Efficient high-frequency techniques for scattering by realistic targets

Abstract

A significant problem in electromagnetics is the computation of the scattered far fields for large, complex targets, such as tanks or aircraft. Since it is often necessary to determine the scattering at multiple angles and frequencies, speed of calculation can be critical as well. This work has direct applications in areas such as RCS reduction and target identification, with the latter being the main thrust of this thesis. In order to do these computations, high-frequency approximate techniques must be used.

It has been found that computer graphics rendering techniques can be used to significantly improve the time necessary to achieve very good high-frequency first-bounce scattering results for an arbitrarily complex target. This is done using an area of memory known at the z-buffer.

An improvement over our previous implementations of shooting and bouncing rays is also presented. For the case of a ray at grazing incidence on the surface of a target, unrealistic results were predicted. By adding a "shape function", which accounts for the phase variation over the projected raytube surface, better results can be determined.

In an attempt to handle a more general problem, a shooting and bouncing rays solution to the bulk material case is presented, for both lossless and lossy materials. This includes problems containing bulk materials alone, and problems integrating various other materials, such as conductors. Previously, only surfaces with thin layers of material have been implemented, using a simple reflection coefficient. A number of different cases are presented and are compared to results obtained using a two-dimensional method of moments code. It is found that good accuracy can be obtained for many cases.