Resistive treatment of edges in MLFMA LGA scattering from finite conductivity 2D surfaces

Several approaches have been used to reduce or eliminate the effects of artificial surface-truncation edges on the numerically calculated scattering from rough surfaces. Some approaches become quite expensive at low grazing angles (LGA). We consider the suppression of edge effects using resistive loading in the numerical scattering from two-dimensionally rough surfaces. The multi-level fast multipole approach (MLFMA) (see Song, J.M. and Chew, W.C., Microwave and Optical Technology Letters, vol.10, no.1, p.14-19, 1995) is applied to two-dimensional surfaces that approximate breaking water waves. Two different resistive-loading schemes are considered. In the first, the loading is applied only to the front and back edges (in range) of the wave, and the azimuthal edges are suppressed using a Gaussian illumination window. In the second, the resistive loading is applied to both the range and azimuthal edges. In both cases, where applicable, the results are verified through a comparison with the results of the 1D MM/GTD approach (see West, J.C., IEEE Trans. on GRS, vol.38, no.4, p.1609-16, 2000).