LAUSR

This paper describes a novel helical antenna made of pure water. The water helical antenna is realized by replacing the metallic arm of a conventional helical antenna with a plastic tube of circular cross section filled with pure water. The axially symmetric TM01 mode is excited along the water arm and accounts for the wave propagation and radiation. Circular polarization (CP) is achieved by choosing a proper dimension of the water helix. The measured results show that the proposed water helical antenna has an overlapping impedance bandwidth ( $\vert \text{S}_{11}\vert < -10$ dB) and an axial ratio (AR) bandwidth from 1.27 to 2.13 GHz, or 50.6% fractional bandwidth. A water helix antenna with polarization reconfigurability is also designed and demonstrated. The measured results show that the proposed helix antenna exhibits polarization-reconfigurable capability over a wide frequency band.