In this thesis a numerical technique to model general microstrip asymmetric and multiple step discontinuities is presented. The method is based on a magnetic wall waveguide model that is assumed to be valid for describing the electromagnetic fields associated with the microstrip line and in the vicinity of microstrip discontinuities. The fields are expanded in the uniform regions and the mode-matching method is applied at the discontinuities to analyze for the frequency dependent transmission properties of the multi ports. The generalized scattering matrix technique is used to model cascaded interacting discontinuities and is used to compute the properties of double-step and multi port structures. The generalized scattering matrix formulation takes into account the scattering phenomena of the dominant and all of the higher-order modes including evanescent ones. The validity of this model has been discussed extensively, and it is shown that the model can be used to describe the microstrip discontinuities with acceptable accuracy. The technique is applied (1) to study the transmission characteristics of asymmetric step discontinuities; (2) to design a filter for a desired frequency range using interacting asymmetric double step micros trip line; and (3) to design a new nominal 3db power devider of large bandwidth consisting of a three port rectangular patch. The techniques and models presented can be used in computer-aided analysis and design of such circuits
