Finite Element Based Eigenanalysis for the Study of Electrically Large Lossy Cavities and Reverberation Chambers

An eigenanalysis-based technique is presented for the study and design of large complicated closed cavities and particularly Reverberation Chambers, including conductor and dielectric material losses. Two different numerical approaches are exploited. First, a straightforward approach is adopted where the finite walls conductivity is incorporated into the Finite Element Method (FEM) formulation through the Leontovich Impedance boundary conditions. The resulting eigenproblem is linearized through an eigenvalue transformation and solved using the Arnoldi algorithm. To address the excessive computational requirements of this approach and to achieve a fine mesh ensuring convergence, a novel approach is adopted. Within this, a linear eigenvalue problem is formulated and solved assuming all metallic structures as perfect electric conductors (PEC). In turn, the resulting eigenfunctions are postprocessed within the Leontovich boundary condition for the calculation of the metals finite conductivity losses. Mode stirrer design guidelines are setup based on the eigenfunction characteristics. Both numerical eigenanalysis techniques are validated against an analytical solution for the empty cavity and a reverberation chamber simulated by a commercial FEM simulator. A series of classical mode stirrers are studied to verify the design guidelines, and an improved mode stirrer is developed.