Closed-form description of coupled microstrip line step discontinuities

Symmetric coupled microstrip line step discontinuities are analyzed and modeled. Equivalent even and odd mode networks taking into account fringing field and current distribution effects are derived for the junction. A comprehensive four port description of the even and odd mode lumped components is set up. For a given substrate and frequency closed-form expressions are derived by curve-fitting data sets obtained from a systematic full-wave parameter study of a class of discontinuities.