A theoretical study of propagation along tape ladder lines

Dispersion curves are calculated for single-ridge, double-ridge, single T-section and double T-section ladder lines in which the rungs of the ladder are thin tapes. Each structure is broken up into several regions having simple geometries. In each region the electromagnetic field is expanded as a series of suitable wave functions. Matching of the fields at the boundaries of the regions leads to an infinite set of homogeneous linear equations for the coefficients in the expansions. These equations have a non-trivial solution only if the determinant of their matrix is zero. The dispersion curves are obtained numerically from such determinantal equations. They confirm the qualitative predictions. Throughout the analysis, the ladder is approximated by a uniform sheet which conducts only in the direction of the tapes.