Tunability of Liquid Dielectric Resonator Antennas

Dielectric resonator antennas (DRAs) have in the past been used most often at frequencies in the GHz portion of the spectra. This letter presents a novel 50-MHz DRA that uses water as the dielectric. For purposes of keeping the antenna tuned to a specific frequency, ande for using the antenna at different frequencies, this antenna can utilize a pump to alter the level of water in the DRA, thus, altering its resonant frequency. An electronic technique for retuning the feed probe is also presented where varactor diodes are biased to provide a good impedance match across a range of approximately 50 to 100 MHz. These antennas may provide a compact solution at lower frequencies especially where a directional pattern may be required. The liquid dielectric not only provides frequency tuning but simple deployment and a reducible radar cross section.