In this article we present a ring Dielectric Resonator Antenna (DRA) fabricated on three-dimensional (3D) printed Acrylonitrile Butadiene Styrene (ABS) filament. The 3D printer offers antenna easy to fabricate and the possibility to design new antennas shapes more complex. The simulation performed using CST software 2020 shows that the proposed ring DRA has two resonance frequencies 23.5 GHz and 26.4 GHz with an obtained great gain 9.5 dB and 10.5 dB, respectively. A wideband about 42.4% was measured.

A combinatorial quantitative reconstruction method employing Subspace-based Virtual Born Iteration Method (SVBIM) along with a greedy compressive sensing algorithm, Sparse Reconstruction by Separable Approximation (SpaRSA) to solve the ill-posed inverse problem in microwave imaging is proposed in this paper. SVBIM makes use of the contribution of the variational induced current to arrive at a better estimate of the permittivity profile in each iteration. SpaRSA operates in the sparse domain and reduces the computational overload, thereby guiding the inverse problem towards a faster global optimum solution. The merger of these two algorithms helps to reconstruct breast profiles having high-permittivity tumour inclusions (ε = 60) with reduced error. The proposed reconstruction method is capable of extracting the salient information regarding tissue differentiation (permittivity and conductivity) and dielectric distribution of various tumour and fibroglandular inclusions within the object, dimensions, resolution, size, shape and coordinate localization of inclusions. In comparison to various methods reported in literature, the results obtained using the proposed method are highly encouraging. In the presence of 30 dB noise, the above-said imaging technique produces a significantly reduced permittivity error value of 0.47 in the reconstruction of tumour inclusions as against 0.85 and 0.71 in the case of TV norm and Re-weighted Basis Pursuit methods respectively. The experimental validation is carried out using a phantom having three inclusions of sizes 10 mm, 6 mm, and 3 mm. The inclusions have been localized successfully with errors of 0.089, 0.133, and 0.21, respectively.

A novel balanced-to-unbalanced (BTU) all-port reflectionless filtering power divider without loading additional absorptive branches at input and output ports is proposed in this paper. The proposed power divider includes two reflectionless filtering networks, four transmission lines, a phase inverter, and two isolation resistors. Unlike the existing filtering power dividers that require additional absorptive branches to be loaded at each port to achieve reflectionlessness at all ports, the proposed power divider achieves all-port reflectionlessness by embedding only two reflectionless filtering networks in the BTU power dividing circuit. Meanwhile, this reflectionless filtering network also introduces two transmission zeros located at the lower and upper sides of the passband, respectively, for high selectivity. To validate the proposed power divider topology, a 2.0-GHz BTU filtering power divider is designed and fabricated with a 3-dB filtering bandwidth of 40.1%. The 10-dB reflectionless bandwidth for the balanced port is 98.7% from 0.940 to 2.772 GHz and that for the unbalanced ports covers the entire measurement frequency from 0.5 to 3.5 GHz, achieving good all-port reflectionless characteristics.

In this paper, a low cross-polarization level, low radar cross section (RCS), conformal, ultrawideband, polarization-insensitive absorber utilizing sinusoidal periphery annular ring (SPAR) resonator based novel resistive metasurface is presented. The proposed absorber operates with more than 90% absorptivity over the frequency range 7.68 GHz-24.90 GHz encompassing X-, Ku- and major portion of K-bands. The absorber consists of two sinusoidal peripheries annular rings embedded with lumped resistors, placed on top of a 0.1 mm thin low cost FR-4 substrate which is supported by metal backed foam. The sinusoidal periphery on the annular rings improves the absorption bandwidth and miniaturizes the proposed structure. Cross-polarized reflected component from the absorber is also investigated and included in the estimation of absorptivity to validate that the proposed structure functions as an absorber and not as a reflective type polarization converter. An equivalent circuit analysis based on the transmission line model is also presented. Novelty of the proposed article's lies in the design approach for the proposed absorber in which flexibility is incorporated to choose unit cell geometrical parameters as per the limiting frequencies (upper and lower) of desired band along with some miniaturization aspects of the absorbing structure. Furthermore, 10 dB RCS reduction is discussed, and the formula is derived by including cross-polarized reflection component of the incident wave in estimation. The proposed absorber is validated through theoretical, simulation, and experimental studies for planar and conformal applications.

The separation of water droplets on the insulator umbrella surface is an important factor that increases the probability of flashover along the surface. Previous studies have only investigated the motion and deformation of water droplets on the horizontal insulator sample surface and their effect on flashover voltage. In actual composite insulators, the umbrella skirt surface is usually inclined at a certain angle. The influence of the umbrella angle on the motion law and flashover voltage of water droplets has not been fully studied in recent research. In this paper, focusing on the separated water droplet on insulator sample surfaces with different inclination angles, the motion modes and flashover characteristics of the water droplet are studied by using multi-physics finite element simulation and AC flashover experiment. The results show that the motion modes of water droplets changes with the inclination angle of the umbrella surface. The water droplet oscillates left and right under the AC electric field when the inclination angle is small. As the inclination angle increases, the oscillating trend of the water droplet weakens. When the inclination angle is large enough, the deformation of the water droplet shows two forms: sliding and stretching. As the inclination angle of the umbrella surface increases, the flashover voltage decreases, and the decreasing trend of the flashover voltage is greater when the inclination angle is larger.

This paper presents a small size M-shaped polygonal slot antenna for X-band satellite telemetry and Synthetic Aperture Radar (SAR) applications. The proposed antenna has been designed on a Roger RT-Duroid 5880 substrate. The reflection coefficient |S₁₁| of the proposed antenna covers the whole X-band from 6.63 GHz to 12.566 GHz. The proposed antenna is circularly polarized with axial ratio (AR) bandwidth that extends from 7.76 GHz to 8.58 GHz. The proposed antenna provides a simultaneous dual circular polarizations (RHCP and LHCP). The gain of the proposed antenna varies between 6.6 dBi and 9.4 dBi. The proposed antenna realizes an efficiency of 92%. The overall size of the proposed antenna is 17 x 16 x 0.508 mm³ (0.56λ₀ x 0.53λ₀ x 0.016λ₀). Therefore, it is suitable to be employed in satellite telemetry application from 7.9 GHz to 8.4 GHz especially for CubeSats that have limited surface area. Apart from that, this antenna finds its applications in SAR on small satellites from 9 GHz to 10 GHz, military, and RFID tag (tracking-equipment). It has been observed that the measurement results match the simulated ones. The proposed antenna design can be practically employed for the previously mentioned applications.

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.