Full-wave analysis of discontinuities in planar waveguides by the method of lines using a source approach

An accurate full-wave analysis of discontinuities in shielded microwave structures by the method of lines is presented for use in microwave integrated circuit design. The input currents are derived from a sinusoidal source representation and modeled by inhomogeneous boundary conditions. Interacting discontinuities can be treated without segmentation. Inhomogeneous boundary conditions are introduced to account for the excitation. Analysis shows that in discretizing the differential operators additional source terms which result in inhomogeneous differential equations are obtained. A deterministic equation for the current distribution is derived. For higher flexibility, nonequidistant discretization is used. The scattering parameters are presented for the microstrip step discontinuity and for a single-filter structure with interacting discontinuities, namely a coupled line filter. The filter characteristics are compared with measurements. Measurements verify the filter calculations