A novel finite element method-based technique for the calculation of all circuit parameters of an efficient broadband equivalent network representation of parallel-plane pairs with arbitrary geometry is presented. It is based on an eigenvalue analysis in combination with the solution of the quasi-static Poisson equation for the magnetic vector potential. Compared with a recently presented simple finite difference scheme, the suggested FEM approach considerably reduces the modeling and computational effort, enabling an adaptive meshing in the presence of small circular ports. The proposed approach is validated by a practical example, demonstrating the considerable computational savings and the versatility for practical applications.