An improved FB/NSA algorithm for the computation of scattering from two-dimensional large-scale rough surfaces

The forward-backward method with a novel spectral acceleration algorithm (F B/NSA) has been shown to be a very efficient O(N-tot) iterative method of m oments, where N-tot is the total number of unknowns to be solved, for the c omputation of electromagnetic wave scattering from two-dimensional (2-D) ro ugh surfaces (3-D scattering problems). For relatively large surface cross- range sizes Dy the method's efficiency decreases due to the increase of the direct computation of the mutual coupling in the strong region. An additio nal NSA formulation based on spectral domain representation of the Green's function in the cross-range direction is incorporated into the standard NSA algorithm to improve its computational efficiency. In addition, for the ca se of extremely large-scale rough surfaces, a "multilevel" algorithm (i.e., decomposing 2-D extremely large-scale surfaces into more than one weak reg ion and appropriately choosing the NSA parameters for each weak region) is incorporated into the standard FB/NSA algorithm to improve its accuracy. It is found that the improved FB/NSA algorithm remains O(N-tot). Numerical re sults show that the efficiency and accuracy of the standard FB/NSA algorith m are improved by incorporating the y-expansion and the "multilevel" algori thm at the cost of increasing algorithmic complexity and memory requirement s.