Combined Source Integral Equation-Based Theory of Characteristic Modes for Impenetrable Bodies

The theory of characteristic modes (TCM) based on the combined source integral operator (CSIO) is developed for perfect electric conductors and for impedance boundary condition. This formulation is similar to the one based on the combined field integral operator (CFIO), circumvents the interior resonance problem appearing in the electric field integral operator-based TCM. The eigenvalues obtained by the CSIO-based formulation agree well with the analytical and numerical CFIO-based solutions. However, the eigenvectors of the resonating modes computed with the CSIO-based approach are found to be corrupted at the internal resonance frequencies.