Thin-wire finite-difference time-domain model for insulated and resistively loaded cylindrical antennas driven by coaxial lines

A thin wire-based finite-difference time-domain (FDTD) model for a simple analysis of insulated and resistively loaded cylindrical antennas fed by coaxial lines is proposed. The resistive loading and the coaxial feed line are approximated to equivalent resistors along the antenna axis and the equivalent source over the infinitesimal feed gap, respectively. The effects of the insulation are corrected by employing thin-wire approximation and the boundary condition. A full coarse-grid FDTD algorithm is then implemented without additional grid refinements for the insulation, the resistive loading and the feed line. As a function of insulation properties and resistive loading profiles, the transient reflected feed voltage and the input impedance of antennas are calculated numerically. The validity of the proposed model is proved by comparing it with the results of the full fine-grid FDTD.     

Design of multi-frequency microstrip antennas using multiple rings

An electromagnetically coupled feed arrangement is proposed for simultaneously exciting multiple concentric ring antennas for multi-frequency operation. This has a multi-layer dielectric configuration in which a transmission line is embedded below the layer containing radiating rings. Energy coupled to these rings from the line beneath is optimised by suitably adjusting the location and dimensions of stubs on the line. It has been shown that the resonant frequencies of these rings do not change as several of these singlefrequency antennas are combined to form a multi-resonant antenna. Furthermore, all radiators are forced to operate at their primary mode and some harmonics of the lower resonant frequency rings appearing within the frequency range are suppressed when combined. The experimental prototype antenna has three resonant frequencies at which it has good radiation characteristics.     

一种新型复合左右手负阶谐振天线的设计

为了获得高增益小尺寸天线,通过在基片集成波导上引入二阶Hilbert分形缝隙,提出了一种新型复合左右手传输线.在等效电路模型的基础上,利用HFSS和Serenade软件对该传输线的电路参数进行了提取;利用MATLAB语言给出了该传输线的色散曲线;最后,由该传输线设计了终端短路的缝隙天线.实验结果表明：该天线馈电网络简单,工作在复合左右手传输线的-1阶模式上,比之前报道的复合左右手谐振天线具有更小的电尺寸和更高的增益.由于这些性能,使得该天线可以用于无线通信系统中.     

Dual layer stacked rectangular microstrip patch antenna for ultra wideband applications

An antenna consisting of a U-slotted rectangular microstrip patch stacked with another patch of a different size on a separate layer is presented and its performance results are investigated. An equivalent circuit model of this stacked patch design structure is also presented based on an extended cavity model to predict the input impedance. The theoretical input impedance is evaluated from this circuit model and the experimental results support the validity of the model. In this case, stacking with a simple patch adds another resonance to the antenna thus providing a wider bandwidth. The dimension of the top patch is optimised to achieve ultra wide bandwidth. A maximum impedance bandwidth of 56.8% is achieved using this structure, and the return loss |S₁₁|of the antenna is less than -10 dB between 3.06 and 5.49 GHz and the radiation patterns are found to be relatively constant throughout the band. A coaxial feed with Gaussian modulated pulse is used for this antenna.     

Wire antenna versus modified transmission line approach to the transient analysis of grounding grid

The paper deals with transient analysis of grounding grids using two different approaches, wire antenna theory and modified transmission line model. The Pocklington integro-differential equations, in frequency domain, arising from the wire antenna theory are numerically handled via the Galerkin–Bubnov variant of indirect Boundary Element Method (GB-IBEM), while the transient response was obtained using inverse Fourier transform. The modified transmission line equations are treated using the finite difference time domain (FDTD) method. Some illustrative numerical results are presented and discussed in the paper.     

Size reduction and bandwidth enhancement of snowflake fractal antenna

A new small-size and wideband fractal antenna in the shape of a snowflake is proposed. Various iterations of this fractal antenna with probe feed and capacitively coupled feed are compared and an optimised design is presented. It is shown that, with an air-filled substrate and capacitive feed, an impedance bandwidth >49% and, with a slot-loading technique, a reduction of about 70% in patch surface size compared with an ordinary wideband Koch fractal antenna are achievable. The simulation via a finite-element programme, and measured results on the return loss and the E and H-plane radiation patterns of the proposed antennas are presented and shown to be in good agreement.     

Wideband stair-shaped dielectric resonator antennas

Wideband stair-shaped dielectric resonator antenna (DRAs) are designed. Wide bandwidths are achieved with one-step or two-steps stair geometries. Cricular and square cross-sections are discussed with two different excitation methods: coaxial feed and aperture coupled. The DRAs are designed in the X-band. An impedance bandwidth (S₁₁<-10 dB) of 54.3% is obtained with the two-steps stair-shaped DRA. The antennas have broadside radiation patterns in all cases across the matching band. In addition, embedding the base into another dielectric material reduces the size of the stair-shaped DRA. Simulation results are compared with measurements and reasonable agreement is obtained     

Robust Prediction of the Bandwidth of Metamaterial Antenna Using Deep Learning

The design of microstrip antennas is a complex and time-consuming process, especially the step of searching for the best design parameters. Meanwhile, the performance of microstrip antennas can be improved using metamaterial, which results in a new class of antennas called metamaterial antenna. Several parameters affect the radiation loss and quality factor of this class of antennas, such as the antenna size. Recently, the optimal values of the design parameters of metamaterial antennas can be predicted using machine learning, which presents a better alternative to simulation tools and trial-and-error processes. However, the prediction accuracy depends heavily on the quality of the machine learning model. In this paper, and benefiting from the current advances in deep learning, we propose a deep network architecture to predict the bandwidth of metamaterial antenna. Experimental results show that the proposed deep network could accurately predict the optimal values of the antenna bandwidth with a tiny value of mean-square error (MSE). In addition, the proposed model is compared with current competing approaches that are based on support vector machines, multi-layer perceptron, K-nearest neighbors, and ensemble models. The results show that the proposed model is better than the other approaches and can predict antenna bandwidth more accurately.     

An investigation into measurement of handset antennas

This paper describes the investigation into the effects of signal cables on the operating frequencies, radiation patterns, and gains of handset antennas under test by using a proposed testing scheme. In this simple testing method, a coaxial signal cable feeds the handset antenna under test through a microstrip transmission-line etched onto a printed circuit board. The studies of the influences of different feeding schemes and cable arrangements on two commonly used handset antennas are carried out experimentally and numerically. Also, the distributions of the fields close to the antenna, handset chassis, and the cable are measured and simulated to explore the cable-related influences.     

Circularly polarised proximity-fed microstrip antenna with polarisation switching ability

The authors propose a design of a circularly polarised proximity-fed microstrip antenna having polarisation switching ability. The proposed antenna has a simple structure, consisting of a truncated-corners square patch in the same plane with a microstrip feed line extended beyond the patch edge, pin diode and a pad connected to a ground by a conducting post. The diode, which is inserted between the end of the feed line and a pad, is used to control feed line termination. By turning the diode on or off, this antenna can radiate either right hand or left hand circular polarisation. Furthermore, we present a technique to improve the input characteristics of the antenna. It involves two diode-controlled tuning stubs connected in shunt with the feed line. Finally, a discussion on how the diode characteristics affect the structure and results of the antenna is given. All analyses are carried out using finite-difference time-domain technique and confirmed by measurements in the 5 GHz band. A good agreement between the simulated and measured results was obtained     

Rectangular microstrip antennas

Abstract

The theory of rectangular microstrip antennas based on the line resonator model and the cavity model are summarized. The theoretical and experimental values of input impedance and radiation patterns are compared, and the discrepency between these two values are explained. A parallelogram microstrip antenna is constructed, and the input impedances are compared to those of the rectangular microstrip antenna.     

Multilevel spatial modulation

In this paper, a new Multilevel Spatial Modulation technique is proposed. It combines computationally efficient multilevel oding and spatial modulation based on trellis codes to increase coding gain, diversity gain, and bandwidth efficiency. The trellis complexity of the single-stage system increases exponentially, whereas in the proposed multilevel system the complexity increases linearly. The proposed system is analyzed with optimal Viterbi and suboptimal sequential decoding algorithms. The results show that sequential decoding saves 75% of the computational power with a loss of 2 dB SNR approximately, when compared with optimal Viterbi decoding, over both fast- and slow-fading channel conditions. Since the antenna index is used as a source of information in spatial modulation, the number of antennae required increases with the throughput and packing a large number of antennas make cross-correlation unavoidable. In this paper, a low complexity modified decoding technique is also proposed for the multilevel spatial modulation system, in which the correlated received signals are equally combined and decoded by the multistage decoder using the Viterbi algorithm. This technique exploits the receiver antenna correlation and makes the decoding complexity independent of number of antennas. The simulation results indicate that the proposed low complexity algorithm gives approximately 8–10 dB gain when compared with optimal Viterbi decoder with equivalent computational complexity when the eight highly correlated signals are equally combined. This may be a suitable solution for mobile handsets where size and computational complexity are the major issues.     

An Optimized Ensemble Model for Prediction the Bandwidth of Metamaterial Antenna

Metamaterial Antenna is a special class of antennas that uses metamaterial to enhance their performance. Antenna size affects the quality factor and the radiation loss of the antenna. Metamaterial antennas can overcome the limitation of bandwidth for small antennas. Machine learning (ML) model is recently applied to predict antenna parameters. ML can be used as an alternative approach to the trial-and-error process of finding proper parameters of the simulated antenna. The accuracy of the prediction depends mainly on the selected model. Ensemble models combine two or more base models to produce a better-enhanced model. In this paper, a weighted average ensemble model is proposed to predict the bandwidth of the Metamaterial Antenna. Two base models are used namely: Multilayer Perceptron (MLP) and Support Vector Machines (SVM). To calculate the weights for each model, an optimization algorithm is used to find the optimal weights of the ensemble. Dynamic Group-Based Cooperative Optimizer (DGCO) is employed to search for optimal weight for the base models. The proposed model is compared with three based models and the average ensemble model. The results show that the proposed model is better than other models and can predict antenna bandwidth efficiently.     

Realisable rational function approximations for the equivalent circuit modelling of broadband antennas

The vector fitting (VF) algorithm is applied to the equivalent circuit modelling of an antenna over a broad frequency band. To ensure that the resulting circuit model is realisable, the passivity constraint must be imposed during the modelling process. Three methods are investigated to ensure the passivity, each based on VF: (i) the use of quadratic programming proposed earlier by Gustavsen and Semlyen, (ii) a technique based on constraining a second-order rational function and (iii) a search method using a particle swarm optimisation with constraints. These techniques are evaluated through three sample antennas: a commercial broadband horn, an ultra-wideband planar monopole with a notch-band and an active integrated microstrip antenna. The results are compared in terms of the modelling error against the model order and the computation time required.     

A Compact Rhombus Shaped Antenna with Extended Stubs for Ultra-Wideband Applications

Ultra-wideband (UWB) is highly preferred for short distance communication. As a result of this significance, this project targets the design of a compact UWB antennas. This paper describes a printed UWB rhombus-shaped antenna with a partial ground plane. To achieve wideband response, two stubs and a notch are incorporated at both sides of the rhombus design and ground plane respectively. To excite the antenna, a simple microstrip feed line is employed. The suggested antenna is built on a 1.6 mm thick FR4 substrate. The proposed design is very compact with overall electrical size of 0.18λ × 0.25λ (14 × 18 mm²). The rhombus shaped antenna covers frequency ranging from 3.5 to 11 GHz with 7.5 GHz impedance bandwidth. The proposed design simulated and measured bandwidths are 83.33% and 80%, respectively. Radiation pattern in terms of E-field and H-field are discussed at 4, 5.5 and 10 GHz respectively. The proposed design has 65% radiation efficiency and 1.5 dBi peak gain. The proposed design is simulated in CST (Computer Simulation Technology) simulator and the simulated design is fabricated for the measured results. The simulated and measured findings are in close resemblance. The obtained results confirm the application of the proposed design for the ultra-wide band applications.     

A Time Domain Equivalent Source Model of an Impulse GPR Antenna Based on Measured Radiation Fields

Ground Penetrating Radar (GPR) is a valuable tool for determining bridge deck health. The ability to simulate scattering from bridge deck elements and the complex interactions between them, as well as from changes due to the presence and relative location of defects is important for understanding observed responses. These simulations can be performed using electromagnetic computational modeling techniques such as Finite-Difference Time Domain (FDTD). In order to accurately model the GPR investigation, it is necessary to have a time domain equivalent source model that can launch and receive electromagnetic waves into the computational space that replicates the signals transmitted and received by the physical GPR antenna. However, due to complexity of design and proprietary information, the GPR unit is typically very difficult, or even impossible, to fully model with sufficient detail. For bridge deck applications, simulation in two-dimensions adequately captures much of the three-dimensional scattering. Two-dimensional simulations have significant computational savings over three-dimensions, and are more feasible to be iteratively implemented to solve inverse problems. The work presented here uses experimental results and presents a computational approach to determine the characteristics suitable for excitation of a two-dimensional FDTD model.     

New CPW-fed monopole antennas with both linear and circular polarisations

A low-profile, planar, circularly polarised monopole antenna with a shorting sleeve strip fed using a coplanar-waveguide transmission line for wireless communication in the digital communication system and the global positioning system bands is studied. By utilising the coupling effect between the monopole antenna and sleeve, two excited resonant modes, including the monopole and travelling-wave modes, cover the 1.57- and 1.8-GHz bands. Through modification with antennas of various geometrical parameters, the proposed antenna exhibits the wide bandwidth in the desired frequency bands, which has a bandwidth of 45% at 1.6%GHz for an input reflection coefficient of less than %10%dB. Meanwhile, the antenna has a 3-dB axial ratio bandwidth of 5%. Details of the design considerations for the proposed antennas are described, and the results of the antenna performances obtained are presented and discussed.     

功率吸收钳校准数学模型

在研究偶极子天线辐射的Sommerfeld半空间模型基础上，通过对构造模型的边界条件的改进，提出了建立功率吸收钳校准系统的新方法。它将一个复杂的开放系统的近场辐射问题转化为一个传输线路问题，用经典的传输线理论进行计算，建立了严格的吸收钳校准的数学模型，并给出相应的等效电路，数学模型的计算结果与实际校准的结果能很好符合，理论计算结果有较高的参考价值。     

基于矩量法对分段指数电阻加载Koch分形天线阻抗特性研究

提出一种新的分段指数电阻加载Koch分形偶极天线，其加载电阻沿天线从馈电点按指数规律递增．基于矩量法（MOM）分析计算其阻抗特性，结果表明，该天线能满足现代通信系统对天线小型宽带的要求，也为分析设计小型宽带天线提供了一种有效的方法与思路．     

两种天线方案抖振位移响应的比较研究

本对置于某一超高层建筑顶部的钢质天线抖振响应进行了研究。对两种天线单体方案的抖振性能进行了气动弹性模型试验和理论计算和比较，最后分析了天线的鞭稍效应。计算和试验结果为天线结构的分析设计提供了依据。