A Study On Water Reconfigurable Antennas

Along with the development of modern communication techniques,various wireless communication systems have raised increasingly higher requirements on the hiding and back-ground-fitness of antennas.Water antennas has been a hot topic in the past few years due to its high transparency,reconfigurable shape,and low cost.Reconfigurable water antennas are very promising in communication and radar system which have requirements on invisibility and conformalization with optical devices.This dissertation focuses on the theory and tech-niques to achieve reconfigurable water antennas.The main work is summarized as follows:1.A dual beam and omnidirectional beam reconfigurable water loop antenna is proposed:A novel water loop antenna is proposed in this section.This antenna uses annular arm made of pure water to take the place of the metallic loop of a typical loop antenna.The water arm is enclosed by a resin loop tube.Wideband and high gain can be achieved by well choosing the dimensions of water arm.When the tube is fully filled with water,the proposed water antenna works as a loop antenna.When the tube is partly filled,it looks like and also works as a water dipole antenna,which indicates pattern reconfigurability.Measured results show that when working in loop state,the impedance bandwidth of the antenna is from 0.9GHz to 2.3 GHz（87.5%）and a dual beam is obtained with a maximum gain of 4.7 dBi.When working in dipole state,the impedance bandwidth is from 0.8 GHz to 2.1 GHz（89.7%）,radi-ation pattern changed to omnidirectional and a maximum gain of 1.7 dBi is achieved.2.A pencil beam and conical-like beam reconfigurable water horn antenna is pro-posed:Based on the reflection of dielectric layer with high dielectric constant,a novel water wall rectangular waveguide is reported,which is realized by using water walls instead of tra-ditional metallic walls.Transport mode and leaky mode of the water wall rectangular wave-guide are studied.A water horn antenna is designed based on the water waveguide.Due to its fluidity,water can be readily controlled to fill different channels.Therefore,the proposed wa-ter horn antenna can operate in two states:H-plane horn state and open-end waveguide state,resulting in different radiation patterns.Measured results show that the antenna is able to ob-tain an impedance bandwidth of 70.1%from 2.5 GHz to 5.2 GHz for H-plane horn state and 74.7%from 2.6 GHz to 5.7 GHz for open-end waveguide state.A realized gain up to 10.5 dBi is achieved for the H-plane horn with a pencil beam under one state,and 7.8 dBi is obtained for an open-end waveguide leaky-wave antenna with a conical-like beam pointing-angle of 35°under the other state.3.A function-reconfigurable short backfire antenna made of water is proposed:A novel short backfire antenna realized by replacing the metallic wall with water wall is de-scribed.Through controlling the water flow in different layers,the proposed short backfire antenna based on a cylindrical waveguide made of water can switch between different func-tions:pencil beam short backfire antenna,pattern-reconfigurable conical beam antenna,and frequency reconfigurable monopole antenna made of pure water.When working in pen-cil-beam state,the proposed water short backfire antenna has an impedance bandwidth(|S₁₁|<-10 dB)of 11.3%（3.6 GHz to 4.05 GHz）.A maximum gain of 10.8 dBi is observed.While working in pattern-reconfigurable conical-beam state,the beam angle of a conical radiation beam can be switched between 25°and 60°.The operating frequency of the antenna working in pattern-reconfigurable conical-beam state covers a range of 5%（3.9 GHz to 4.1 GHz）.Maximum gain of 6.8 dBi for 25°and 2.7 dBi for 60°is obtained.When working in frequen-cy-reconfigurable monopole,the proposed water antenna has a tuning frequency range of 50%and a maximum gain of 2.7 dBi.A pattern reconfigurable water grating antenna with conical beam is proposed as the supplementary note of pattern-reconfigurable conical-beam state.The proposed antenna consists of several concentric water loops mounted on a glass cylindrical base fed by a probe from the back.A conical beam can be achieved when the dimensions of the structure are properly designed.By controlling the water flow of the loops,angle of the conical beam can be changed.This paper presents two situations of the water flow.Simulated results show that the proposed pure-water antenna can change the angle of conical beam be-tween 20°and 35°.Maximum gain of 10.8 dBi is achieved in 20°state and 9.5 dBi is achieved in 35°state.It should be mentioned that more angles can be achieved by employing denser water loops.4.Two polarized reconfigurable antennas made of pure water are proposed:The ra-diation principle of radiation mode in cylindrical dielectric waveguide is studied and used in water antenna design.The water helical antenna is obtained by replacing the metallic arm of a conventional helical antenna with a water arm which has a circular cross section.The effect of dimensions of the antenna is analyzed.Based on the structure,two prototypes with polariza-tion reconfigurability are designed.The characteristics of these two kinds of polar-ized-reconfigurable water antennas are concluded through comparison.One of them can switch between right-handed circular polarization（RHCP）and linear polarization（LP）.Measured results show that the proposed RHCP-to-LP antenna has an overall impedance bandwidth(|S₁₁|<-10 dB)of 87.9%for the two polarizations,and an axial ratio（AR）band-width（AR<3 dB）of 51.4%for RHCP.Maximum gain of 9.2 dBi for LP and 10.5 dBic for RHCP are obtained.The other one can be tuned between RHCP and LHCP.Measured results show that the antenna is able to obtain an axial ratio bandwidth of 50.3%from 1.27 GHz to 2.12 GHz with AR<3 dB for both LHCP and RHCP,a realized gain up to 10.5 dBi for RHCP and 10.1 dBi for LHCP are achieved.