Research On Fast Methods For Rough Surface Scattering And Its Composite Scattering With Target

Many fields in modern science and technology cannot get away from the scattering of electromagnetic waves, such as non-destructive detection, communication, radar navigation, stealth technology, seismic exploration and remote sensing. Research on rough surface electromagnetic scattering has significant academic value and broad application prospects in the national defense and military fields and civilian technology. Periodic surface as a very important optical reflection rough surface, it has been widely used in the frequency scanning reflector, coupler, polarizer and band-pass filter, etc. When detecting target in a complex background, it is necessary to simulate the complex background as random rough surface and carry out the research on the composite scattering from the target above the rough surface, to properly consider the terrain or sea clutter. This paper studies fast method of two type of scattering problems related to the rough surface scattering:periodic surface scattering and the composite scattering of target above rough surface. For the first type problem, we propose a transform method to calculate the scattering from dielectric periodic surface whose surface corrugation is not deep. Then the complex image method is proposed to accelerate the calculation of periodic Green’s function, which is kernel of integral equation used in method of moment (MoM). For the second type problem, we propose the hybrid method which combines the analytic Kirchhoff approximation (KA) and numerical MoM. This method is of high efficiency, and as its less limitations, it has more general applicability. The main works are as follows:1. The extended transform method is developed for calculating the2-D scattering problem from dielectric periodic interfaces. The method transforms the problem into scattering from two imaginary planes, one of which cuts across the maximum points and another across the minimum points of the periodic interface. Compared with other methods, this method is a high efficient and simple method to solve the scattering field in the trough region of the corrugation, but it can not get accurate result with periodic surface whose surface corrugation is deep.2. One-level complex image method to derive closed form periodic Green’s function for problem of scattering from perfectly conducting periodic surfaces, is considered. Then the integral equation with the complex images periodic Green’s function in the kernel is solved by the method of moments. However as the frequency increases, this one-level complex image method has difficult to find an adequate approximation parameter. So the two-level complex image method is derived to provide compensation for the contribution neglected in the previous one-level approach.3. The current based hybrid method combining analytic KA and numerical MoM is developed to solve the two-dimensional (2D) scattering problem of a dielectric target with arbitrary cross section above a conducting/dieletric rough surface under TE-polarize and TM-polarized tapered incident. The KA is used for the calculation of the Gaussian rough surface and MoM for the target, and the integral equations of the induced electric and magnetic currents on the target only can be derived, so the problem depends mainly on the number of unknown of the target. Based on the local specular reflection of the rough surface, the rough surface can be truncated to speed up computation of the scattering contribution from the rough surface to the target.4. The current based hybrid method is generalized for multiple targets above a conducting rough surface under TE-polarized tapered incident. Taking two cylindrical targets above a PEC rough surface as an example, the coupling effect between two targets with different horizontal distance is analized.