Abstract
A fully planar amphibious antenna, capable of providing efficient radiation when surrounded by air as well as by water, is demonstrated. Benefiting from a dual-operational mode passive matching network that simply consists of a synthesized transmission line and a common delay line, the antenna is well matched in both the media with acceptable total efficiency. The synthesized line, comprising merely six quasi-lumped elements, functions identically to a conventional line in air, but automatically reconfigures as an open circuit in water. The design principle and synthesis procedure are introduced in detail. The planar antenna, with a size of $0.115 \,\, \times \,\, 0.094~\lambda _{0}^{2}$ and weighing 8 g, is operated in the 433-MHz industrial, scientific and medical (ISM) band. When surrounded by air and water, the measured −10-dB fractional bandwidths are 3.2% and 14.5%, respectively. The average gain and total efficiency are −3.6 dBi and 34.5% in air, and become −8.8 dBi and 15.4% when immersed in water.
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