Effects of dielectrics and internal resonances on modal analysis of terminal chassis

The symmetric PMCHWT method of moments (MoM) impedance matrix allows for the characteristic modes (CMs) of a structure containing dielectric to be found. Recently, this impedance matrix was proven to provide non-real solutions which can be attributed to the MoM internal resonance problem. These internal resonances can be removed through different CM post-processing techniques. However, these studies focus on dielectric structures, whereas the majority of antennas utilize electric conductors as the radiators. As such, dielectrics are often neglected to simplify the CM analysis and hence the problem of internal resonance is overlooked. This work explores the extent of the internal resonance problem in mixed conductor-dielectric structures. The results reveal that the problem is severe even when the structures only contain small amounts of dielectric materials. Moreover, the significant impact of dielectrics on CMs reveals that dielectrics should be included in CM analysis to ensure high accuracy.