箔条感应电流分布和散射特性研究

推导了箔条雷达散射截面(RCS)的计算公式及其衍生的公式;基于矩量法和伽略金法,计算和比较了箔条散射与振子辐射的感应电流分布和远场方向图的差异,讨论了箔条空中姿态对感应电流分布及远场方向图的影响;给出了单站散射和双站散射情形单根箔条平均有效雷达截面的定义和计算公式.     

任意形状天线罩的快速分析

将自适应积分算法与体积分方程相结合分析任意形状天线罩对天线辐射特性的影响。将任意形状的天线罩剖分成四面体，基于体积分方程的自适应积分快速算法求出天线罩上的感应电流，即可求出天线-天线罩系统的总场。自适应积分快速算法的应用提高了矩量法的计算速度，并大大缩减了需要的存储量，从而使该方法可用于分析电尺寸较大的天线罩.最后,分别计算了球形、锥形天线罩存在时理想电振子阵列的辐射方向图。     

金属雷电分流条对雷达罩电性能的影响分析

论文建立了天线罩分流条电磁传输研究模型,通过仿真和实验,对比分析了雷电分流条的电磁波传播特性,特别研究了中空十字型和十字型金属分流条的电磁波传输机理,以及金属分流条的材料、长度、宽度、厚度和电磁波不同入射方向对雷达罩电磁波传输性能的影响。研究结果表明:十字型金属雷电分流条对天线罩的电磁传输影响严重,而设计合理的中空十字金属分流条可以有效传输电磁波;另外,金属分流条的厚度和常用金属材料对电磁波传输影响不大,主要影响其导电能力和重量;在保证天线罩雷击安全的前提下,调整金属条长度可以使天线罩电性能达到最佳;金属条的宽度对电磁波传输性能影响明显,宽度越大,天线远场方向图主瓣增益越大;随着入射角的增大,方向图主瓣增益在减小,入射角超过30°时,雷电分流条对天线罩的电磁传输为负影响。     

带罩导弹远场方向图数值仿真中积分域的确定

导弹天线罩是用来保护位于高速飞行的导弹前端的天线系统免受外界影响的一种装置,为研究导弹天线罩对天线性能所造成的影响,该文在运用平面波谱-表面积分法分析天线罩综合电性能基础上,详细讨论了为获取带罩导弹远场辐射方向图所采用的数值算法中的积分区域的确定。     

超高音速GPS天线罩的仿真与分析

超高音速(Ma≥5)雷达天线罩位于飞行器的侧面,一方面起到保护天线罩后面GPS通信天线及接收机的作用,另一方面起到热防、透波的作用,但天线罩的引入势必对GPS天线的辐射和散射特性发生影响。基于几何光学的射线追踪法,分析了GPS平板天线罩的传输系数,利用Ansoft HFSS软件对GPS L1波段微带圆形贴片天线进行加罩仿真分析,给出性能良好的GPS天线罩结构。     

应用PO-AI方法分析加罩OAM天线的辐射特性

应用物理光学-口面积分（PO-AI）方法,数值分析加载天线罩的轨道角动量（OAM）波天线的辐射特性,评判介质天线罩对各阶模式OAM波的辐射特性、幅相分布以及模式纯度的影响程度。通过与现有文献中天线罩实例的测试值相对比,验证了算法的正确性和有效性;考察了开口波导环形阵列OAM波天线工作于不同的模式阶数时,半球形天线罩所引起的空间场幅-相分布的变化。在此基础上,计算了一个正切卵形、多层介质天线罩情况,验证了PO-AI 算法对复杂结构的适应性。从数值结果可见,天线罩对高阶OAM辐射波的幅值分布影响较大。数值计算也证实该算法可以快速预估介质罩存在时OAM波形的畸变程度,有助于实现对天线罩各参数的快速优化。     

频选膜拼接工艺误差对复材天线罩电性能的影响

加载频率选择表面(FSS)薄膜的复合材料天线罩在实际制作过程中,需将若干FSS薄膜结构进行拼接以构成一个整体,FSS膜的拼接工艺误差则对天线罩的电性能产生实质性的影响。文中设计了一款X波段的A夹层平板复合材料天线罩,并建立了由拼接工艺误差带来的FSS膜搭接和FSS膜缝隙的电磁仿真模型,研究了不同拼接工艺对复合材料天线罩的透波率、电磁波传输特性的影响以及对天线辐射特性的影响。研究结果表明：天线罩中的FSS薄膜结构的拼接错位对电磁波传输影响明显,会明显降低天线主瓣增益和天线罩透波率;当入射电磁波的极化方向与FSS薄膜结构的搭接缝方向相同时,FSS膜结构对天线罩透波率影响较大,当极化方向与FSS薄膜结构的搭接缝方向垂直时,则其对天线罩透波率影响较小;两块FSS膜结构边缘搭接的相对位置和搭接距离对天线方向图有明显影响;两块FSS薄膜结构边缘无搭接且存在缝隙则对天线罩透波率影响较小。该研究对复合材料天线罩的制造工艺具有工程指导意义。     

金属空间桁架天线罩分析与研究

金属空间桁架天线罩的电性能影响主要取决于金属桁架的散射特性。文中详细给出了金属空间桁架天线罩的电信设计，并通过一直径7m、工作在20GHz的金属空间桁架天线罩的设计实例和实验研究，实验结果与理论分析相吻合，验证了金属空间桁架天线罩电信设计的正确性。     

运用谱域法分析天线罩对天线方向图的影响

该文利用谱域法分析了天线罩对天线方向图的影响,计算了加天线罩后,天线一天线罩等效体辐射方向图,得到了与实验结果相吻合的结论。并对某型机载吊舱干扰机中天线罩对天线方向图的影响给出了定量说明,为天线、天线罩设计提供了参考依据。     

三维非均匀散射层与其中异常目标的辐射传输

讨论了三维非均匀散射层与其中有异常目标的矢量辐射传输高阶散射与辐射的求解与数值模拟.将三维非均匀散射介质在垂直方位z轴方向划分成许多薄层,再在水平(x,y)方位上划分成方格,用分割形成的各薄盒的零阶热辐射和一阶Mueller矩阵解,推导多阶辐射传输的迭代方法,获得整个散射介质三维VRT方程的高阶散射与辐射解.模拟了微波频段在各空间分辨率的辐射计观测下非均匀植被层和地面上有异常目标的极化辐射亮度温度的观测图像.     

Dielectric space frame radomes for satellite communications

The cross-polarization, signal attenuation and boresight shift for a number of dielectric space frame (DSF) radomes have been investigated using the induced field ratio method. It is shown that DSF radomes produce substantially less cross-polarization than their metal counterparts. It is concluded that in view of INTELSAT's specification of 30.7 dB cross-polar discrimination within an antenna's tracking beamwidth for frequency re-use communication system antennas, DSF radomes, in particular those considered, would not yield appreciable system degradation. The general method presented is extendable to other radomes structures provided that connectivity information is available.     

Analysis of arbitrarily shaped dielectric radomes using adaptive integral method based on volume integral equation

The adaptive integral method (AIM) is employed to solve the volume integral equation (VIE) for analyzing the radiation of the antenna with an arbitrarily shaped radome. Small dipoles are used as exciting sources. Modeling the radomes by tetrahedron cells, the induced volume current is determined by the AIM based on VIE. The application of AIM significantly reduces CPU time and computer memory requirement. Hence, the method presented in the paper can be applied to simulate electrically large sized radomes. Finally, the radiation patterns of small dipole arrays in the presence of spherical and conical radomes are calculated.     

Analysis of a grating metal structure with broad back-scatteringfield pattern for applications in vehicle collision avoidancesystem

In this paper, grating metal structures with broad and flat back-scattering field patterns are studied for possible applications in a vehicle collision avoidance system. The two-dimensional TE scattering of a planar grating structure and a curved grating structure are analyzed at a frequency of 77 GHz. For the planar structure, the method of moments and Floquet's theorem are used to solve the induced current and the resultant back-scattering field. Based on the results of the planar structure, the scattering field of the curved grating structure is obtained by using a perturbation method. The influence on the field pattern of the curvature as well as other structure parameters, such as the width and geometry of each period in the grating structure, is investigated     

双层介质周期漏波天线的辐射特性分析

利用互易性和谱域矩量法研究了具有双层介质衬底的平面二维周期性漏波天线的远区辐射场特性。首先根据互易原理,给出了周期漏波天线辐射远场的计算公式;然后采用整域基函数谱域矩量法计算贴片阵列的散射场,利用反射系数考虑了接地介质板的贡献;最后通过实际算例验证该方法的正确性,并分析介质衬底的介电常数、厚度及频率等参数对远区辐射场特性的影响,给出数值结果。     

Characterization of forward scattering parameters from anarbitrarily shaped cylinder by near-field probing

The forward scattering from an arbitrarily shaped cylinder is characterized by its scattering pattern and the induced field ratio (IFR). Accurate calculation of these parameters for arbitrarily shaped and composite beams is in many cases time consuming, therefore analytical approximations are used. A combined experimental and numerical procedure for evaluation of these parameters based on near-field probing is presented as an alternative. This procedure is shown to be far more accurate than the analytical approximations presently used in calculations of the total scattering effect of tuned sandwich radomes. The results obtained by this method verify well with the scattering characteristics computed analytically or numerically by the method of moments     

辐射场中金属接触无源互调干扰研究

为了评估辐射场中金属接触结构引起的无源互调（passive intermodulation，PIM）对接收天线的干扰程度，提出并验证了一种可以预测被天线接收的PIM幅值的计算方法.应用PIM点源模型，并基于接触结处载波激励电流幅值和PIM信号耦合效率的仿真建立辐射场中金属接触PIM的计算方法；采用缝隙波导工装基于近场耦合测试原理对两根铜丝搭接而成的接触结构在缝隙波导近场辐射场中的三阶无源互调（third-order passive intermodulation，PIM₃）及其按位置分布规律进行测试分析.理论计算和实验测试结果比较吻合，证明本文提出的计算方法能够预估辐射场中金属接触PIM幅值.本研究工作为评估辐射场中PIM产物提供了分析方法，同时有助于深入理解辐射场中金属接触PIM的产生机理.     

Radome crosspolarisation on Intelsat standard 'A' communication satellite antennas

The reduction in size of Intelsat standard 'A' satellite communication antennas from 30.5 m to 15 m in diameter has necessitated the computation of depolarisation effects when the smaller antennas employ metal and dielectric space frame radomes for hardening and protection. Using the standard 15 m antennas enclosed by appropriately scaled-down metal and dielectric space frame radomes, the crosspolar discrimination (XPD) and the boresight shift (BS) have been computed close to antenna axis at 4 and 6 GHz. Comparison with the larger 30.5 m antennas enclosed by 45 m radomes have been made. It is reported that within 0.1 degrees of antenna boresight, the XPD introduced by the radomes does not exceed 33.0 dB as the worst case at 4 GHz. In particular, the Intelsat Specification of 30.7 dB for the XPD within the antenna's tracking beamwidth in clear weather conditions for frequency re-use satellite communication systems is satisfied. The BS is negligibly low.<>     

Electromagnetic scattering from conducting circular cylinders inthe presence of a stratified anisotropic medium-TM case

Scattering by a conducting circular cylinder in the presence of a stratified ferrite medium is investigated analytically using a combined Green's function (G-function) and integral equation approach. The incident plane wave is polarized along the axis of the cylinder. The bias DC magnetic field is in the same direction. The G-function of the structure is developed by well-known techniques of matrix analysis, and the appropriate integral equation for the electric field is derived on the basis of the modified reciprocity theorem. Its solution is followed by numerical results presented in graphical form for both the current density induced on the scatterer's surface and the scattered far field. The possibility of controlling the scattering properties of the structure by varying the degree of anisotropy is also investigated. The main conclusion is that anisotropic materials can be used to control antenna radiation characteristics