A Hemispherical Helical Water Antenna Array for Directional High-Gain Radiation

This letter proposed a water antenna with a novel shape of a hemispherical helix made of pure water. A plastic water pipe is bent into a hemispherical helix and filled with water to form the helical arm of the antenna. The water arm acts as a director, which enables the antenna to obtain wide-angle radiation characteristic in the axial direction with a beam width of 95.5°. The impedance bandwidth of the antenna (S11 < −10 dB) is 1.30–1.89 GHz. Based on this antenna, a four-element antenna array is also designed. A quasi-Butler matrix is used to feed this antenna array to achieve a reconfigurable pattern. The antenna array can achieve directional high-gain radiation in five directions, covering a total range of 66°. The maximum gain of the array in the effective frequency band can reach 13.8 dBi.