| Approximate and relatively simple but closed form Uniform Geometrical Theory of Diffraction (UTD) solutions are obtained for describing the radiated, scattered and surface wave fields, respectively, excited by sources near or on a canonical geometry consisting of a thin, planar, three-dimensional (3-D) double positive/double negative (DPS/DNG) material coated metallic wedge with an arbitrary wedge angle. Thus, unlike previous works that consider primarily plane wave scattering by such DPS structures via the Wiener-Hopf (W-H) or Maliuzhinets (MZ) methods, the present development can also treat radiation and coupling problems of antennas near or on nite material coated metallic surfaces. The latter is made possible mainly through the introduction of higher order UTD slope diffraction terms added to first order UTD. It is noted that all previous solutions based on rigorous W-H and MZ formulations employ approximate boundary conditions; in contrast, the present solutions, which are developed via a heuristic spectral synthesis approach, recover the proper local plane wave Fresnel reflection and transmission coefficients and surface wave constants of the DPS/DNG material. They also include the presence of backward surface waves in DNG media. Besides being asymptotic solutions of the wave equation, the present UTD diffracted fields satisfy reciprocity to first order UTD, the radiation condition, boundary conditions on the conductor, and the Karp-Karal lemma which dictates that the first order UTD space waves vanish on a material interface. |
