Resistive suppression of edge effects in MLFMA scattering from finite conductivity surfaces

The use of resistive loading to suppress edge-diffraction effects in three-dimensional numerical multilevel fast multipole algorithm calculation of scattering from arbitrary rough surfaces has been considered. The effectiveness of the loading is similar to that obtained in earlier work using a two-dimensional moment method applied to surfaces that are infinitely uniform in the azimuthal direction. The loading dramatically reduces the direct back-diffraction from the edges. However, current perturbations induced by the loading can introduce significant errors if the local angle of incidence on the leading-edge loaded area exceeds approximately 70°. The loading is effective with finite conductivity surfaces modeled using impedance boundary conditions. The method is particularly suitable for use at high incidence (low grazing) with surfaces where the leading and trailing edges on which the loading is applied may be naturally angled downward from horizontal without affecting the scattering.