title: Investigations of water-based liquid antennas for wireless communications
Creators: name: Xing, Lei
Publisher: name: University of Liverpool Repository
Year: 2015

description: Water-based liquid antennas are a new type of antennas, which have attracted increasing attention in recent years. They have emerged as promising alternatives to traditional antennas for many applications. The purpose of this thesis is to present a comprehensive study into water-based liquid antennas, aiming at gaining a better understanding of water-based liquid antennas from the liquids used to the antenna designs. This thesis is comprised of two main research areas. The first area under investigation focuses on water-based liquid property characterisation. In water-based liquid antenna designs, a precise knowledge of the complex permittivity of the liquid is essential. Three water-based liquids, namely pure water, water with propylene glycol (PG) and salty water, are carefully studied from an antenna design point of view. A liquid measurement software package is developed to automatically record the liquid complex permittivity data under different temperatures, and measurements are conducted. The experimental data are processed to obtain accurate mathematical expressions for the complex permittivity of these liquids over a temperature range 0 ~ 70oC (for pure water and salty water) and -10oC ~ 70oC (for water with PG), frequency range 0 ~ 18 GHz, PG concentration 0 ~ 70% and salinity 0.1 ~ 50 ppt. Water with PG is proposed as an alternative candidate for pure water in cold climates. It is demonstrated that the performance of the antenna will not be changed significantly by using water with PG. The second area concerns water-based liquid antenna designs and is divided into three sections: The first section deals with the water antenna working as a conducting antenna. A water monopole antenna with a dielectric layer is designed. Salty water is used to replace the conducting material (usually copper) in traditional designs. A comprehensive parametric study is performed and the physical insights behind the design are studied. A close relationship between the salty water conductivity and antenna radiation efficiency is explored. The second section investigates the hybrid water antenna for hand-portable applications. By combining the resonance from the water dielectric resonator antenna (DRA) and that from the feeding structure, a wideband response can be achieved. Three hybrid water antennas are developed with low profiles and high efficiency. The unique features of water, namely liquidity and transparency are effectively utilised. A complex feeding structure is placed inside the water dielectric resonator (DR) to feed the water DR and also work as a radiating element. The third section relates to the water loaded reconfigurable antennas. Two water loaded reconfigurable antennas with special 3D folded structures are designed. Different technologies are applied in the reconfigurable designs such as the special folded 3D monopole structure, the use of water and its holder as a transparent dielectric loading, and the integration of an active component. The results show that the designs have compact sizes, reasonable efficiency and bandwidths. This thesis has successfully demonstrated the attractive features and great potential of water-based liquid antennas. The knowledge gained in this work is very valuable for future water-based liquid antenna development.