Advancements, Challenges, and Prospects of Water-Filled Antennas

In the group of liquid antennas, water antennas have attracted tremendous popularity due to the excellent electrical and mechanical properties of water. Pure water is a high permittivity dielectric liquid which comprises high dielectric constant and very low electrical conductivity. While the electrical conductivity of pure water is very low, salt-water has good electrical conductivity. The electrical conductivity of salt-water can be controlled by adjusting the ratio of salt content (salinity) in the water solution. Both pure water and salt water has excellent optical transparency, liquidity, flexibility and easy availability, thus, become excellent candidates in antenna manufacturing. Pure water is utilized as the dielectric component of the antenna and generally used in the development of dielectric resonator antennas, whereas salt-water is used as the conductive part of the antenna replacing metallic conductors. Some antennas have also utilized both the pure water and salt water for improved performance. In the literature, different classes of antennas can be found that have been developed by utilizing water. In this review paper, we have highlighted the state-of-the-art designs of water-filled antennas, highlighted the major challenges towards the development of water-filled antennas and presented the novel applications and prospects of water-filled antennas.