resonance introduced by the fractal slot combines with the monopole's resonance, resulting in an expanded operational frequency range. The interaction between the monopole and the fractal slot significantly broadens the bandwidth. Return loss measurements confirm a wide bandwidth extending from 2.27 GHz to 7.91 GHz, achieving a fractional bandwidth of 111% covering WLAN, WiMAX, Wi-Fi, and 5G sub-6 GHz bands.

A prototype filter design exhibiting Negative Group Delay (NGD) is presented, based on the ratio of two low-pass classical Bessel filter transfer functions of the same order, but with different 3dB-bandwidths. The resulting design is a reciprocal-Bessel filter transfer function, capped at a finite out-of-band gain. The proposed capped reciprocal-Bessel design is based on a similar concept applied to previously reported capped reciprocal-Butterworth and reciprocal-Chebyshev NGD designs, which use ratios of corresponding classical low-pass filter transfer functions. It is shown that within the in-band frequency range, the synthesized NGD transfer function exhibits a maximally flat group delay characteristic (Bessel-like property). Due to its near-flat in-band group delay characteristic, the design is suitable for constant phase shifter applications. For high design orders, it is shown that the achieved NGD-bandwidth product has an upper asymptotic limit, given by the square root of the out-of-band gain in decibels. When the prototype baseband transfer function is translated to a non-zero center frequency, it is demonstrated that resonator-based implementations are feasible via Sallen-Key, as well as all-passive ladder topologies. A combined in-band magnitude/phase distortion metric is evaluated for selected design examples and applied Gaussian and sinc input waveforms, and it is shown to be proportional to the design order and out-of-band gain. The proposed design's distortion metric is also shown to be generally lower than the previously reported capped reciprocal-Butterworth and reciprocal-Chebyshev designs.