Application of the conjugate gradient FFT method to large radiating systems using subdomain basis functions

A technique is presented to improve the convergence of the conjugate-gradient fast Fourier transforms (CGFFT) method by the incorporation of subdomain basis functions associated with linear and planar radiating elements. To this end, the current is expressed as a convolution of a pulse basis with a finite sequence of delta functions whose amplitudes are the sampled values of the current. Using this current representation and the convolution theorem, the CGFFT formulation is extended to general basis functions. It is shown that significant improvements are achieved in the convergence of the method using sinusoidal basis functions. The improvement in the convergence is attributed to a more accurate approximation of the antenna current distribution.<>