Improving the convergence rate of the conjugate gradient FFT method using subdomain basis functions

A technique to improve the convergence rate of the conjugate gradient-fast Fourier transform (CG-FFT) method is presented. The procedure involves the incorporation of subdomain basis functions associated with the current representation of linear and planar radiating elements. It is shown that significant improvements are achieved in the convergence of the CG-FFT when using sinusoidal basis functions. Numerical results are presented for thin cylindrical dipoles, conducting strips, and material plates of various sizes. In all cases, an increase in the rate of convergence by a factor of two or better was observed