Post-processing removal of non-real characteristic modes via basis function perturbation

For more than 30 years since it was first proposed by Harrington et al., the Theory of Characteristic Mode (TCM) has only been applied to perfect electric conductors (PEC), and more recently lossless dielectric materials. One key challenge in computing the characteristic modes (CMs) of non-PEC materials using the PMCHWT surface integral equation is the presence of internal resonances in the solution space, due to the required forcing of symmetry on the impedance matrix. In lossless dielectrics, it was shown that these non-real CMs can be removed in post-processing through far-field power analysis. However, this method breaks down in lossy materials as it relies on the assumption of no radiation losses. This paper proposes the use of basis function perturbation to isolate the non-real CMs from the real CMs when CM analysis is applied to lossy materials.