Fast computation of RCS from electrically large 3-D homogeneous objects

Based on the combined tangential formulation (CTF) of surface integral equation, the lower triangular approximate Schur preconditioner (LTASP) is combined with multilevel fast multipole algorithm (MLFMA) for MoM analysis of electromagnetic scattering from electrically large 3-D homogeneous objects. The coefficient matrix of the near-field coupling element was selected to set up the approximate matrix, and both sparse approximate inverse (SAI) and dual threshold incomplete LU factorization (ILUT) are used for constructing the preconditioner to accelerate the convergence of GMRES iteration. Numerical examples are presented to demonstrate the performance of the proposed preconditioner. A scattering problem of dielectric sphere with the diameter of 40 wavelengths and dielectric constant of 4.0 has been solved successfully.