【作者】 王蕊；

【导师】 郭立新；

【作者基本信息】 西安电子科技大学 ， 无线电物理， 2009， 博士

【摘要】 本论文就粗糙面及其与目标的复合电磁散射中的相关问题开展了系统的理论研究工作。主要包括单层及分层随机粗糙面的电磁散射;有耗介质粗糙面与全埋、半掩埋目标的复合电磁散射;矩量法结合基尔霍夫近似的混合算法、互易性定理在粗糙面与上方目标复合电磁散射中的应用以及粗糙面与目标复合脉冲电磁散射的研究。论文主要工作如下:1.将锥形入射波引入到传统的基尔霍夫近似中,研究了考虑遮蔽效应时一、二维随机粗糙面的电磁散射问题。通过将数值结果与矩量法的结果对比发现,本文方法的计算结果与矩量法吻合较好,较传统基尔霍夫近似的计算结果更为准确。2.利用矩量法结合锥形波入射下的基尔霍夫近似研究了分层粗糙面的电磁散射。利用矩量法计算了上层粗糙面的散射场,利用基尔霍夫近似计算了从下层粗糙面进入自由空间的透射场。数值结果以高斯粗糙面为例,计算了不同极化状态下分层高斯粗糙面双站散射系数的角分布。3.推导了一维有耗介质粗糙面与半掩埋、全掩埋目标复合电磁散射系数的计算公式,并利用矩量法对其进行计算。讨论了粗糙面的均方根高度及相关长度、介质的介电常数、目标埋藏深度及大小对复合散射系数的影响。4.提出了将矩量法结合基尔霍夫近似的混合算法分析了一维随机粗糙面与上方二维无限长任意截面导体目标的复合电磁散射。混合算法将电磁散射区域分别划分为KA区域和MOM区域,其运算时间和对计算机内存的需求主要取决于目标的网格划分情况。通过与MOM结果比较表明混合算法具有较高的计算精度和计算效率,最后给出了不同极化状态下粗糙面的粗糙度、目标尺寸及高度对双站复合散射系数的影响。5.将互易性定理在两相邻目标散射中的理论扩展到求解时变介质海面与其上方运动导体平板的耦合场中。应用基尔霍夫近似求解了海面后向散射场,利用物理光学法求解了海面表面电磁流及上方导体板的散射场,同时应用互易性定理求解了海面与平板之间的耦合散射场,对后向复合电磁散射场及多普勒谱特性进行了详细讨论。6.利用时域积分方程方法计算了一维高斯导体粗糙面的瞬态电磁散射及其与上方二维无限长任意截面目标的瞬态复合电磁散射,在时域电场积分方程的基础上给出了显式及隐式MOT步进方程,数值计算并分析了复合散射模型中粗糙面中心点的电流及远场电场随时间的响应,并将计算结果与矩量法结合离散傅立叶逆变换进行了对比,验证了本文方法的有效性。最后,详细分析了入射角、目标大小及位置对电流及电场远场响应的影响。更多还原

【Abstract】 This dissertation presents the theoretical studies of electromagnetic (EM) scattering from the rough surface and the composite scattering from the rough surface with the target. Emphasis is put on studying the EM scattering from the single and layered random rough surface, the composite EM scattering from the buried and partially buried target at the rough surface, the hybrid method combining the moment of method (MOM) with the Kirchhoff approximation (KA) and the reciprocity theorem applied to the composite EM scattering from the target above the rough surface, as well as the investigation on the composite transient scattering from the rough surface and the target. The main works are as follows:1. The tapered incident wave is introduced into the classical KA to study the scattering from the 1- and 2-D randomly rough surface with the consideration of the shadowing effect. The numerical results are compared with those obtained by classical KA and MOM, which shows our results is in good agreement with those by MOM, and has a higher accuracy than the classical KA.2. MOM combining with KA considering the tapered incident wave for the analysis of the EM scattering from layered rough surface is investigated The scattered field from the upper rough surface is solved by MOM and the transmitted field from the lower rough surface into the free space is obtained by KA with neglecting the multiple scattering. The influence of the relative parameters on the bistatic scattering coefficient of Gaussian rough surface for different polarizations is discussed in detail.3. The formula for calculating the composite scattering coefficient of the buried and partially buried targets at 1-D dielectric random rough surface with lossy media is derived and solved by MOM with point matching. The effects of the root-mean-square height, the correlative length of the rough surface, the relative permittivity, the depth, as well as the size of the target on the bistatic scattering coefficient are also investigated.4. The hybrid method combining MOM with KA is proposed for the analysis of the bistatic composite EM scattering interaction between the 2-D infinitely long conducting target with arbitrary cross section and the 1-D random rough surface. The EM scattering region is divided into KA and MOM region. The computational time and memory requirements of the hybrid method mainly depend on the number of unknowns of the target. The numerical results are compared and verified with those obtained by MOM, which shows the higher accuracy and efficiency of the hybrid method than that of MOM. Finally, the influence of the surface roughness, the size and the height of the target on the bistatic scattering coefficient for different polarizations is examined.5. The reciprocity theorem used in the scattering between two adjacent targets is extended to solve the coupling field between the time-varying lossy dielectric ocean and a moving conducting plate. The backscattered field from the ocean is evaluated by the KA method. The surface electric and magnetic currents on the ocean, as well as the scattered field from the conducting plate, are evaluated by the Physical Optics method. Meanwhile, the coupling field between the ocean and the plate can be obtained by the reciprocity theorem. Finally, the characteristics and the Doppler spectrum of the composite backscattered field are discussed in detail.6. The Time-Domain-Integral-Equation method is proposed to study transient composite EM scattering from the 1-D perfect electric conducting (PEC) Gaussian rough surface and the 2-D infinitely long conducting target with an arbitrary cross section. Based on the electric field integral equation in time domain, the explicit and implicit solutions of Marching-on-Time (MOT) are presented. The current response at the center of the rough surface and the far electric field response with the time in the composite scattering model are calculated and analyzed. The numerical results are compared and verified with those obtained by conventional MOM-IDFT. Finally, the influence of the incident angle, the size and the location of the target on the current and the far electric field response is analyzed in detail.更多还原