S-parameter characterization of nonuniform microstrip lines via perturbative technique

This paper presents a frequency-domain perturbative technique for the solution of nonuniform transmission-lines (NUTLs), resorting to a preliminary S-parameter characterization. According to this method, the NUTL S-parameter matrix is obtained column-by-column, by solution of NUTL subproblems involving different terminal networks. The procedure results to be particularly suitable in the case of differential lines with fully or partially repetitive geometry, since it allows good prediction accuracy and reduced computational burden. As explicative examples, the technique is here applied to high-speed microstrip line configurations for common-mode suppression.