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.
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.
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