模式匹配与积分方程在HPM模拟中的应用

针对具有电大尺寸、厚介质罩且馈源采用特定模式激励的高功率微波(HMP)传输及辐射结构研究了一种新型的电磁建模技术。将模式匹配方法与积分方程方法进行混合,构建了电磁模型的方程组,采用多层快速多极子技术、预条件器等进行求解加速,最终形成了可对电大尺寸HPM传输、辐射系统进行高效全波电磁仿真的技术。以电大变张角喇叭馈源、功率合成天线、波束波导及波束波导天线作为实例,构建了几何及电磁模型,并进行了包括远区方向图、近区功率密度分布在内的数值模拟,对该技术的正确性和通用性进行了验证。结果表明,该技术边界拟合准确,内存消耗低,且对馈电模式能予以准确反映,适用于HPM传输发射的高效高精度模拟。     

求解波束波导中激励-传输-辐射问题的积分方程方法

针对波束波导系统结构和馈电特性,应用体面积分方程建立了任意结构波束波导中电磁波的激励、传输和辐射问题所对应的物理模型.在激励端,采用模式展开方法描述输入口面场分布,并利用模式匹配方法精确模拟波束波导馈电端的匹配状况.通过对波束波导内部的实际结构的精确拟合,基于积分方程建立了激励-传输-辐射的电磁模型,并以高效数值解法给...     

基于混合场积分方程的半空间上方金属目标电磁散射特性高效分析

研究一种可以高效求解半空间金属目标电磁散射积分方程方法,电场积分方程适用于任意结构电磁问题分析,但是生成的矩阵条件数大,迭代求解收敛性差;而磁场积分方程生成的矩阵条件数小,迭代收敛性好,但是仅能分析闭合结构问题,本文采用了混合场积分方程方法,同时具备电场积分方程的普适性与磁场积分方程的收敛性.由于混合场积分方程中涉及格林函数的梯度项,为了进一步加快计算效率,本文引入了一种针对半空间格林函数的高效四维空间插值方法,对组成半空间格林函数的索末菲积分进行列表和Lagrange插值,以实现高效的迭代求解,效率在传统混合场积分方程的基础上提高12.6倍.数值结果表明,该方法在保证精度的同时,可以显著降低求解问题的时间.     

基于磁荷面分布的舰船磁场预测方法

利用等效源观点, 把钢铁建造的舰船船体视为等效磁荷面分布, 建立了该分布与磁场传感器测量值之间应满足的第一类Fredholm积分方程, 然后利用广义逆矩阵对积分方程离散化后得到的线性方程组进行求解, 并以矩阵条件数来衡量方程组的病态程度, 最后利用求解得到的磁荷分布来预测舰船在空间中任意点上产生的磁场. 数值模拟表明该方法可以准确地识别磁性从而得到精确的磁场预测值. 最后利用一个船模实验验证了本方法. 关键词： 舰船 磁场 磁荷 积分方程     

单极性亚纳秒脉冲激励口径的辐射特性

 通过解析积分运算，获得了阶跃脉冲激励口径天线瞬态辐射场的解析表达式, 分析了辐射电场脉冲的持续时间与口径尺寸、观察距离及观察角度的关系。研究了在高斯脉冲激励下口径辐射场特性的分析方法，并探讨了脉冲口径天线主轴方向上辐射场的分区依据。     

光在光轴取向任意条件下的晶体表面透射率

为了分析一束光在晶体表面的能量损失以及两束折射光的能量比,给出了一种求解反射率和透射率的方法。讨论了光从各向同性介质入射到单轴晶体表面时的折射和反射,注意到了e光线与e光波方向的不同,e光折射率与e光波法线折射率的不同,得出了在界面处应该满足的边界方程。在晶体光轴取向任意的条件下,给出了表明各光束间能量关系的折射率和反射率的理论表达式,为晶体器件特性的研究提供了有力的理论工具。数值模拟表明:得到的结果满足能量守恒;反射到各向同性介质中的光的电场(或磁场)与原入射光的电场(或磁场)不再平行;光轴的取向和入射角的大小对折射的o光、e光的能量比有很大的影响。     

计算涡旋电场的二种方法

对于满足似稳条件的、由变化磁场所激发的涡旋电场,本文介绍了从场方程的微分形式及积分形式出发进行求解的方法.并对二种典型情况作了分析、计算.     

高频电磁波多次散射的数值求解

结合等效射线管模型和物理光学法实现了复杂目标高频电磁波多次散射高效且精确的数值求解.在求解射线管的电磁场积分中，选取物体表面为积分区域，详细推导了在物体表面完成的远场积分公式，数值计算结果比前人沿射线管波前积分更精确.计算了几种由平板构成的导体和涂覆介质目标，数值求解结果与已有的实验数据相当符合.该结果可为复杂目标的雷达探测和识别提供理论参考. 关键词： 电磁散射 电磁场积分方程 物理光学法     

基于积分方程法和奇异值分解的磁性目标磁场延拓技术研究

对磁性目标磁场延拓技术进行了研究,提出了一种基于积分方程法和奇异值分解的新方法.应用该方法只需要采用积分方程法对磁性目标的结构进行较为粗略的单元划分,利用目标下方大平面上的磁场测量值,得到相应的线性方程组.采用基于奇异值分解的截断奇异值方法和修正奇异值方法对该线性方程组进行正则化求解,可实现磁性目标磁场的三维磁场重建、向上或向下延拓.该方法较以前的方法,提高了磁性目标磁场延拓的精度和可靠性,并且解决了磁性目标磁场在一定范围内向上延拓的技术难题. 关键词： 磁性目标磁场 延拓 积分方程法 奇异值分解     

大型双反射面天线近轴区辐射FDTD-TDPO模拟

针对大型双反射面天线尺寸过大、使用单一的时域方法无法单独模拟其远区辐射特性,以及使用单一的高频近似技术无法给出准确结果的局限,给出了用于大型双反射面天线时域辐射模拟的并行时域有限差分(PFDTD)-并行时域物理光学(PTDPO)混合方法。先创建两个用于并行计算的进程组,一个用于PFDTD计算,另一个用于PTDPO计算; 再根据PFDTD方法计算出双反射面天线馈源的近磁场,同时根据这些磁场使用基尔霍夫表面积分表达式(KSIR)并行计算出次反射面上及其附近的磁场,再使用KSIR并行计算出主反射面上的磁场; 最后使用PTDPO方法计算出双反射面天线的远区辐射场的瞬态响应。同时,还给出主反射面口径为40个波长的Cassegrain双反射面天线的算例,并对馈源相同而口径尺寸不同的双反射面天线进行近轴区的时域辐射模拟。     

机载多天线系统电磁兼容性研究

为了在有限计算机资源条件下快速解决机载平台中多天线系统的电磁兼容(EMC)问题,基于电场积分方程(EFIE),实现自动分层的多层快速多极子方法(MLFMA).针对天线问的近场耦合特性,采用任意天线间的隔离度代替传统隔离度,使得隔离度计算结果更加合理.同时采用BiCGStab(l)结合近场预条件方法进行求解,进一步提高MLFMA的综合效率.最后实例计算并分析波音747飞机模型上多根超短波天线的辐射方向图和宽频带内天线间的隔离度.数值结果表明方法准确有效.     

Level-set based topology optimization for electromagnetic dipole antenna design

This paper presents a level-set framework for a typical electromagnetic design problem of dipole antenna. In this study, the geometrical configuration of an antenna is represented by the zero-level contour of a higher-dimensional level-set function. The governing equation for the induced current flow on a metal surface is the Electric Field Integral Equation (EFIE), which takes into account the electric component of the incident wave. The design objective is formulated in terms of the surface current and incident electric field. The normal velocity of the level-set model, which reflects the sensitivity of the objective function, is derived from the adjoint variable method and shape derivative. By optimizing the objective function, the area with the highest current density, to which the voltage feeding should be applied, can be reshaped. The advantages of adopting the level-set technique for electromagnetic design lie in its capacity for capturing sophisticated topological changes and facilitation in mathematical representation of the design configuration. The demonstrative examples of dipole antenna design show that the level-set method results in a fairly smooth optimization process, where the vacuum/metal interface gradually attains its optimal configuration. A series of design cases with self-adjoint and non-self-adjoint sensitivity analyses are studied and compared to the benchmarking problems in dipole antenna.     

Multimode network analysis for dielectric leaky-wave antennas consisting of multilayer periodic structure with arbitrary dielectric distributions

The multimode network method is used to analyze the radiation characteristics of the leaky-wave antenna consisting of multilayer dielectric periodic structure with arbitrary dielectric distributions in each layer. The eigenfunction of each periodic layer is determined by Floquet theorem; and the mode matching combining with generalized transverse resonant method are used to derive the dispersion equation of the leaky-wave antenna. The complex transmission constant is calculated by Newton iterative method and the radiation characteristics of the antenna are obtained. Some antenna structures are analyzed and useful guidelines for design of the leaky-wave antennas are suggested.     

Radiation characteristics of multilayer periodic dielectric structures

Radiation characteristics of multilayer periodic dielectric structures are investigated by the method which combines the building block approach of multimode network theory with the rigorous mode matching procedure. The multilayer periodic structure is composed of uniform dielectric layers and single periodic layers. Two examples are given in this paper; first, radiation property of the double dielectric grating antenna is analyzed. The results indicate that the double dielectric grating antenna has relatively smaller dimensions than that of the single one. It is undoubtly of great importance in the case that the limitation of the weight and the volume of the system is strictly required. Secondly, some curved profile grating antennas are analyzed by combining the present method with the staircase approximation. In such a way, the effects of groove profile on the performance of the grating antennas are systemetically studied and some useful guidelines for the design of the dielectric grating antennas are thereby suggested.     

Bistatic electromagnetic scattering from a three-dimensional perfect electric conducting object above a Gaussian rough surface based on the Kirchhoff–Helmholtz and electric field integral equation

A hybrid integral equation is developed to solve the problem of electromagnetic (EM) scattering from a three-dimensional (3D) perfect electric conducting (PEC) object above a two-dimensional (2D) PEC or dielectric Gaussian rough surface. Firstly, the Kirchhoff–Helmholtz (KH) equation is adopted to describe the wave reflection on the rough surface; only one integral operation on the rough surface is needed, and the scattering from the object can be described by solving the electric field integral equation (EFIE) on the surface of the object. Moreover, according to scattering theory, the KH equation and the EFIE are coupled together (KH-EFIE) to describe wave propagation between the object and the rough surface. Then method of moments (MoM) is adopted to solve the KH-EFIE, and the current is obtained to calculate the scattering field. Finally, compared with other methods, the accuracy of the proposed approach is validated, and its efficiency is proved to be much higher than numerical solutions. Furthermore, by calculating the statistic composite radar cross-section (RCS) of the object/surface and the difference radar cross-section (DRCS) of the object, the influence of the rough surface root mean square (rms) height, the correlation length, the medium permittivity, the shape of the object, and the altitude of the object on the scattering characteristic is investigated.     

加载电磁带隙结构的阶梯型微带天线设计及分析

为了减弱大气摩擦引起的高温损伤,航空飞行器雷达天线一般都会加装天线罩或介质窗,将电磁带隙(EBG)结构的禁带特性和阶梯型微带天线的带宽及良好的匹配特性相结合,设计了一种含介质窗的EBG结构阶梯型微带天线,并计算分析了天线的辐射特性及介质窗对辐射特性的影响。结果表明:EBG结构产生的带隙能够制约天线表面波的传播,改善天线的带宽和增益性能,且当介质窗存在时,该结构亦可降低天线与介质窗间的互耦效应。这为含介质窗的EBG结构阶梯型微带天线的设计和应用提供了一定理论参考。     

Brewster Angle Effect on Performances of a New Millimeter Wave Omni-Directional Antenna Gloved with a Dielectric Shell

A new millimeter-wave omni-directional antenna consisting of circular rod corrugations gloved with a dielectric shell operating in the TM₀₁ mode is investigated. As an eigenvalue problem, the antenna is analyzed with the rigorous mode matching method. The radiation characteristics of the antenna are calculated for different parameters with a particular attention directed to the Brewster angle effect on the performances of the antenna. A comparison of the radiation characteristics is made between the antennas with and without dielectric shell. It is found that the introduction of the dielectric shell will change the location where the leakage constant reduced to zero. The effectiveness and reliability of the present analysis are verified by the calculated results given in the literature. Therefore, some useful guidelines for the design of the antenna are thereby suggested.     

Mode Matching Analysis for a New Millimeter Wave Omni-Directional Antenna Consisting of Circular Rod Corrugations Gloved with a Dielectric Shell

A new millimeter-wave omnidirectional antenna consisting of circular rod corrugations gloved with a dielectric shell is investigated. As an eigenvalue problem, the antenna is analyzed with the rigorous mode matching method. The radiation characteristics of the antenna are calculated in the Ka-band frequency range. A comparison of the leaky characteristics is made between the antennas with and without dielectric shell. It is found that the circular dielectric shell layer greatly affects the leaky characteristics of the antenna and the leakage constant increases considerably. In such a way, the length of the antenna can be reduced tremendously with higher radiation efficiency. This fact indicates that the proposed leaky wave antenna is of essentially practical significance for the case where the limitation in size and weight of system is strictly required. The effectiveness and reliability of the present analysis are verified by the calculated and experimental results given in the literature.     

Brewster angle effect on performances of omni-directional periodic rod antenna

An omni-directional periodic dielectric rod leaky-wave antenna operating in the TMoi mode is investigated. As an eigenvalue problem, the structure is analyzed theoretically with mode matching technique. The radiation characteristics of the antenna are calculated for different parameters with a particular attention directed to the Brewster angle effect on the performaces of the antenna; and some usefull guidelines for design of the antenna are thereby suggested.     

近零介电常数材料用于天线口面加载研究

近零介电常数材料常用于口面加载以修正天线波前相位,提高口径效率。在对以往金属线阵周期结构研究基础上,提出了介质镀膜板周期结构的近零介电常数材料,并基于NRW本构参数法计算得到了该材料的等效介电常数,依据口面相位差平方和最小原则研制了中空形式的介质镀膜中空板加载结构。实验结果表明,X波段角锥天线加载后其主轴增益最大提高了1.8 dB,口径效率从原有0.4提高至0.6以上,相对工作带宽大于10%。