Evaluation of eigenmode quality factor of large complex cavities based on PEC linear finite element formulation

Finite conductivity losses of arbitrarily shaped and inhomogeneously loaded two- and three-dimensional structures are evaluated to a practical accuracy, solving a linear eigenproblem formulated on perfect electric conductors (PECs). This scheme mimics the analytical approach classically employed for canonically shaped waveguides and cavities. The normal electric and tangential magnetic modal fields, obtained assuming all metallic surfaces as PECs, are practically unchanged in the finite conductivity case. These are utilised to evaluate the previously vanished tangential electric and normal magnetic field components through the Leontovich impedance conditions and in turn the related attenuation factors for 2D and quality factors for 3D structures. Validation against commercial electromagnetic simulators and nonlinear FEM formulations incorporating Leontovich conditions yields an agreement better than 2%.