  Conventional electric field integral equation based theory is susceptible to
the spurious internal resonance problem when the characteristic modes of closed
perfectly conducting objects are computed iteratively. In this paper, we
present a combined field integral equation based theory to remove the
difficulty of internal resonances in characteristic mode analysis. The electric
and magnetic field integral operators are shown to share a common set of
non-trivial characteristic pairs (values and modes), leading to a generalized
eigenvalue problem which is immune to the internal resonance corruption.
Numerical results are presented to validate the proposed formulation. This work
may offer efficient solutions to characteristic mode analysis which involves
electrically large closed surfaces.
