Numerical diffraction coefficients in the shadow transition region

Numerical techniques for the evaluation of diffraction coefficients are extended to shadow transition regions and examined in detail for perfectly conducting and lossy dielectric semi-infinite slabs with a line source in the near-field and polarization along the slab edge. One approach is based on a direct computation of the radiation from a finite two-dimensional slab illuminated from a near-field source, with the current filtered by appropriate windows. For the perfectly conducting half-plane this approach yields diffraction coefficients in the transition region that are in good agreement with uniform theory of diffraction (UTD) analytic values. Alternatively, geometric theory of diffraction (GTD) coefficients are computed once and for all for a far-field source and these are used formally within a UTD or uniform asymptotic theory (UAT) framework. The direct, the UTD, and the UAT approaches are in satisfactory agreement with each other, and predictions for the radiation from finite slabs based on the computed diffraction coefficients are in satisfactory agreement with those of the method of moments (MM).>