【作者】 宋运龙；

【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， 硕士

【摘要】 本文首先给出了粗糙面散射的基本理论,讨论了基尔霍夫近似、微扰法和矩量法等粗糙面散射的基本方法。用指数谱粗糙面和高斯谱粗糙面对比说明了地面模拟时选取指数谱的原因,引入了Wang and Schmugge的四成分模型,考虑了不同土壤类型下,土壤湿度与土壤介电常数的关系。根据基尔霍夫标量近似法和驻留相位近似法研究了粗糙面下方介质2中的电磁散射,结合指数粗糙面的自相关函数导出了不同极化状态下指数粗糙面透射波散射系数计算公式。通过数值计算得到了不同极化状态下指数粗糙面透射系数随散射角、散射方位角及入射波频率变化的曲线,讨论了粗糙面参数和入射波频率对不同极化状态透射系数的影响,得出了指数粗糙面透射系数的基本特征和随频率变化的特征。给出了一种计算二维分层介质微粗糙面双站散射系数的解析方法,将各个不同区域的波被视为无数的上行和下行波的叠加而成,这些波的振幅是由两个分界面的边界条件决定。用微扰法的公式计算了一阶散射场,这种方法考虑到了多个分界面之间的散射过程。同时利用基于电流计算的矩量法结合高频基尔霍夫近似的混合算法分析了一维指数谱粗糙地面及其上方二维无限长任意截面导体目标的复合电磁散射特性,并与传统矩量法结果进行了比较和验证。更多还原

【Abstract】 In this paper, the fundamental theory of electromagnetic scattering from the rough surfaces is introduced, different methods of electromagnetic scattering from the rough surfaces include the Kirchhoff Approximation, the Small Perturbation Approximation and the Method of Moment are discussed. Based on the comparisons between the Gaussian spectrum rough surface and Exponential spectrum rough surface, the reason of selection the Exponential spectrum rough surface as the actual land surface is given. Wang and Schmugge’s Four-elements model which shows the relation between the soil’humidity and the relative permittivity with different types of soil is introduced. Based on the Scalar Approximation and Stationary-Phase Approximation , the electromagnetic scattering in medium 2 under the rough surface is studied and formulae of the transmission coefficient for different polarization is presented with considering the autocorrelation function of the Exponential rough surface. The curve of the scattering coefficient for different polarization transmission wave with varying of the scattering angle, the scattering azimuth angle and the frequency of the incident wave is obtained by numerical implementation, the influence of the dielectric constant, rough surface parameters and the frequency of the incident wave on the transmission coefficient for different polarization transmission wave is discussed, the basic characteristics and the characteristics with varying of frequency of the transmission coefficient from Exponential rough surface is obtained. An analytical method to calculate the bistatic-scattering coefficients of a two-dimensional layered dielectric structure with slightly rough interfaces is presented. The waves in each region are represented as a superposition of an infinite number of up and down going spectral components whose amplitudes are found by simultaneously matching the boundary conditions at both interfaces. A Small Perturbation formulation is used up to the first order, and the scattered fields are derived. The calculation intrinsically takes into account multiple scattering processes between the boundaries. Meanwhile, a current based hybrid method combining the MOM with the Kirchhoff Approximation for analysis of scattering interaction between a two-dimensional infinitely long, conducting of arbitrary cross section and a one-dimensional Exponential rough surface is proposed. The numerical results give the scatterings of composite model with different size and height of target illuminated by a taper wave with different polarized wave for different incident angles. Finally, the numerical results are compared with those obtained by the conventional MOM, and the validity of our hybrid method are verified.更多还原