Numerical computation of diffraction coefficients

Direct numerical methods are explored for the computation of diffraction coefficients for a wide class of canonical structures. Although these canonical structures are infinite or semi-infinite, the initial computations are performed on finite bodies. Extraction of the desired coefficient therefore necessitates the elimination of radiation from extraneous diffraction centers. This is accomplished by a variety of techniques including current windowing, tapered resistivity, and screening by conducting shields. Singularities at shadow boundaries are derived via physical optics (PO). The procedure is elucidated through a number of examples for which analytic results are available for comparison. These include the perfectly conducting half-plane, wedge, rounded wedge, and grooves in a ground plane. Computed diffraction coefficients for lossy dielectric wedges are applied within the context of geometrical theory of diffraction (GTD) to the computation of diffraction from a triangular prism and the results are in satisfactory agreement with those of the method of moments (MM).