On the application of the GTD-MM technique and its limitations

In 1975 two techniques were published that combined the method of moments (MM) and the geometrical theory of diffraction (GTD). One technique extended the moment method through the use of the GTD while the second used the moment method to solve for unknown diffraction coefficients, thereby extending the use of the GTD. It is the latter method that is considered in this paper and is referred to as the GTD-MM technique. One problem area that existed with the original GTD-MM work was associated with a field incident along or nearly along one wall of a wedge structure. An improved series representation for the diffracted current that is sufficient at all incidence angles is shown. The improved formulation is then applied to the problem of bistatic scattering by a three-sided pyramid. Radar cross section (RCS) results that compare very well with experimental measurements are obtained. This is believed to be the first use of the GTD-MM technique in treating a three-dimensional geometry.