Guided electromagnetic waves in a periodically nonuniform tunnel

A boundary value analysis is outlined for the transmission in a circular tunnel that contains a thin axial conductor. The series impedance of the latter is allowed to vary in a periodic fashion throughout its length. Simplifications of the formal mode equation are achieved by invoking quasi-static conditions used in previous studies. It is shown that the axial nonuniformity can be represented approximately as a modification of the series impedance of the equivalent transmission line of the composite tunnel structure.