Fusing Leontovich Boundary Conditions and Scalar 2D FEM to Compute Lid and Lateral Wall Losses in H-plane Waveguide Devices

This paper introduces a 2D FEM for analyzing H-plane waveguide devices with conductor losses. The method is initially formulated for the ideal lossless case and then extended to account for conductor losses, utilizing a scalar formulation that seamlessly integrates the Leontovich boundary condition on both lid and lateral walls. For the lids, the boundary conditions introduce a first-order correction in the wavenumbers used in the field formulation, which are combined with the losses in the lateral walls through an additional matrix involved in the FEM system. Numerical validation is carried out on several examples, including an inductive filter with rounded corners and a K-band diplexer, where conductor losses play a critical role. The results demonstrate the accuracy and computational efficiency, showing excellent agreement with both analytic (when possible) and commercial software simulations based on 3D-FEM, offering a highly efficient alternative to traditional 3D techniques for waveguide analysis and design.