A Two-Step Perturbation Technique for Nonuniform Single and Differential Lines

A novel two-step perturbation technique to analyze nonuniform single and differential transmission lines in the frequency domain is presented. Here, nonuniformities are considered as perturbations with respect to a nominal uniform line, allowing an interconnect designer to easily see what the effect of (unwanted) perturbations might be. Based on the Telegrapher's equations, the proposed approach yields second-order ordinary distributed differential equations with source terms. Solving these equations in conjunction with the pertinent boundary conditions leads to the sought-for currents and voltages along the lines. The accuracy and efficiency of the perturbation technique is demonstrated for a linearly tapered microstrip line and for a pair of coupled lines with random nonuniformities. Moreover, the necessity of adopting a two-step perturbation in order to get a good accuracy is also illustrated.