FDTD Method Application On The Problem Of Half-space Scattering

This dissertation gives the Finite Difference Time Domain (FDTD) method theory in EM scattering problem, including the difference iteration formulas, the stability condition, the absorbing boundary, the total field/scattering field (TF/SF) boundary, as well as the near-to-far field transformation boundary. Some corresponding examples are also presented to obtain the near field visualized results and RCS of far field, which show the accuracy of the FDTD algorithms.The works of this dissertation are as follows:The scattering of simple target in free space is calculated using the FDTD method, including two-dimensional (2-D) and three-dimensional (3-D) time-harmonic wave excitation case, and the results are compared with corresponding literature, which are in good agreement.The scattering by a simple target is analyzed by using the FDTD method as a half-space problem. The driving waves are composed of the incident wave, reflected wave and transmitted wave. The incident and reflected waves propagate in the upper medium (usually free-space), while the transmitted wave propagates inside the lower medium (usually dielectric). And the result of the far-zone scattered field of the target is aquired by the near-field to far-field extrapolation formulas in half-space.By using Monte Carlo method to simulate one-dimensional random rough (sea) surface, and the electromagnetic scattering with the time harmonic incident wave by 1D rough surface with/without target is calculated by using the FDTD method. The influence of the root-mean-square (rms) height, the correlation length, the relative dielectric constant, and the electrical conductivity of the rough surface on the scattering of 1D rough surface with/without a 2D target is discussed. The targets including simple circle, missile above 1D Gaussian rough surface, ship on the sea surface, where we use a PM surface roughness spectrum to generate the rough sea surface.By using Monte Carlo method to simulate two-dimensional Gaussian rough surface, and the electromagnetic scattering with the time harmonic incident wave by 2D rough surface is calculated by using the FDTD method. Besides, the problem of dispersive half-space scattering is simply studied.Half-space problems in the study are given in two ways: we use a composite driving wave comprising three components—the incident, reflected, and transmitted waves for a plane half-space. While for rough surface, it is truncated in the FDTD simulation, we use Gaussian window function to eliminate the influence.