Fusing leontovich boundary conditions and scalar 2-D FEM to compute lid and lateral wall losses in H-Plane waveguide devices

This letter introduces a 2-D finite-element method (FEM) for H-plane waveguide devices, initially formulated for the ideal lossless case and then extended to include conductor losses. A scalar formulation naturally incorporates the Leontovich boundary condition on both the lid and lateral walls, with a first-order wavenumber correction at the lid walls and an additional matrix for lateral wall losses. Numerical results including an inductive filter and a K-band diplexer show excellent agreement with both analytic (when possible) and commercial software simulations based on 3D-FEM, confirming the method's accuracy and efficiency for practical waveguide device analysis and design.