RCS calculation for large inhomogeneous penetrable objects using a spectral integral equation solver

We attempt to solve large scale scattering problems of inhomogeneous bodies by solving a volume integral equation. We develop a spectral method using the FFT in the weak-form discretization of the integral equation. This spectral method requires O(Nlog/sub 2/N) CPU time and O(N) computer memory, where N is the number of unknowns. It converges several times faster than previous methods. With this spectral method, we are able to solve a large problem with over 12.7 million unknowns. We have validated our numerical results by comparing with Mie series for a multilayer spherical medium. The method has been used to model a large penetrable missile-like object.