Computational Analysis and Verifications of Characteristic Modes in Real Materials

Despite its long history, the theory of characteristic modes (TCMs) has only been utilized in antenna design for perfect electric conductors (PECs). This is due to computational problems associated with dielectric and magnetic materials. In particular, the symmetric form of the Poggio-Miller-Chan-Harrington-Wu-Tsai (PMCHWT) surface formulation for the method of moments (MoM) solves for both external (real) and internal (nonreal) resonances of a structure. The external resonances are the characteristic modes (CMs), whereas the internal resonances are not. This paper proposes a new postprocessing method capable of providing unique and real CMs in all physical mediums, including lossy magnetic and dielectric materials. The method removes the internal resonances of a structure by defining a minimum radiated power, which is found through utilizing the physical bounds of the structure. The CMs found using the proposed method are verified through the use of an MoM volume formulation, time domain antenna simulations, and experiments involving multiple antenna prototypes.