Complex propagation coefficients and the step discontinuity in corrugated cylindrical waveguide

The letter is concerned with the nature of evanescent modes in circumferentially corrugated cylindrical waveguide. When the longitudinal surface susceptance is small, the propagation coefficients for these modes must become complex. A knowledge of evanescent modes is necessary when discussing discontinuities in waveguides; some preliminary results for a modal analysis of the step-discontinuity problem in corrugated waveguide are presented.