An antenna is provided having a good matching characteristics when immersed in a fluid such as saline water, oil, or other liquids (“the phantom liquid”). In some embodiments, the antenna provides a tight capacitive coupling with the phantom liquid through the use of a higher permeability cover and absence of a gap between the cover and the antenna body. One embodiment employs a tunably capacitively loaded inverted “F” antenna structure. Additional embodiments of the invention provide an antenna tuning system that saves power by utilizing very low duty cycle periodical refreshing charge at a tuning varactor diode coupled to the antenna.