The equivalent circuit of a via that connects two semi-infinite microstrip transmission lines imbedded in a dielectric medium above a ground plane is considered. The T-type equivalent circuit consists of an excess capacitance and an excess inductance. The excess inductance of the via is the same as the one computed in the case of free space (without a substrate). The excess capacitance of the via is computed quasi-statically by the method of moments and the image method from the integral equations. Parametric plots of the excess capacitance of the via are given for reference.>

Evaluation of the time-domain response of multiconductor transmission lines is of great importance in the analysis of the crosstalk in fast digital circuit interconnections, as well as in the analysis of power lines. Several techniques for the computation of the line response, starting from the known circuit-theory parameters, are presented and evaluated. These methods are: time-stepping solution of the telegrapher equations, modal analysis in the time domain, model analysis in the frequency domain, and a convolution technique which uses line Green's functions. The last method can treat the most general case of lossy transmission lines with nonlinear terminal networks. Numerical and experimental results are presented to illustrate these techniques and to give insight into the crosstalk problems in fast digital circuits.