The contrast current density volume integral equation, discretized with piecewise constant spatial basis and test functions and Dirac-delta temporal test functions and the piecewise polynomial temporal basis functions, results in a causal implicit marching-on-in-time scheme that we refer to as the marching-on-in-time contrast current density volume integral equation (MOT-JVIE). The companion matrix stability analysis of the MOT-JVIE solver shows that for a fixed spatial and temporal step size, the stability is independent of the scatterer's dielectric contrast for quadratic spline temporal basis functions. Whereas, Lagrange and cubic spline exhibit instabilities at higher contrast. We relate this stability performance to the expansion and testing procedure in time. We further illustrate the capabilities of the MOT-JVIE based on quadratic spline temporal basis functions by: comparing the MOT-JVIE solution to time-domain results from literature and frequency-domain results from a commercial combined field integral equation solver. Finally, we present a long time sequence for a high-contrast scatterer discretized with 24,000 spatial unknowns.

In this paper, a small antenna is proposed to diagnose skin sarcoma from the embryonic stage to the metastasis stage. The prototype consists of a new antenna structure with a surface of 31.3 x 15.65 mm² and a 35 μm copper sheet engraved on a 1.6 mm FR-4 substrate. The diagnosis is based on the shift in resonance frequency when the antenna is positioned on malignant tissue. For the simulations, a three-layer body Phantom (skin, fat, and muscle) and a half-sphere tumor Phantom were considered. Simulations of antenna performances showed that for a tumor of 26.17 mm³, the resonance frequency decreases by 7.5 MHz. Measurements made on the prototype of the designed antenna show an adequacy between the results of the measurement and those of the simulation.

Coupling system is important for a Wireless Power Transfer (WPT) system, and it directly affects the efficiency and reliability of the WPT system. In some special applications, such as implantable medical devices, the size of the receiving coil of the WPT system is strictly limited. Coupling coils of equal size will not meet the application requirements. When being applied in implantable medical devices, equal-size coupling coils suffer from shortcomings such as poor anti-offset performance and cumbersome design process. In view of the above problems, in this paper we design a coupled coil structure asymmetrically, so that parameters such as the outer diameter and the number of turns of the transmitting and receiving coils are no longer equal. In this paper, we first analyze the effect of tightly wound and loosely wound coils on the WPT system when they are used separately as transmitting coils, and find that the two different types of coils have different characteristics of the magnetic induction intensity distribution. Then we use the genetic algorithm to optimize the transmission coil and design a new asymmetric coupling system. Finally, we experimentally demonstrate that the optimized coupled system is able to maintain the stability of the output current and the transmission efficiency within a certain range in the presence of the offset, which indicates that the coupling system has a certain ability of anti-offset.

In this paper, a new SAR shield design method based on combining graphene-type absorbing cards with metal sheets via a frequency-selective surface resistive card (FSS-R-card) design is proposed. Based on this method, a low-SAR hexa-band antenna for mobile phone applications is designed. The proposed antenna has a simple structure consisting of two radiation strips and a coupling strip for enhancing the high-frequency bandwidth. The antenna covers multiple frequency bands, namely LTE Band 13 (747-787 MHz); DCS 1800 (1710-1880 MHz); PCS 1900 (1850-1990 MHz); WCDMA (1920-2170 MHz); LTE Band 40 (2300-2400 MHz); and Band 41 (2496-2690 MHz). The FSS-R-card combination acts like a PEC in the low-frequency band and like an R-card in the passband. With this approach, we were able to obtain the optimum results in reducing SAR levels and preserving the antenna efficiency in low bands. The prototype antenna was measured by the SAM head model, and measurement results show that the SAR is reduced up to 51% (at 1.9 GHz) by using the FSS-R-card. The SAR level is under 1.6 W/Kg over the whole band with good efficiency preservation at the low bands.

This paper presents a method for using a 120 GHz frequency-modulated continuous wave (FMCW) radar system for communication. The transmitting unit of the FMCW radar partly consists of a phase locked loop (PLL) control. Through modification, the functionality of this structure is extended for data transmission. The two modes of operation, i.e. radar measurement and data transmission, impose different requirements on the design of the PLL, such as the necessary bandwidth. We show how the phase noise and hence the quality of data transmission can be improved by varying the charge pump (CP) current of the PLL. Simulation results and measurements prove the data transmission potential of the presented method for industrial applications in the field of short-range communication.

Electromagnetic metasurface has become the focus of researchers in the field of electromagnetic absorption in recent years because of its thin thickness, simple structure and high absorption rate. With high real and imaginary parts of the permittivity in the microwave frequency regime, water plays a crucial role in absorbing materials. This work demonstrates a water-based translucent metasurface with 5.2 mm, which is fabricated by 3D printing. By changing the conductivity of water, a metasurface with good absorption performance is obtained, which can realize ultra-wideband absorption in 5.85-23.1 GHz and 5.85-14.8 GHz under the oblique incidence of 40˚. The metasurface has the characteristics of thin thickness, wide-band absorption, and translucency.

Three array antennas are analyzed to expand a 3 dB axial ratio bandwidth using the method of moments. First, we design reference and present antennas comprising loop elements with a perturbation segment and quasi-two sources for circular polarization. It is found that the reference and present antennas have an axial ratio bandwidth of 9% and a 3 dB gain drop bandwidth of 31% (35% for the axial ratio bandwidth), respectively. Subsequently, the present antenna is modified using a sequential rotation technique. It is revealed that the modified antenna shows a gain drop bandwidth of 45% (60% for the axial ratio bandwidth). The simulated results are verified with experimental ones.

The role and applications of millimeter wave (mmWave) Reconfigurable Intelligent Surfaces (RIS) have been rapidly increasing by extending the signal coverage with energy and spectrum efficiency. However, the current RIS designs pose challenges like size and angular insensitivity with efficient beamforming functionalities. In this article, we propose a compact and angularly stable RIS unitcell with incident and polarization angle insensitivity in reflection mode. The footprint of the FR4 substrate is 10x10x1.6 mm³ in size. The unitcell structure consists of circular patch inner cuts as a top layer with a full ground. An AlGaAs pin diode is inserted in the middle of the top layer to get the beamforming. The switchable states provide peak resonance at 32.5 GHz (Bandwidth-444 MHz) and 33.6 GHz (Bandwidth-498 MHz) frequencies. Significant gain values of 11.5 and 13.7 dBi are achieved at the operating frequencies. The designed unitcell provides angular stability up to 90˚ oblique incidences and polarization angles. The AlGaAs pin diode is controlled by applying suitable bias levels using Arduino Uno. The numerical simulation results and experimental validation are performed with incident and polarization angles, which are suitable for adapting to the challenges in mmWave applications.

Currently, numerical methods used for the coupling analysis of printed circuit board (PCB) traces excited by ambient wave are still rare. In this work, a time domain hybrid method is presented for the coupling simulation of parallel traces of PCB efficiently, which is consisted of the finite-difference time-domain (FDTD) method, transmission line (TL) equations, and subgridding technique. Within this method, the coupling model of parallel traces on PCB is constructed by using TL equations firstly. Then, the p.u.l (per-unit-length) inductance and capacitance parameters of the traces are calculated by the empirical formulas obtained by the fitting of measurement data in the literature. And the FDTD method combined with the subgridding technique is applied to model the structures of PCB substrate and ground plane to obtain the excitation fields of the traces, which are introduced into TL equations as equivalent source terms. Finally, the central difference scheme of FDTD is utilized to discretize the TL equations to obtain the transient responses on the terminal loads of the traces. The significant features of this presented method are that it can realize the synchronous calculations of electromagnetic field radiation and transient responses on the traces, and avoid modeling the fine structures of the traces directly. The accuracy and efficiency of this presented method have been verified via the numerical simulations of multiple parallel traces on PCB in free space and inside a shielded cavity by comparing with the Baum-Liu-Tesche (BLT) equation and electromagnetic software CST.

This paper addresses the challenge of improving the digitalisation of 5G communications, with multiple-input-multiple-output (MIMO) non-orthogonal multiple access (NOMA) systems employing relaying, by using simultaneous wireless information and power transfer (SWIPT). In the case of a massive number of users, the connections demand a more efficient network. Therefore, we design a novel framework for a relay-assisted SWIPT NOMA system, to analyze the improvement of SWIPT transmission with NOMA. We derive a closed-form expression for a lower range of spectral efficiencies, assess the performance of the designed system through sum rate analysis, and discuss the power splitting ratio dependence of the performance. Finally, the sum rate is calculated to present the capability of this novel scheme.

This paper introduces the new design of a choke loaded horn antenna, at 89.75 GHz for metrology of the large paneled reflector antenna using the Fresnel field based radio holography technique. The proposed choke loaded horn antenna offers the φ cut wise extremely stable phase center (< 2 µm) which is required to obtain < 5 µm surface accuracy during holographic measurement. The design of choke loaded horn antenna has been presented along with its simulation performance and tolerance analysis. The antenna has been developed using a simple computer numerical control (CNC) milling process and characterized in the anechoic chamber. The measured and simulated results are also compared, and a good match has been achieved between the measured and simulated performances of the horn antenna.

To address the stressful and time-consuming problem with the current notched antenna modelling optimization tools, an improved deep multilayer perceptron (DMLP) neural network framework is designed. The method introduces an attention mechanism (Attn) layer to improve the interpretability of the model, uses the leaky ReLU activation function to prevent the gradient from vanishing, and optimizes the structure of the DMLP model using an improved particle swarm algorithm (PSO) to improve the model prediction accuracy. Then, the notch structure geometric parameters of the designed double-notch ultra-wideband (UWB) antenna serve as input to predict the return loss S₁₁ of the antenna. The experimental results show that the method reduces the root mean square error of prediction for S₁₁ by 73.01% compared to the traditional MLP and 64.14% compared to the unimproved DMLP, which provides a solution for modelling notched UWB antennas and helps to optimize the design of this type of antenna.

This paper presents a compact electrically tunable bandpass filter with continuous control of center frequency and bandwidth independently. The filter consists of two coaxial dielectric resonators loaded with two varactors for center frequency tuning. A symmetrical Y-type capacitor network used for tuning bandwidth is proposed. A prototype made of dielectric ceramics with dielectric constant of 88 has been designed, fabricated and measured. The center frequency varies from 0.562 GHz to 0.845 GHz and 3 dB bandwidth is tuned from 117 MHz to 194 MHz at the center frequency of 845 MHz. A constant absolute bandwidth of 141 MHz is realized by varying simultaneously bias voltages. The volume of fabricated filter containing bias networks is 24×22×6.5 mm³ (0.045λ₀×0.041λ₀×0.012λ₀). The measured results agree with the simulation outcome.

In this paper, a freely extendable dual-band multiple-input multiple-output (MIMO) antenna for 5G wireless communication is proposed. The highlight of the antenna is that the 2-port array can be freely extended by repeating the radiating elements and decoupling structure periodically. A 2-port MIMO antenna is proposed firstly. It consists of two dual-band radiating elements placed side by side with edge-to-edge spacing of 0.08λ₀. Then, a novel multiple bent split ring (MBSR) metamaterial (MTM) unit is designed. By adjusting the size, two kinds of units with single negative characteristics at two resonance points are obtained. By arranging the MBSR-MTM units cleverly between the two elements, dual-frequency decoupling is realized. Simulated and experimental results indicate that the antenna can operate at frequencies of 2.57~2.62 GHz and 3.5~3.6 GHz with the highest isolation of 30.2 dB and 44.5 dB, respectively. Additionally, the envelope correlation coefficient (ECC) is much smaller than 0.05, implying good diversity performance. Furthermore, simulated and experimental results show that the 2-port antenna can be freely extended to multiple-port MIMO antenna without any modification, and the isolation between different ports remains high. The antenna has a compact structure, low profile, and high isolation, providing an excellent choice for 5G wireless communication.

This paper focuses on the decomposition of different modes of Loran-C resultant waves, including ground waves and one-hop/two-hop sky waves, propagating in the Earth-ionosphere waveguide obtained from direct finite-difference time-domain (FDTD) modeling in the presence of the natural magnetic field. After providing the FDTD iterative formulas for the ionosphere affected by the natural magnetic field, the Loran-C resultant waves propagating in the anisotropic Earth-ionosphere waveguide are estimated using the FDTD algorithm. In both the daytime and nighttime ionosphere models, different orientations of the natural magnetic field are taken into account. The arrival times of the different propagation modes for the resultant waves were then determined using a multipath time-delay estimation method. With the above delays, the amplitudes of the different modes are acquired by solving overdetermined equations. Finally, the decomposition results are compared with those obtained in the absence of the natural magnetic field. The numerical experimental results indicate that, with a radiation power of 1 kW and a natural magnetic field of 0.5 Gs, the influence of the direction of the natural magnetic field on the field strength of one-hop sky waves is significant when the propagation distance of LF radio waves is less than 1000 km. Radio waves have multipath effects such as convergence, divergence, and diffraction due to the curvature of the Earth and the ionosphere. This results in significant interference phenomena when the propagation distance of two-hop sky waves is greater than 500 km.

A model prediction based leading angle flux weakening control method is proposed to improve the dynamic and steady-state performance of permanent magnet synchronous motors during the flux weakening process. First, the mathematical model of a permanent magnet synchronous motor is used to construct the prediction model in this method, and then a thorough analysis of the permanent magnet synchronous motor's flux weakening control procedure is carried out. Secondly, based on the principle of model predictive control and the existing delay problems, the corresponding delay compensation method is proposed, and the leading angle flux weakening control method is applied to the proposed model predictive control algorithm, so as to achieve flux weakening speed-up control. Finally, the prototype is used to confirm the effectiveness and precision of the proposed technique. The experimental results show that the leading angle flux weakening control method based on model prediction has faster dynamic response to speed and current than the traditional vector flux weakening control method. At the same time, the steady-state current amplitude is smaller, which has superior current control.

Aiming at the problem of slow response speed and poor anti-interference ability using the traditional PI control in the direct torque control strategy of brushless DC motor (BLDCM), the direct torque control (DTC) of the BLDCM based on the sliding mode change (SMC) structure is proposed. In the BLDCM DTC system under the new flux linkage set mode, the traditional PI control is replaced by the improved SMC control to realize the new torque given mode and realize the DTC of the BLDCM. Firstly, the integral sliding mode surface is used instead of the traditional linear sliding mode surface to optimize the continuity of the SMC structure and reduce the high-frequency perturbation caused by the differential phase, thus reducing the smooth torque and system steady-state error. Secondly, the system is simulated by MATLAB/SIMULINK; the given torque of the improved SMC is the most stable; and the speed response curve is smoother. Finally, the construction of the BLDCM test platform is completed. The experimental results show that in the BLDCM DTC control system of the new flux linkage set mode, based on the improved SMC, the system has faster response speed and stronger anti-interference, and shows stronger dynamic and static performance.

Solid dielectric horn antennas have a directional radiation pattern and high gain. However, even when a solid dielectric horn antenna is excited with the fundamental mode metallic waveguide, there is a possibility that higher order modes in the guided region will be generated. Also, the energy can leak from the normal direction to the dielectric horn generating a leaky mode. It is one of the reasons that higher-order guided modes and leaky modes analysis of horn becomes important. In this paper, propagation characteristics for solid dielectric horns are derived and computed for fundamental and higher-order guided and also leaky modes in a solid dielectric horn antenna. We have also analyzed the radiation characteristics of the leaky mode and guided mode of a solid dielectric horn. Finally, radiation equations for a solid dielectric horn antenna that were deduced earlier by some of the authors, but omitted for brevity are given and compared with numerical and measured results. These results have been further verified by comparing them with the already reported literature on guided mode radiation characteristics of the solid dielectric horn. From the plotted graphs given in the paper, we can infer that the proposed propagation constant equations and radiation equations predict dispersion characteristics and the radiation pattern of guided and leaky modes well, respectively.

This article presents a novel numerical approach to reduce scattering echoes in the front region of dielectric objects with the method of auxiliary sources. The method involves using a Gaussian radio pulse covering the 6-12 GHz frequency range. The approach involves optimizing the dimensions and dielectric permittivity of an elliptical cylinder in order to make it invisible, thus eliminating the need for metamaterial cloaking. The proposed approach has been validated by comparing the results of numerical experiments obtained during pulse echo observations with the FDTD and MoM numerical methods. The proposed method is a highly efficient and practical approach for scattering problems, such as scattering echo reduction, offering comparable results to FDTD and MoM methods with significantly reduced computational requirements.

The purpose of this paper is to study the RF/microwave constant phase shift (CPS) designed as an integrated circuit (IC) in 130-nm Bi-CMOS technology. The CPS understudy is constituted by a bandpass (BP) negative group delay (NGD) passive cell combined in cascade with a positive group delay (PGD) circuit. The CPS real circuit is represented by a CLC-network associated in cascade with a BP-NGD passive cell. The CPS characterization is based on the S-parameter modelling. The CPS is analytically modeled by the frequency independent transmission phase modelling by the mathematical relation φ(f)=a*exp(-j*φ₀) = constant around working frequency [f_n-Δf/2, f_n+Δf/2] by denoting center frequency f_n and frequency band Δf. The analytical principle of the constant PS is explored by means of the RLC-network based NGD cell. The design formula of the NGD and CLC passive circuit parameters in function of desired operation frequency is established. The validity of the developed theory is verified with a proof-of-concept (POC). A CPS miniature IC having physical size 1.15 mm × 0.7 mm is designed and implemented as POC in 130-nm Bi-CMOS technology. The ADS® and layout versus schematic of Cadence® simulation results from 130-nm Bi-CMOS CPS POC confirms the theoretical investigation feasibility. The simulated results of the obtained CPS IC POC layout show φ₀=-67°+/-1° phase shift around f_n=0.85 GHz within the frequency band delimited by f₁=0.73 GHz to f₂=0.984 GHz or Δf=f₂-f₁=254 GHz. The CPS robustness designed in 130-nm Bi-CMOS IC technology is stated by Monte Carlo statistical analysis from 1000 trials with respect to the component geometrical parameters. It was reported that the phase shift and insertion loss flatness's of the CPS IC is guaranteed lower than 5% in Δf/f_n=30% relative frequency band around f_n.