Nonuniform transmission-line structures: internal and external propagation parameters

A discussion on the relationship between the internal and external propagation parameters of a simple two-conductor nonuniform transmission line is presented. The analysis, developed in the framework of the quasi-transverse electromagnetic (TEM) approach, is aimed at the clarification of the concepts underlying the definition of those parameters, propagation constants and characteristic wave impedances. It is shown how the two different viewpoints (internal and external approach) come to agree, despite their apparent conflict. A numerical application concerning a typical microwave impedance-matching device made of an exponential-line section is provided for exemplification purposes.