A new generalized modal analysis theory for nonuniform multiconductor transmission lines

Modal analysis theory plays a key role in the study of multiconductor transmission-line structures. Yet, with a few exceptions, the scope of application of the modal theory has been mainly focused on uniform line structures. However, in a very recent work by Semlyen, a new development suited for the analysis of nonuniform line structures has been presented. Such a work triggered the present paper, where a complementary generalized theory based on ABCD matrix analysis is developed encompassing both uniform and nonuniform transmission lines. A detailed study, using matrix methods, is presented, showing how modal decoupling of transmission line equations can be achieved in the general case of multiconductor nonuniform structures. Appropriate coordinate transformations are introduced. Wave propagation parameters (modal propagation constants and forward- and backward-modal surge admittances) are defined.