行波电流圆环的辐射方向性

具有行波电流分布的圆环天线,是特高频段构成高增益天线系的基本单元天线之一。本文从基本振子的辐射场出发,推导出任意周长圆环的辐射场表达式。在此基础上,得出了行波电流圆环环轴方向辐射圆极化波的条件,讨论了几种工程上常用的典型尺寸行波电流圆环的辐射方向图。     

MATLAB在反射面天线三维方向图中的应用

提出了一种反射面天线三维方向图的绘制方法。介绍了分析反射面天线辐射场的方法,并将表面电流法和口径场法进行了比较。给出了计算抛物面上的电流分布公式,论述了表面电流法的基本原理。运用MATLAB软件对反射面天线的辐射场进行了数值计算,阐述了程序主要语句格式和功能以及计算的流程图,得到了天线的二维和三维方向图,直观清楚地表现出辐射方向图的特点,为绘制反射面天线的方向图提供了一种方法。     

基于MOM的舰船通信天线的特性分析

以舰船通信天线为研究对象，应用网格模型分析法及矩量法（MOM）对其进行计算分析，给出了求解复杂天线问题的一般思路。基于Pocldington积分方程和Galerking法，采用分段正弦函数展开，计算得出此类天线的输入阻抗和辐射方向图，并与无限大导体平面上的天线进行了比较。计算结果反映出了船体对舰船天线本身的影响。     

阵列天线互耦的矩量法分析

文中采用矩量法分析无限大理想导体板上的偶极子天线.利用分段正弦基函数Galerkin法推导出阵列天线偶极子单元的阻抗及电场分布的公式.采用Matlab编程计算了中心单元馈电,其他单元接匹配负载情况下中心偶极子天线在阵中的方向图.     

大型阵列天线辐射的近似分析

将散射矩阵推广到阵列天线的辐射分析当中,推导出阵列天线辐射计算基础理论公式.该公式综合考虑了天线与馈电系统的失配引起的反射、天线单元之间的互耦效应以及天线单元在阵列当中和位于自由空间的辐射特性的变化.采用算例验证了该计算公式的正确性,根据阵列单元的辐射特点和S参数特点,提出了大型阵列辐射场的近似计算方法.以此为基础采用泰勒馈电设计了副瓣电平低于一30dB的大型阵列天线.     

一种贴片阵列天线散射减缩的新技术

引入贴片天线单元渐变开槽的方式来设计低散射阵列天线.通过对不同的单元开不同尺寸的槽,在等幅度馈电的情况下实现远区辐射场的低副瓣特性.对开槽贴片单元进行散射减缩预估,然后将该方法应用于1×9渐变开槽贴片阵列的设计中,与传统阵列天线的单元形式完全一样,采用不等幅馈电实现泰勒远区辐射场相比,该方法不仅实现了远区辐射场的低副瓣,而且实现了天线模式项散射场的低副瓣,同时又兼顾了结构模式项散射场的散射减缩,从而有效地实现了阵列天线的低散射特性.测量结果与原始阵列进行比较,证明了该方法的有效性.     

复杂金属载体上线天线的MoM分析

各类金属载体上线天线的特性分析具有很重要的实用价值。本文运用矩量法处理各种载体上线天线问题。首先将线天线模拟为带状线,天线和载体表面均采用平面三角形单元进行剖分,RWG基函数作电流展开函数。然后介绍了线面连接处贴片单元的剖分方法,以及在连接处定义基函数和添加电压源模型。本文分析了各种形状金属载体上线天线的特性,研究了角度和位置对天线输入阻抗或辐射特性的影响。数值结果验证了方法的正确性。     

基于矩量法对导体板上单极天线特性研究

利用矩量法对有限大导体板上单极天线的阻抗特性进行了研究。基于Pocklington积分方程和Galerkin法，采用分域基正弦函数展开模式，得出了有限尺寸导体板上单极天线的电流分布和输入阻抗，并对单极天线在不同长度及不同导体板上的情况进行了研究。结果表明，单极天线的长度及导体板的形状及大小在一定程度上影响了单极天线的特性。     

基于相位梯度超表面的高增益天线设计

根据广义Snell 反射定律,相位梯度超表面可在其表面形成额外的平行波矢分量,从而对电磁波的反射进行调 控。如果构成反射超表面单元的相位差按照抛物面分布,那么就可以实现对垂直入射电磁波的聚焦;相反,在超表面焦点处放置 辐射球面波的馈源,球面波经超表面反射可以得到平面波,从而提高馈源增益。本文基于有相位梯度的单元,设计了由13×13 个 单元构成的二维反射相位梯度超表面,并在其焦点处放置贴片天线,构成反射面天线。仿真和测试结果都表明,贴片天线辐射的 球面波经超表面反射后得到了平面波,天线的增益达到20 dB,比贴片天线提高了11.7 dB。     

反射面天线散焦特性研究

本文应用球面波展开和面电流积分相结合的方法分析了散焦反射面天线 ,给出了由于馈源系统位置偏差导致的反射面天线散焦的计算公式 ,计算结果与实验数据相吻合。     

The moment method solution for printed wire antennas of arbitraryconfiguration

A printed wire antenna of arbitrary configuration is analyzed. The electric field tangential to the wire is derived using the current expanded by piecewise sinusoidal functions. These functions are also used to form the impedance matrix elements. Use of the stationary phase method leads to a simple expression for the radiation field. Numerical analyses based on the present formulation yield radiation characteristics of a zigzag dipole antenna, a loop antenna, and a round spiral antenna     

Antenna Modeling Based on a Multiple Spherical Wave Expansion Method: Application to an Antenna Array

A method to derive an equivalent radiation source for planar antennas is presented. This method is based on spherical near-field (NF) data (measured or computed) to ascertain an equivalent set of infinitesimal dipoles placed over the main antenna aperture. These produce the same antenna radiation field, both inside and outside the minimum sphere enclosing the antenna. A spherical wave expansion (SWE) of the NF data is written in terms of infinitesimal dipoles using a transition matrix. This matrix expresses the linear relations between the transmission coefficients of the antenna and the transmission coefficients of each dipole. The antenna a priori information are used to set the spatial distribution of the equivalent dipoles. The translational and rotational addition theorems are exploited to derive the transmission coefficients of the dipoles. Once the excitation of each dipole is known, the field at any aspect angle and distance from the antenna is rapidly calculated. Computations with EM simulation data of an antenna array illustrate the reliability of the method.      

介质覆盖导电球上缝隙天线的辐射

给出了用位函数方法推导介质覆盖导电球上缝隙天线辐射场严格解的过程.基于球Hankel函数加法定理,将基本磁流源激励的场展开为以球心为原点的球面波的叠加.利用球矢量波函数的定义及性质,提取出场的径向分量,将初级场分解为相对于径向的TE波和TM波,避免了复杂的矢量微分运算.在此基础上依据散射叠加原理,构造出各区域中场的一般表示形式,其中待定系数直接由球面分层介质中波的反射和透射规律给出.作为实际应用的例子,给出了介质覆盖导电球上均匀环缝问题的计算结果,并对结果进行了分析.     

球面近远场和远近场变换算法

天线的远场对于研究天线辐射特性具有重大意义，近场测量技术因其能够避免直接测量远场而得到广泛应用，该技术采用近远场变换获得远场，然而，检验该远场的准确性也是很重要的.为了解决此类问题，文中以球面近场测量为例，提供了一种解决方案.该方案主要探讨了球面波模式展开理论，该理论是实现球面近远场变换算法的关键，其将待测天线在空间建立的场展开成球面波函数之和，天线的加权系数既包含了远场信息也包含了近场信息.因此，不仅能够利用近场测量信息获得远场辐射特性，同样能够利用远场辐射特性反推得到近场处电场，这样就能检验由近远场变换算法得到的远场是否准确.文中首先推算得到了近远场变换公式，随后进一步推算得到远近场变换的公式，最后将本文算法计算结果与FEKO测量结果进行比较，二者吻合良好，从而证实了本文两种算法的有效性.     

Heat Potential Distribution in an Inhomogeneous Spherical Model of a Cranial Structure Exposed to Microwaves Due to Loop or Dipole Antennas

An inhomogeneous spherical model of a 3.3-cm radius cranial structure is assumed to be placed symmetically in the near field of a small loop antenna or an electrical dipole antenna at 3 GHz. The transitions between the layers are taken to be sharp but sinusoidal. Calculations of the heat potential are performed using a spherical wave expansion technique in which linear differential equations are solved for the unknown multipole coefficients. The results are also compared with the plane-wave excitations. It is seen that a more uniform distribution of the heat potential occurs for the dipole antenna excitation which is also similar to the E-plane distribution in the case of plane-wave excitation. For the loop excitation, a significant hot spot occurs near the center of the structure.     

Radiation resistance of a cylindrical antenna immersed in a weakly ionized magnetoplasma. II†

The field components for electromagnetic and eletromagnetic waves from a cylindrical antenna radiating in a weakly ionized magnetoplasma and expressions for radiation resistances assuming sinusoidal current distribution in the antenna have been obtained. The effect of a steady magnetic field on the radiation resistances has been discussed. it has been concluded that the magnetic field changes considerably the radiation characteristics of an antenna.     

Electromagnetic characteristics of superquadric wire loop antennas

The analysis of antenna configurations in the form of a generalized superquadric loop, which includes circular, elliptical and rectangular loop geometries, is presented in this paper. Use of a Galerkin form of the moment method with piecewise sinusoidal subsectional basis and testing functions provides rapid numerical convergence and accurate representation of the antenna current. A convenient parametric representation for the superquadric curve is developed to allow a subsectional formulation using curved wire segments, rather than the commonly employed piecewise linear segments, to construct the geometry. Both magnetic frill and delta gap source models are implemented to allow a detailed study of input impedance, directivity, radiation pattern and current distribution as a function of various geometrical parameters. The results are shown to compare well with previous results for the special case of a circular loop antenna. Some useful curves are presented to aid in the design of practical superquadric loop antennas     

Electromagnetic radiation of antennas in the presence of anarbitrarily shaped dielectric object: Green dyadics and theirapplications

Although numerical solutions to the electromagnetic scattering by an arbitrarily shaped object have been obtained using Waterman's (1971) T-matrix method (TMM), the general electromagnetic radiation due to an antenna of a three-dimensional (3-D) current distribution in the presence of an arbitrarily shaped object has not been well considered. In this paper, the technique of surface integral equations has been employed; and as a result, a terse and analytical representation of the dyadic Green's functions (DGFs) in the presence of an arbitrarily shaped dielectric object is obtained for the antenna radiation. In a form similar to that associated with the electromagnetic radiation in the presence of a dielectric sphere, the DGFs inside and outside of the object of arbitrary shape are expanded in terms of spherical vector wave functions. However, their coefficients are no longer decoupled due to the arbitrary surface of a 3-D object. The coupled coefficients are then determined using the surface integral equation approach, in a fashion similar to that in the T-matrix method. To confirm the applicability and correctness of the approach in this paper a dielectric sphere, as a special case, is utilized as an illustration. It is found that exactly the same expressions as in the rigorous analysis for the inner and outer spherical regions of the object are obtained using the different approaches. As applications of the approach in this paper, radiation problems of an electric dipole in the presence of superspheroids and rotational parabolic bodies are solved     

The Radiation Properties of a Novel Wire Antenna for the Security Fence Radar

The radiation properties of a novel wire antenna are investigated. The main part of this antenna is a sinusoidal wire undulator, which radiates by coupling electromagnetic energy from a Goubau line located near the antenna. Far-field patterns and S-parameters composed of three sets of antenna are measured. The measured patterns are compared with the calculated ones and the phase and attenuation constants of all the antennas are calculated. Frequency behavior and the dependency on the antenna dimensions of those wave parameters are investigated. Measured and calculated field patterns are also compared with the MoM patterns and some properties of the wave propagating along structure are explained by using MoM current distributions. It is shown that a broadside transversal radiation occurs in a narrow frequency band. The radiation intensity strongly depends on the coupling distance between the Goubau line and the sinusoidal undulator. This antenna is used as the basic element of the security fence radar antenna array working at 1.25 GHz in the L-band, which detects intruders approaching the fence. The performance of the antenna in the array is investigated and the near field distribution of the array is measured. The received signals caused by an intruder are given. The effects of rain and wind are also considered. The results suggests that the security fence radar introduced in this study can be used for the perimeter control of closed areas such as airports, malls, etc.      

Circular polarization microstrip antenna on a conical surface

A theoretical model to analyze the performance of a circular polarization microstrip antenna printed on a conical surface is presented. The radiation pattern of the antenna is simulated by the radiation from its four radiating edges (two axial and two circumferential). The electromagnetic field is expanded in terms of spherical wave modes and it is shown that the circular polarization is obtained by exciting in the antenna two spherical TE_r orthogonal modes with 90° phase difference. The impedance analysis is based on the cavity model. Experimental data fits well the theoretical predictions of the model