Scattering Operator eigendecomposition in the low frequency domain: Relationship between eigenvalues and surface impedance

The Characteristic Mode Theory is a valuable tool in RCS analysis. Although the mathematical framework is established in the context of PEC objects, we apply the eigenvalue decomposition on Scattering Operators of coated objects, which coating is modeled by an impedance condition on the surface. We show that the computed scattering operators exhibit the mathematical properties indicated by the theory, and exhibit an empirical möbius transform between the value of the impedance coating, and the first eigenvalue of the decomposition of the operator. This could be successfully used as a zero order model for the RCS of the object.