Rigorous Computation of the Frequency Dependant Properties of Filters and Coupled Resonators Composed from Transverse Microstrip Discontinuities

A numerically efficient method is presented, which yields the propagation constants and the field distributions of basic and higher order modes of shielded microstrip lines. Upon this basic a mode matching technique is applied in order to calculate the frequency dependant generalized scattering matrices of transverse microstrip discontinuities like impedance steps and open ends. From these discontinuities several microstrip components like filters, transverse gaps, and coupled resonators can be composed. Important effects like convergence behaviour, numerical stability, and the influence of higher order propagating and not propagating modes have been studied, and some interesting numerical and experimental results are presented.