Study on Characteristic Mode Analysis of Three-Dimensional Conducting Objects in Lossless Layered Medium

We comprehensively study the characteristic-mode analysis (CMA) of arbitrarily shaped 3-D conducting objects embedded in a lossless planarly layered medium. The electric field integral equation (EFIE) with the layered medium Green's function is applied as the core equation for numerical analysis. The modal behavior of an object in a layered medium is first comparatively studied with that in free space. The low-frequency breakdown problem of the EFIE-based CMA and its remedy is then elaborated. The asymptotic frequency dependence of the characteristic eigenvalues for the low-order modes is numerically investigated. A theoretical analysis is conducted by constructing a frequency-independent generalized eigenvalue problem and applying Taylor expansions. Finally, the modal expansion for scattering problems and parameter extraction for circuit problems are discussed, both in the context of a layered background. Since the electromagnetic property of an electrically small object is mainly governed by a few of low-order modes, this paper may provide an effective way of model order reduction for complicated structures residing in a layered medium.