Modeling discontinuities in dielectric-loaded waveguides

The mode-matching technique is applied to model step discontinuities in dielectric-loaded cylindrical waveguides excited by hybrid modes. It is shown that the field solution obtained by mode matching does not converge unless complex modes are included in the field expansion. If the structure parameters and operating frequency allow for the existence of complex modes, then the purely propagating and evanescent mode fields do not form a complete set unless complemented by the complex mode field. Numerical results that clearly illustrate the role of the complex mode fields in the modeling of step discontinuities are presented. Examples illustrating the representation of the step discontinuities by a multiport scattering matrix are included.<>