Numerical Analysis of Electromagnetic Scattering from Three Dimensional Objects with Arbitrary Shape and Its Experimsents

采用等效偶极子方法研究了任意形状三维物体的电磁散射问题，该方法将散射场近似为假设的多重偶极子产生的场。首先研究了具有旋转对称的完全导电和有限长度介质圆柱体作为散射体的例子，并与其他方法的结果和X波段的实验结果进行了比较，研究了它们的边缘对雷达截面和散射场的影响。结果表明，对于完全导电圆柱体，无论散射体是否有边缘，本文方法都能准确计算出前后散射截面，而边缘的存在对散射场图形的数值精度影响较大。另一方面，对于介质圆柱体，即使散射体有边缘，也能精确地计算出散射体的散射系数。在此基础上，结合等效偶极子方法提出了两种有效的方法，分别适用于直径较大的散射体和直径较小的散射体。前者是基于对称坐标的多相照明方法，后者是将细长散射体的中心区域作为二维结构的部分二维方法。特别是后一种方法成功地应用于有限长、有限直径细线天线的分析。由此可见，当天线直径或馈电间隙大于波长的百分之一数量级时，会影响半波长天线的特性。最后，以具有任意形状的三维物体为例，研究了包含多个奇异边和角的完美导电立方体。雷达截面的数值计算结果与实验结果吻合较好，从而证实了等效偶极子方法对三维散射问题的分析是非常有用的。少

The electromagnetic scattering problems from three dimensional objects with arbitrary shape were investigated by the equivalent dipole method, which approximates the scattering fields in terms of the fields generated by the hypothetical multiple dipoles. The perfectly conducting and the dielectric cylinders of finite length with rotational symmerty were first examined as an example scatterer, and their edge effects on the radar cross sections and the scattering fields were investigated in comparison with the results obtained by other method and also with experiments in the X band. As a result, it was found that for the perfectly conducting cylinder, the forward and backward radar cross sections could be accurately calculated by the present method whether the scatterer may or may not have edges, whereas the numerical precision of the scattering field patterns were much affected by the existence of an edge. On the other hand, those for the dielectric cylinder were accurately calculated e … More ven if the scatterer has an edge.Next, we proposed the two efficient approaches incorporated with the equivalent dipole method, which were useful for a scatterer with large diameter and for a slender one respectively. The former is the multiphase-illumination approach based on the symmetric coordinates and the latter is the partially two-dimensional approach which regards the central region of a slender scatterer as the two-dimensional structure. Especially, the latter approach was successfully applied to the analysis of the thin wire antennas with finite length and finite diameter. Then it was clear that the characteristics of the half-wavelength antenna are affected when the diamiter or the feeding gap interval becomes larger than the order of a hundredth of the wavelength.Finally, as an example of the 3D object with arbitrary shape, the perfectly conducting cube including many singular edges and corners was investigated. The numerical results of the radar cross section showed good agreement with the experimental ones and so it was confirmed that the equivalent dipole method was very useful for analyzing the 3D scattering problems. Less