Narrow-waisted Gaussian beams for aperture-generated scattering from planar conducting surfaces with complex coatings described by higher order impedance boundary conditions

In this paper, we use higher order impedance boundary conditions (HOIBCs) for studying high frequency asymptotic two-dimensional (2-D) scattering of truncated aperture-generated electromagnetic fields from planar conducting surfaces coated by multiple layers of homogeneous bi-anisotropic media. The reflected field syntheses are carried out via asymptotic reduction of rigorous plane-wave spectral integrals, which are subsequently discretized and transformed to the spatial domain through use of a Gabor-based narrow-waisted (NW) Gaussian beam (GB) algorithm. In this discretized algorithm, the GB propagators are approximated by previously explored standard and modified (uniform) complex-source-point paraxial asymptotic techniques. Example applications are restricted to zeroth and second order IBCs for single- and multilayer complex coatings, with emphasis on the adaptation of the NW-GBs to the HOIBC launch conditions in the presence of localizing (e.g., focused and/or abruptly truncated) illumination. The results confirm that the previously established utility of the NW-GB algorithm with respect to accuracy and computational feasibility continues to hold for this fairly general combination of environmental complexity and strongly inhomogeneous (localizing) illumination.