Circuit-Modeling approach for broadband analysis of non-uniform transmission lines including radiation

A novel inherently passive and convergence accelerated Foster-type circuit model for non-uniform, radiating transmission lines (TLs) is presented. The straightforward derivation is based on the solution of TL equations by an eigenvector expansion. Modal conductances consider radiation losses, calculated from the radiated power of modal far fields. So far not found in the literature, the definition of the per-unit-length parameters for nonuniform TLs is reviewed and an accurate general expression is developed. The accuracy of the suggested SPICE compatible network model is demonstrated by a comparison with a more elaborate full-wave simulation in time domain, including non-linear terminations.