Characteristic mode assisted design of dielectric resonator antennas with feedings

The theory of inner resonant modes (IRMs) is very useful for the analysis and design of dielectric resonator antennas (DRAs), but it suffers from several limitations including canonical DRA shapes, high permittivity substrate, and large errors. Characteristic modes (CMs) contain similar physical insights but without the limitations owing to its full-wave nature. In this paper, a new approach is proposed for the codesign of DRAs and feeding structures using CMs. The volume-surface formulation combining substructure treatment is adopted to calculate CMs of DRAs. To detailedly demonstrate the proposed method, electric and magnetic feeding structures are utilized to excite a cubic DRA as examples. Compared with the results obtained by an isolated design of DRAs and feeding structures, characteristic mode analysis (CMA) of the whole structure reveals several new modes, in which the lower order modes correspond to much lower resonant frequencies. Proper modifications of the feeding structures can effectively excite these modes and result in dual- and triple-band operation. Several prototypes were fabricated and measured for verification. For a cubic DRA with a side length of 25.4 mm, it achieves a triple-band operation at 1.6, 3.1, and 4.6 GHz. Therefore, this method is ideal for the codesign of arbitrary DRAs with feeding structures.