FDTD calculation of wide-band antenna gain and efficiency

Absolute gain and radiation efficiency are calculated using the finite-difference-time-domain (FDTD) method. The method described utilizes pulsed excitation, so that wideband results are available from a single FDTD computation. The approach is demonstrated for a simple wire antenna geometry, and is validated by comparison with results obtained using the method of moments     

The input impedance of a monopole antenna mounted on a cubical conducting box

An experimental investigation has been performed to determine the input admittance characteristics of a monopole antenna mounted on a conducting cubical box over a ground plane. Input admittances of monopoles from 2 to 6 cm long mounted on a 10 cm box were considered in the investigation so that effects of changes in the electrical size of the box could be evaluated. The monopoles were placed at various points to determine the functional dependence of input admittance on the position of the monopole antenna. A numerical analysis of the radiating structure was performed using the method of moments to compare the experimental data with the computed input admittance. This comparison and the observed empirical behavior of the input admittance were then utilized to predict the effects of the conducting box on the overall admittance of the radiator.     

Calculation of the radiation pattern, gain and input impedance of a Yagi antenna

A computer program is presented for the calculation of the radiation pattern, gain and input impedance of a Yagi antenna having up to ten elements.     

基于FDTD的太赫兹光导天线三维辐射特性计算方法

光导天线是目前产生和探测太赫兹波最常用的辐射源之一,在太赫兹成像、光谱检测等诸多领域有着广泛的应用前景。本文介绍了基于时域有限差分(FDTD)的太赫兹光导天线三维辐射特性计算方法,在分析光导天线辐射原理的基础上阐述了半导体漂移电流、扩散电流对电场及磁场的作用,并根据实际运用情况对漂移方程、连续性方程进行简化,最终求得电流密度、电场、磁场的迭代方程,给出了光导天线辐射特性计算流程。     

Calculation of radiation patterns of a Yagi antenna above imperfectly conducting ground

A computer program is presented for the calculation of radiation patterns of Yagi antennas, having up to ten elements, located above a plane imperfectly conducting ground.     

Input impedance of a dipole antenna above a conducting half space

The derivation of an expression for the change in free space input impedance of a finite horizontal dipole, due to the proximity of a conducting half space, is outlined. The impedance change is expressed in a conveniently computable form in terms of the Fourier transform of the antenna current distribution. Using available transforms some typical results are shown over a 50:1 frequency range.     

Radiation patterns of an antenna near a conducting strip

Horizontal patterns of a linear antenna near a conducting strip are found by solving a two-dimensional problem using an integral equation method. Because of practical interest, the computed patterns are shown for only small to moderate sizes of the strips and small to moderate separation distances of the antenna.     

Evaluation of antenna radiation Q using FDTD method

A new and simple method is proposed for determining the radiation Q of an antenna using the finite difference time domain (FDTD) method. The numerical results are compared with analytical formulas and good agreement is reported.     

柱形等离子体天线阻抗及辐射特性实验研究

借助天线测试系统,实验研究了柱形等离子体天线的阻抗特性和辐射特性。实验结果发现:该柱形等离子体天线与相同构造和尺寸的金属天线相比,具有较好的宽带阻抗特性;柱形等离子体天线的相对增益在50~260MHz频带范围内与金属天线相差不大;等离子体发射天线相对增益略高于等离子体接收天线。     

Enhancement of gain and radiation bandwidth for a planar 1-D EBG antenna

This letter describes a technique to increase the radiation bandwidth and the gain of a classical planar electromagnetic band gap (EBG) antenna. Those two parameters are relative to the EBG material but also to the excitation, this second characteristic is studied here. The principle is to excite the EBG structure with several sources (instead of a single one classically). The performances depend on the number of sources and their spacing. Directivity and radiation bandwidth can be increased dramatically with few sources.     

Input impedance, radiation pattern, and radar cross section ofspiral antennas using FDTD

A finite-difference time-domain (FDTD) analysis of spiral antennas is performed to calculate input impedance, antenna gain, and scattering. A semicircular spiral mounted on a dielectric substrate was simulated for computing the input impedance versus frequency. The gain and scattering computations were performed on a square Archimedean spiral mounted in a ground plane with a cavity backing. Total-field FDTD calculations are used to compute the impedance and gain patterns, while a specially modified scattered-field approach for aperture antennas in infinite ground planes is used for the scattering results. Comparisons are made with published impedance measurements and gain and scattering calculations done with a finite element method. Good results were obtained for impedance, radiation, and scattering     

The input impedance and the antenna gain of the spherical helicalantenna

The input impedance and the antenna gain of the spherical helical antenna are obtained theoretically and experimentally. Results indicate the better performance of the 3-turn antenna over the 7-turn one in terms of the impedance bandwidth and the stability of the antenna gain. The theoretical current distribution is also obtained and its salient characteristics are discussed     

Effect of disc reflectors on radiation impedance of short-backfire antenna

Using near-field analysis, the influence of large and small disc reflectors used in short-backfire antennas on the radiation impedance of a dipole feed element has been investigated. The effect of each reflector is evaluated separately, and the overall change in the radiation impedance of the dipole is predicted.     

The radiation pattern of a monopole antenna attached to aconducting box

A system investigation was undertaken to determine the radiation patterns of a monopole antenna mounted on a cubical conducting box over a ground plane. The effects of the location of the monopole and the electrical size of the box were noted as compared to similar patterns measured over a flat ground plane. Experimental results were also compared with numerically predicted values obtained from a method of moments patch code. It was concluded that the location at which a monopole antenna is mounted on a conducting box and the electrical size of the box clearly affect the overall radiation pattern of a monopole antenna. In general, mounting the antenna away from the center of the box will increase the depth of the nulls     

Consideration of antenna gain and phase patterns for calibration ofpolarimetric SAR data

A general polarimetric model for orbital and Earth synthetic aperture radar (SAR) systems that explicitly includes key radar architecture elements and is not dependent on the reciprocity assumption is developed. The model includes systems whose receiving configuration is independent of the transmitted polarization (one configuration), as well as systems with two distinct receiving configurations, depending on the commanded transmitted polarization (H or V). Parameters that are independent of target illumination angle and those with illumination angle dependence are considered separately, allowing calibration approaches which are valid for targets at different illumination angles. The calibration methods presented make use of the model linearity to provide tests for the radar model accuracy and for SAR data quality. X-band polarimetric SAR are used to validate the theory and illustrate the calibration approach. The extension of the model and calibration method to other radar systems is discussed     

E-shaped patch with reactive impedance surface for high gain and broadband circularly polarized antenna

A low-profile circularly polarized (CP) antenna with high gain and broad bandwidth is aimed at 5-GHz Wi-Fi applications using a symmetrical E-shaped patch. Initially, the radiating element is modeled as a symmetrical E-shape. An array of 4 × 4 rectangular patches are arranged periodically to make up a reactive impedance surface (RIS) structure. Furthermore, the RIS structure is deployed in the middle of a symmetrical E-shaped radiating patch and a perfect electric conductor (PEC) ground plane. As a result, the broadband CP is achieved with high gain. The above-mentioned combinations have achieved a −10-dB reflection coefficient bandwidth of 21.4% (4.92–6.1 GHz) and a 3-dB axial ratio (AR) bandwidth of 15.5% (5.25–6.1 GHz), and the antenna has attained a gain of 7.45–7.53 dBic.     

Improvement of microstrip patch antenna radiation patterns

Microstrip patch antennas typically have radiation patterns containing unwanted sidelobes or local minima caused by surface waves, especially when fabricated on high dielectric-constant substrates. The paper shows that removal of the substrate beneath the patch can greatly improve the pattern. A variation of this technique, compatible with monolithic fabrication, is applied to fabrication of a patch on GaAs and shows similar pattern improvement     

应用矩量法对任意线天线辐射特性的分析

采用矩量法对线形导体上的辐射特性进行了分析，该方法是基于伽略金法，以三角矢量函数作为空间的基函数和检验函数对任意形状的线结构的电场积分方程进行求解，并以此求解天线上的电流分布和天线的功率辐射方向图。给出了篇例，结果表明，该方法是有效的，为超宽带天线的分析奠定了基础。     

New analytical input impedance calculation for fast design of printed narrow slot antenna

In this article, fast and simple closed-form relations are presented to calculate input impedance of filamentary-excited printed narrow slot antenna on electrically thin dielectric substrate near to half wavelength resonance frequency. This antenna is a complementary structure of thin printed dipole antenna. The obtained formulations have been verified numerically by a commercially available full-wave electromagnetic simulator and then a prototype antenna has been produced. Experimental measurements are realised on the antenna and these measurement values of input impedance also have verified analytical relations and numerical simulations. It is shown that analytical, numerical and experimental results are close to each other. Therefore, these relations can be utilised as an initial design step just before making detailed numerical analyses. Besides, the given relations can be easily realised in CAD-oriented platforms for fast calculations.