Tapered rectangular transmission lines are widely used in electromagnetic compatibility (EMC) and microwave integrated circuits (MIC). Electromagnetic wave propagation in this kind of transmission line is discussed. A coordinate transformation for analyzing the transmission line is presented. The derived wave equation is a second-order nonlinear partial differential equation which is solved by using Galerkin method. An application of this method is also given, good agreement is seen between the computed and measured results.
"Coordinate transformation for analyzing the tapered rectangular transmission line", Proc. SPIE 2211, Millimeter and Submillimeter Waves, (19 August 1994); doi: 10.1117/12.182979; https://doi.org/10.1117/12.182979