三维随机粗糙面上导体目标散射的解析-数值混合算法

提出三维导体目标与导体粗糙面复合散射的解析-数值混合迭代算法,推导出三维目标与粗糙面的耦合积分方程,以及粗糙面散射的Kirchhoff近似(KA)计算式.粗糙面的KA解析计算大大降低了粗糙面求解的复杂度,与目标矩量法的混合迭代保证了计算结果的精度,使得三维体-面目标复合散射计算变得可行.由于体-面两者的高阶耦合作用明显减小,保证了该混合迭代算法的收敛性.与镜像Green函数方法的比较表明该混合算法的有效性,并讨论了粗糙面长度选择对计算结果的影响.结合Monte-Carlo方法,数值分析了理想导体Gauss 关键词： 复合散射 Kirchhoff近似 共轭梯度法 互耦迭代     

Fast iterative approach to the difference scattering from a dielectric target above a rough surface

The difference field RCS (d-RCS) has been defined to analyze the scattering from the target above a rough surface. The electric field integral equations (EFIEs) of the difference induced currentJ _sd on the rough surface, the induced electric currentJ _o and magnetic currentK _o on the dielectric target under a TE wave incidence are derived. A small portion of the rough surface towards the target along the specular direction is taken to compute the scattering contributionE _s0 from the rough surface towards the target, which improves the computation speed. A numerical iterative approach is developed to solve the EFIEs and bistatic d-RCS. The surface length for iterations is dependent on the scattering angle and discussed for comparison with Johnson’s method. Using the Monte-Carlo method to generate the Pierson-Morkowitz (P-M) ocean-like rough surface, bistatic d-RCS of the dielectric target, e.g. a cylinder or a square column, above the rough surface is numerically simulated. The induced electric and magnetic currents on the dielectric target and the difference induced current on the rough surface are numerically discussed.     

Fast iterative approach to the difference scattering from a dielectric target above a rough surface

1 Introduction Electromagnetic scattering from the target above or beneath a rough surface has at- tracted much interest during recent years, because of extensive applications to radar surveillance, target detection, ground radar probing, and so on[1―3]. In order to numeri- cally simulate scattering from composite model of the target and underlying rough sur- face, some fast numerical methods, such as general forward backward method and spec- trum acceleration algorithm (GFBM/SAA)[4,5], fin…     

粗糙面重构问题的混合算法研究

基于Desanto的谱表示法,采用数值和近似算法相结合的混合算法对一维粗糙面的重构问题进行了研究.对于正问题,采用数值算法——矩量法(MOM)得到一维粗糙面的相关散射数据,对于逆问题,考虑不同粗糙度的粗糙面,分别采用两种近似算法——微扰近似(SPA)、基尔霍夫近似(KA)与矩量法的混合算法,对粗糙面轮廓进行了重构;数值结果以高斯粗糙面为例,给出了混合算法对不同粗糙度粗糙面的重构算例,并进行了数据比较和分析. 关键词： 粗糙面重构 矩量法 微扰近似 基尔霍夫近似     

有限元/边界积分方法在海面及其上方弹体目标电磁散射中的应用

本文将有限元/边界积分方法(FE/BIM)结合区域分解方法引入到粗糙海面及其上方目标 的电磁散射问题的研究中. 由于积分边界可以以任意形状设置在距模型表面任意远的距离处, 故本文采用共形人工边界结合区域分解建模方法截断模型的开放计算区域以减少求解未知量, 在截断区域内部采用有限元方法求解, 而计算区域的边界条件通过边界积分方程方法得到. 通过与矩量法获得的数值计算结果进行比较, 证明了该混合算法及模型处理方法的正确性, 进而研究了海面上方弹体目标的电磁散射特性, 并讨论了其双站散射系数随电磁波入射角度、目标高度、海面风速以及弹体尺寸的电磁散射特性变化情况. 本文结果可用于反演复杂背景下的目标信息及目标探测等领域. 关键词： 电磁散射 粗糙海面 目标 有限元/边界积分方法     

Electromagnetic scattering from two-layer rough interfaces in the Kirchhoff approximation

Electromagnetic wave scattering from multilayers consisting of two two-layer Gaussian rough surfaces with lossless media is investigated in the Kirchhoff approximation (KA), with consideration of the shadowing effects. The tapered incident wave is introduced into the classic KA, and the bistatic scattering coefficient is redetermined. The advantage of this method is that it is faster in computation than the exact numerical methods. The numerical results show that the bistatic scattering coefficient calculated in the KA is in good agreement with that obtained by using the method of moment (MOM) over a most angular range, which indicates the validity of the KA proposed in our paper. Finally, the effects of the relative permittivity, the root-mean-square (RMS) height, the correlative length, and the average height between the two interfaces on the bistatic scattering coefficient are discussed in detail.     

Hybrid method for investigation of electromagnetic scattering from conducting target above the randomly rough surface

A current based hybrid method (HM) is proposed which combines the method of moment (MOM) with the Kirchhoff approximation (KA) for the analysis of scattering interaction between a two-dimensional (2D) infinitely long conducting target with arbitrary cross section and a one-dimensional (1D) Gaussian rough surface. The electromagnetic scattering region in the HM is split into KA region and MOM region. The electric field integral equation (EFIE) in MOM region (target) is derived, the computational time of the HM depends mainly on the number of unknowns of the target. The bistatic scattering coefficient for the infinitely long cylinder above the rough surface with Gaussian roughness spectrum is calculated, and the numerical results are compared and verified with those obtained by the conventional MOM, which shows the high efficiency of the HM. Finally, the influence of the size, location of the target, the rms height and correlation length of the rough surface on the bistatic scattering coefficient with different polarizations is discussed in detail.     

Fractal characteristics investigation on electromagnetic scattering from 2-D Weierstrass fractal dielectric rough surface

A normalized two-dimensional band-limited Weierstrass fractal function is used for modelling the dielectric rough surface. An analytic solution of the scattered field is derived based on the Kirchhoff approximation. The variance of scattering intensity is presented to study the fractal characteristics through theoretical analysis and numerical calculations. The important conclusion is obtained that the diffracted envelope slopes of scattering pattern can be approximated as a slope of linear equation. This conclusion will be applicable for solving the inverse problem of reconstructing rough surface and remote sensing.     

粗糙海面及其上方导体目标复合电磁散射的混合算法研究

利用基于电流计算的矩量法结合高频算法基尔霍夫近似的混合算法,分析了一维PM谱粗糙海面及其上方二维无限长任意截面导体目标的双站复合电磁散射特性.混合算法将粗糙面和目标分别划分到KA区域和MOM区域,由于无需数值求解粗糙海面区域的表面极化电流,该算法的运算时间和对计算机内存的需求主要取决于粗糙面上方目标的网格划分情况.数值结果以无限长导体圆柱为例计算了其与一维下垫PM谱粗糙海面的复合双站散射截面,并将计算结果与经典MOM结果进行了比对和验证,结果表明混合方法具有较高的计算效率.最后应用混合方法讨论了不同极化状态、海上不同风速以及目标不同尺寸和位置对复合散射截面的影响. 关键词： 粗糙海面 电磁散射 混合算法 矩量法     

不稳定表面粗糙目标的太赫兹波段散射特性分析

研究了不同粗糙度下的非均匀和分区均匀不稳定表面粗糙导体目标在太赫兹波段的散射特性。区别于采用经验公式的建模方法,提出把随机粗糙面的建模理念应用到太赫兹波段的非均匀和分区均匀不稳定表面粗糙导体目标的建模中,用描述粗糙面的均方根高度和相关长度两个物理量来调节目标表面的粗糙度变化。提出表面粗糙目标的分类形式并给出具体模型,然后用随机高斯粗糙面来模拟非均匀和分区均匀不稳定粗糙目标的表面,再采用物理光学和等效电流相结合的方法来进行仿真计算,分别对不同入射角、不同频率和不同粗糙度的非均匀和分区均匀不稳定表面粗糙导体目标的太赫兹波散射特性进行分析,最后得出了相关的结论。