Dual-band directional/omni-directional liquid dielectric resonator antenna designs using characteristic modes

Compact and low-cost dielectric resonator antennas (DRAs) at low frequency are preferred in many applications. In this work, we propose to design compact dual-band directional/omni-directional DRAs by properly exciting the characteristic modes (CMs) of a water filled glass bottle. Because the water has a very high permittivity of ε_r = 81, the resulted DRA is much smaller than other DRAs reported for 2 GHz band. By exciting the CM at the natural resonant frequency, the radiation efficiency is maximized. By introducing a resonant slot under the DRA, a dual-band operation is realized. Both the directional/omni-directional radiation patterns are obtained in this design. The antenna gain in the broadside radiation is higher than 5 dBi, which is the largest value reported for a water antenna.