【作者】 任新成；

【导师】 郭立新；

【作者基本信息】 西安电子科技大学 ， 无线电物理， 2008， 博士

【摘要】 粗糙表面及粗糙面与目标的复合电磁散射研究在微波遥感、雷达成像、海洋工程、无线通信、表面光学和半导体物理等领域均具有重要的实际应用。本论文就粗糙面电磁散射及其与目标的复合散射中的若干问题开展了系统的理论研究工作。论文首先研究了随机深粗糙度表面、分层介质微粗糙面的电磁散射及粗糙面、分层介质微粗糙面电磁波透射散射。然后将分层介质微粗糙面电磁散射和透射散射的理论运用到海面,研究了基于P-M谱的二维各向异性分层海面、改进的二维分形模型分层海面的电磁散射和透射散射。最后研究了粗糙面与其下方和上方目标的复合电磁散射问题。主要工作和成果如下:1.根据格林矢量第二定理推导出了平面波入射粗糙面时远区场的数学表达式,进一步运用基尔霍夫驻留相位近似法得到了深粗糙度高斯粗糙面双站散射系数计算公式,通过数值计算讨论了深粗糙度高斯粗糙面双站散射系数随介质介电常数、粗糙面相关长度和均方根、入射波频率的变化。2.运用微扰法研究了平面波入射分层介质微粗糙面的电磁散射和透射散射、导出了不同极化状态下的散射和透射系数公式。分别采用高斯和指数型粗糙面来模拟实际微粗糙面,结合它们的功率谱得到了分层介质散射和透射系数计算公式。通过数值计算讨论了底层介质介电常数、中间层介质介电常数和厚度、粗糙面相关长度及均方根、入射波频率对散射和透射系数的影响,分析了两种类型分层介质微粗糙面的电磁散射和透射散射特性。3.从格林矢量第二定理出发,基于微扰法、基尔霍夫驻留相位近似法和基尔霍夫标量近似法分别研究了高斯粗糙面的透射散射问题。数值计算得到了不同极化状态下透射系数随散射角、散射方位角及入射波频率的变化,讨论了介质介电常数、粗糙面相关长度和均方根、入射波频率对不同极化状态透射系数的影响。4.运用分层介质微粗糙面电磁散射和透射散射理论,结合海面P-M谱与改进的分形海面模型导出了二维分层海面散射系数和透射系数计算公式,数值计算并讨论了双站散射系数和透射系数随中间介质介电常数和厚度、摩擦风速、风区范围、观察方向与逆风方向之间夹角和入射波频率的变化,得出了双站散射系数和透射系数的基本特征、分区特征和随频率变化的特征。5.利用矩量法研究了一维高斯和指数型介质粗糙面与其下方二维导体圆柱的复合电磁散射;数值计算并讨论了不同粗糙面相关长度和均方根、粗糙面下方介质的介电常数、导体圆柱埋藏深度、导体圆柱半径下复合散射系数的变化特征。基于矩量法结合近似解析法基尔霍夫近似的混合算法分析了一维导体粗糙面与其上方具有任意形状截面的二维导体目标的复合电磁散射特性,给出了MOM用于求解粗糙面与其上方目标的复合散射的基本原理,通过数值计算讨论了粗糙面相关长度和均方根、导体圆柱半径和高度对复合散射系数的影响。更多还原

【Abstract】 The study of electromagnetic wave scattering from rough surfaces and composite scattering from rough surface with target has been the subject of intensive investigation for its application in a number of important research areas, such as the remote sensing, the radar imaging, ocean engineering, wireless communications, surface optics, as well as the semiconductor physics. This dissertation presents theoretical studies of electromagnetic scattering from rough surfaces and composite scattering from the target below/above the rough surface. The first topic in this dissertation mainly focuses on the scattering from very rough surface and slightly rough surface of layered media, and transmission scattering from rough surface and slightly rough surface of layered media. The theory of scattering and transmission scattering from slightly rough surface of layered media is then extended to rough sea surface, the electromagnetic scattering and transmission scattering from a 2D anisotropic stratified sea surface with P-M spectrum and from the stratified sea surface simulated by an improved 2D fractal model are investigated. Finally, the composite scattering from the target located below and above the rough surface is examined. The main works and results are as follows:1. Mathematic representation of far field with plane electromagnetic wave incidence on the rough surface is derived according to the second Green Vector Theorem. The formula of bistatic scattering coefficient from the very rough Gaussian surface is then obtained by using Kirchhoff stationary phase approximation. The dependence of the bistatic scattering coefficient on the permittivity of medium, the correlation length and root mean square of rough surface, as well as the frequency of the incident wave are numerically discussed.2. The electromagnetic wave scattering and transmission scattering with plane wave incidence on the slightly rough surface of layered medium is studied using the small perturbation method. A Gaussian and an exponential distribution rough surface are presented for describing natural slightly rough surface, the formulae of scattering and transmission coefficient of layered medium for different polarizations are derived in associated with their power spectrum density. The influence of the permittivity of substrate medium, the permittivity and the mean layer thickness of intermediate medium, the correlation length and root mean square of rough surface, as well as the frequency of the incident wave on the scattering and transmission coefficient are calculated and discussed. The characteristic of electromagnetic scattering from two types of rough surface of layered media is analyzed. 3. Based on the second Green Vector Theorem, the electromagnetic wave transmission scattering from the rough surface with Gaussian correlation function is studied with the small perturbation method, Kirchhoff stationary approximation and Kirchhoff scale approximation. The transmission coefficient with different polarization are obtained by numerical implementation for different scattering angle, the scattering azimuth angle and the incident frequency. The influence of the permittivity of medium, the correlation length and root mean square of rough surface, as well as the frequency of the incident wave on the transmission coefficient for different polarizations is discussed.4. The electromagnetic scattering and the transmission scattering from a 2D stratified sea surface with P-M spectrum and improved fractal model are derived by using the theory of the electromagnetic and transmission scattering from rough surface of layered medium. The dependence of the scattering and transmission coefficient on the permittivity and the mean layer thickness of intermediate medium, the friction velocity, the wind field, the angle between observational direction and upwind direction, as well as the frequency of the incident wave are discussed by calculations. The basic characteristic, the zonal characteristic and characteristic with varying of frequency of the bistatic scattering and the transmission scattering are obtained.5. Using Method of Moment(MoM), the composite scattering from a perfect electric conducting(PEC) column located below a Gaussian and an exponential dielectric rough surface is investigated. The composite scattering is calculated and discussed for diffirent correlation length and root mean square of rough surface, the permittivity of medium below rough surface, as well as the radius and buried height of PEC column. A hybrid algorithm, combining analytic Kirchhoff approximation with MoM, is developed to solve the characteristics of composite scattering from a PEC object with arbitrary shape section above a 1D PEC surface. The essential principle of solving composite scattering from a target above a rough surface is presented, the influence of correlation length and root mean square of rough surface, the radius and height of PEC column on the composite scattering are discussed by numerical implementation.更多还原