Research On Fast Algorithm For Electromagnetic Scattering From The Random Rough Surface And The Target

With the rapid development of the technologies for radar target detection and recognition from complex background, the study on fast algorithm for electromagnetic scattering from the random rough surface and the target is of great significance. The composite scattering includes steady-state scattering and transient scattering, which should be analyzed by frequency-domain and time-domain methods, respectively. The main contributions of this dissertation are the developments of some fast frequency-domain and time-domain algorithms for the calculation of the scattering from composite model. The main works are as follows:In frequency-domain solutions for composite scattering, the hybrid method combining MOM (Moment of method) with KA (Kirchhof approximation) is given in chapter 3 for the analysis of the composite EM scattering interaction between 2-D (two-dimensional) target and 1-D PEC rough surface. The hybrid method has two kinds of representation: one is based on iteration algorithm and another based on modification of the impedance matrix. The latter is employed to calculate the scattering from the composite model with the rough sea surface. The numerical results are compared and verified with those obtained by MOM, which shows the higher efficiency of the hybrid method than that of MOM.It should be noted that the difference of the computation efficiencies of these two kinds of hybrid methods may be ignored for 1-D case, while, in chapter 4, both of them are developed to the analysis of the scattering from composite model with 2-D rough surface and a fast algorithm for the single station scattering is presented. It is found that the hybrid method based on iteration algorithm has more advantages than that based on modification of the impedance matrix. Moreover, some important conclusions are gotten by discussing the shadowing effect of the hybrid method. Hereinbefore is the fast algorithm in frequency domain, in the following, the fast algorithms in time domain are given.In chapter 5, the hybrid method which combines time domain integral equation method (TDIE) with time domain Kirchhof approximation method (TDKA) is presented for the problem of TM transient composite scattering from 1-D rough surface and 2-D conducting target. By means of applying TDKA to the rough surface while TDIE to the target and the mixed iteration of TDIE/TDKA is introduced to take accounts of the interactions between the target and the rough surface. Both explicit and implicit procedures of Marching-On-in-Time (MOT) are developed. The higher efficiency is demonstrated by the numerical results which are compared and verified with those obtained from TDIE.In chapter 6, the TDIE-TDKA hybrid method is expanded to a more complex case: TE transient composite scattering. Both explicit and implicit procedures of MOT for TE case are developed. Similarly, the higher efficiency is showed by the numerical results. Moreover, to obtain transient far scattered field, in chapter 5 and 6, a concise algorithm about near to far-zone extrapolation for TM/TE case without double Fourier transform is proposed. This algorithm is deduced directly from time-domain Green functions and is more efficient and accurate.In chapter 7, the TDIE-TDKA hybrid method is extended to the 2-D case and the explicit procedure of MOT is developed for the transient composite scattering from 2-D rough surface with 3-D conducting target. The numerical results which are compared and verified with those obtained from TDIE display higher efficiency.Finally, in consideration of that Finite Difference of Time Domain (FDTD) has a competitive advantage on solving the scattering from the inhomogeneous dielectric targets, a fast algorithm based on FDTD which combines Wavelet Galerkin Time Domain (WGTD) with parallel computing is discussed for solving the composite scattering from 1-D rough surface and target in chapter 8. Because of the smaller phase error of WGTD than that of FDTD, the grids of WGTD may be meshed larger to save computation resources. It's clear that this hybrid method has higher efficiency than FDTD from the comparison of their numerical results.The work of this dissertation provides a set of fast and efficient theoretical algorithm for the numerical simulation of the composite scattering from the target and randomly rough surface in both frequency and time domain.