An efficient finite element approach for the analysis of three-dimensional transmission line discontinuities using an asymptotic boundary condition

A novel technique is developed for efficient finite-element solution of open-region three-dimensional transmission line structures in the quasi-TEM (transverse electromagnetic) regime. Starting with the general form of the solution to the three-dimensional Laplace equation in spherical coordinates, a set of asymptotic boundary condition (ABC) operators is derived. The second-order ABC is then applied on a conformable outer boundary for the purpose of truncating the finite-element method (FEM) mesh in an efficient manner. To illustrate its application, the method is used to compute the capacitance of a rectangular microstrip patch and the results are found to be in good agreement with published data.<>