Abstract
In this letter, we present a technique for an efficient evaluation of the reduced matrix in the context of the characteristic basis function method (CBFM) for the simulation of microstrip circuits printed on layered media. The underlying concept is to evaluate the off-diagonal terms of the reduced matrix, which vary much less rapidly then the diagonal ones, in the spectral domain, while the self-interactions are computed in the conventional way. Numerical examples are presented to demonstrate that the fill-time of the reduced matrix is reduced by working in the spectral domain, as compared to the spatial domain evaluation in the conventional CBFM, while maintaining the computational accuracy of the results. Furthermore, the efficiency of the present approach increases rapidly as the number of unknowns in each block is increased.