【作者】 余定峰；

【导师】 朱国强；

【作者基本信息】 武汉大学 ， 无线电物理， 2013， 博士

【摘要】 目标雷达散射截面(RCS)的缩减在军事领域具有重要的意义,是雷达对抗中的关键技术之一。将具有雷达吸波特性的介质薄层涂覆于导体目标外表面,以削弱目标散射电磁波的能量,并使电磁波尽可能地朝着无关的方向散射,这已成为复杂目标电磁隐身技术所追求的目标。介质薄层涂覆导体目标电磁散射问题是计算电磁学领域具有实际应用价值的课题,在雷达目标探测、电波传播以及高频天线设计等领域有着广泛的应用,同时也成为雷达反隐身领域所关心的研究课题,在电子对抗中有着广阔的应用前景。通过阻抗边界条件(IBC)将介质薄层涂覆导体目标等效为无厚度阻抗面,采用表面阻抗并矢给出切向电场和磁场矢量之间的关系,无需考察物体内部场分布便可计算物体外部散射场,避开了介质与导体复合目标中格林函数的推导和计算等难点问题,可将未知量限制在整个涂覆导体的外表面,便于采用表面电磁场积分公式实现电磁散射特性的高效求解,从而简化复杂结构电磁散射问题的分析和数值求解过程。本文基于阻抗边界条件,研究了介质涂覆不同电尺寸目标电磁散射算法及特性仿真。针对电小尺寸目标,提出了无限长任意形状截面非均匀各向异性阻抗柱面和介质涂覆三维导电目标电磁散射的矩量法(MoM),对于矩量法精确积分计算目标表面所有三角形面元之间的相互作用而效率低的问题,采用矢量多层UV分解技术,减少迭代求解矩阵方程时的矩阵-向量积运算,减少计算机内存需求和计算时间,从而有效提高计算效率,拓宽其应用范围；针对电大尺寸目标,将其电磁散射贡献划分为占主要地位的面散射贡献和占次要地位的边缘绕射贡献。采用双次反弹的物理光学(PO)算法求解面散射贡献,并通过任意斜入射情况下任意劈角阻抗直劈的一致性几何绕射理论(UTD)解导出有限长阻抗直劈边缘的增量长度绕射系数(ILDC)或等效边缘流(EEC),从而以边缘波场修正物理光学场,得到介质涂覆电大尺寸三维导电目标电磁散射的高频预估；针对介质涂覆中等电尺寸目标,提出了矩量法-物理光学(MoM-PO)混合算法解决方案。此外,基于本文提出的各类电磁散射理论算法,进行了地／海环境中目标的电磁散射特性预估及雷达成像仿真研究,对目标特性理论研究和雷达系统改善提供理论指导与数据支撑。本文内容主要包括：1)研究了介质涂覆电小目标电磁散射的MoM算法建模。包括无限长任意形状截面非均匀各向异性阻抗柱面电磁散射的MoM算法,介质涂覆三维导电目标电磁散射的MoM算法,以及矢量多层UV分解技术加速的介质涂覆导电目标电磁散射的MoM算法。2)研究了介质涂覆电大目标电磁散射的高频算法建模。包括阻抗平面电磁散射的双次反弹物理光学算法,以及有限长阻抗直劈蜡边缘绕射的增量长度绕射系数算法3)研究了介质涂覆中等电尺寸目标电磁散射的MoM-PO混合算法建模。将散射体上的边、角等不连续区域划归MoM区,而把其它光滑、连续的区域划归PO区,对于曲率无明显变化的目标,则可以将散射贡献较大的少量区域划归MoM区,则空间散射电磁场可等效为MoM区和PO区电磁流的辐射场。4)研究了地/海环境中目标的高频电磁散射特性及雷达成像仿真。采用基于双次反弹的PO-EEC算法实现目标与地/海环境复合散射的一体化高精度电磁建模,仿真得到地/海环境中目标的单站RCS以及高分辨率距离像(HRRP)/二维聚束合成孔径雷达(SAR)成像特性。更多还原

【Abstract】 As one of the key techniques in radar counterwork, the radar cross section (RCS) reduction is of great significance in military fields. Coating the outer surface of conducting target with radar absorbing thin-layer dielectric, can not only weaken the electromagnetic energy scattering from the target, but also redistribute the scattering electromagnetic waves to the uncaring direction, which has become a pursued goal in electromagnetic stealth field for complex target. The research on the electromagnetic scattering of conducting target coated with thin-layer dielectric, as a topic of great value in computational electromagnetics, has a wide range of applications in the fields of radar detection, electromagnetic wave propagation, as well as high-frequency antenna design, and become of great concern in the field of radar anti-stealth, which has broad application prospects in electronic countermeasures. Conducting object coated with thin-layer dielectric is equivalent to impedance surfaces with no thickness using impedance boundary condition, with the relationship between tangential electric field and magnetic field vectors given by a surface impedance dyadic. The external electromagnetic field scattered from the thin-layer dielectric coating object can be calculated with no need to investigate the distribution of the internal field, which can avoid some difficult problems such as the derivation and calculation of the Green’s function for the composite target. Furthermore, the unknowns can be greatly limited to the outer surface of the coated conductor, and then surface electromagnetic fields integral formulas can be used to efficiently explore the electromagnetic scattering, thus simplifying the procedure of analysis and numerical solving for electromagnetic scattering from complex structures.The research on electromagnetic scattering algorithms and characteristics simulation for thin-layer dielectric coating object of different electrical size, based on the impedance boundary condition is performed in this paper. For the case of small electrical size, method of moments(MoM) is presented respectively for the electromagnetic scattering from two-dimensional anisotropic inhomogeneous impedance cylinder of arbitrary section shape and three-dimensional arbitrary conducting object coated with dielectric. Exact integration to calculate the interaction between surface triangular facets is needed in three-dimensional MoM solution, which may result in low efficiency. Multi-layer UV decomposition technique is adopted to reduce the computer memory requirements and computation time by reducing the complexity of the matrix-vector multiplication in iterative solution, in order to effectively improve the computational efficiency and broaden its range of application; For the case of large electrical size, the total electromagnetic scattering is divided into the dominant contribution of surface scattering and the secondary contribution of edge diffraction. The double-bounce physical optics (PO) algorithm is applied to obtain the surface scattering contribution. With the help of uniform geometrical theory of diffraction (UTD) solution by impedance wedge with arbitrary exterior wedge angle at arbitrary skew incidence, the incremental length diffraction coefficients (ILDC) or equivalent edge current (EEC) for finite edge can be derived, in order to improve the physical optics field with fringe wave contribution, to implement the high-frequency estimation of electromagnetic scattering from electrically large conducting object coated with dielectric; For the case of dielectric coating conducting target of medium electrical size, a MoM-PO hybrid method is presented for the electromagnetic scattering. In addition, the electromagnetic scattering and radar image of ground/maritime targets are performed based on the proposed various algorithms, which may provide theoretical guidance and database support, to improve the theoretical research for target characteristics and radar systems. The main content of this paper includes the following parts:1) The electromagnetic scattering from electrically small conducting object coated with dielectric is studied by the MoM algorithm, respectively for the scattering from two-dimensional anisotropic inhomogeneous impedance cylinder of arbitrary section shape and three-dimensional arbitrary conducting object coated with dielectric. Multi-layer UV decomposition technique is adopted to accelerate the MoM algorithm for conducting object coated with dielectric.2) The electromagnetic scattering from electrically large conducting object coated with dielectric is studied by the high frequency algorithm, including the double-bounce PO method for impedance surface, as well as the ILDC for finite impedance edge.3) The electromagnetic scattering from electrically medium conducting object coated with dielectric is studied by the MoM-PO hybrid method. The discontinuous, geometrically complicated parts or the part with a rapid change in curvature, such as edges or corners will be grouped into the MoM-region generally, while the left continuous, smooth parts will be grouped into the PO-region. Then the total scattering fields can be equivalent to the radiation of electric or magnetic current in the MoM-and the PO-region.4) The high frequency scattering characteristic and radar image of ground/maritime targets are studied. The electromagnetic simulation of composite scattering from targets and the land/sea environment are performed by the PO-EEC algorithm, in order to obtain the RCS, high resolution range profiles (HRRP) and2-D spotlight synthetic aperture radar (SAR) image.更多还原