Accelerated Hybrid Method for Electromagnetic Scattering From Multiple Complex Targets Above a Rough Surface

A hybrid scheme that combines the pre-corrected fast Fourier transform (p-FFT) and iterative Kirchhoff approximation (IKA) is developed to solve the electromagnetic scattering from multiple complex targets above a three-dimensional (3D) rough surface. Based on the domain distribution method (DDM), multiple targets are divided into an FFT region, and the rough surface is divided into an IKA region. Scattering on the FFT region and IKA region is calculated by p-FFT and IKA, respectively. In addition, iterative strategies are considered in both solving interaction between facets in the IKA region and interactions between FFT region and IKA region. However, interactions between FFT region and IKA region are the most time-consuming in the entire computational process. To overcome this computational bottleneck, the combined multilevel fast multipole algorithm (MLFMA), ray-propagation fast multipole algorithm (RPFMA) and fast far-field approximation (FAFFA) are incorporated into interactions between FFT region and IKA region. They accelerate the matrix vector multiplication by "interpolation -translation -anterpolation", while their translators are different, which result in their different computation efficiencies and application conditions. To effectively combine these three algorithms, the IKA region is divided into MLFMA area, RPFMA area and FAFFA area according to the distance, where interactions between these areas and the targets are accelerated by MLFMA, RPFMA and FAFFA, and the surface outside these areas is discarded. Compared with MLFMA, the accuracy and efficiency of this hybrid method are verified.