Computation of the scattering by planar and nonplanar plates using a conjugate gradient FFT method.

Abstract

It is well known that sharp edges and corners of objects illuminated by electromagnetic radiation produce a significant secondary radiation. Unfortunately, very little is known about the mechanisms producing this phenomenon. To achieve a better underst and ing, it is therefore desirable to mathematically model the scattering characteristics of the simplest scatterer having both corners and edges. Such a model should, of course be amenable to analysis. The major goal of this study is to develop an efficient conjugate gradient FFT method to numerically solve for the induced current and scattered field of a material plate illuminated by an E or H polarized plane wave. Achieving an efficient algorithm requires a good underst and ing of both the conjugate gradient method and the computation of the FFT. A complete derivation of a conjugate gradient method and the FFT is given in the text. There are two basic plate configurations of interest in this study. The first is the single material plate, which includes the zero thickness perfectly conducting plate, the electrically thin dielectric plate and the combination dielectric and magnetic plate. The second is the dielectric coated or combination dielectric and magnetic coated perfectly conducting plate. Computed results for surface currents and the radar cross section are given. In this thesis, a new hybrid method is proposed that combines a boundary integral method with a conjugate gradient FFT method to solve for the scattering from an object having arbitrary geometry and material composition. A synthesis algorithm for determining the material distribution of a plate yielding a certain scattering characteristic is also proposed.