Research On Hybrid Wide-band Water Antenna

With the development of wireless communication systems,such as miniaturization,broadband and high efficiency,the antenna should also focus on the research of small size,wide-band and multi-function.Meeting the requirements of the system is becoming more and more difficult for traditional antennas because it is not easy to combine multiple performance.The proposed liquid antenna opens up a new way for the development of antenna.Among them,water antenna has been widely studied for its high transparency,low radar cross section,strong fluidity and other characteristics.Pure water has a very high relative dielectric constant,so it can effectively reduce the antenna size when making dielectric resonator antenna,but it also brings the problem of narrow bandwidth.Based on the existing water antenna theory,the wide-band of pure water dielectric resonator antenna,pure water dense dielectric patch antenna and hybrid water antenna are studied in detail in this paper.On this basis,the frequency and circular polarization of the antenna can be respectively configurated by using the fluidity of pure water to realize the functional diversity of the antenna.The specific work is as follows:1.A wideband reconfigurable hybrid water dielectric resonator antenna is proposed.The antenna consists of a cylindrical container made of Plexiglas and a cylindrical coaxially feed probe.The cylindrical container is supported on the ground by four small plexiglass columns,introducing a layer of air dielectric.Pure water is filled into the cylindrical container.Under the action of a feeding probe,the mode of the cylindrical pure water dielectric resonator is excited.At the same time,the interface between pure water with a high dielectric constant and air with a low dielectric constant is equivalent to an electrical wall,which works in a similar way to a metal patch antenna,exciting the air below to produce the cavity mode.The coaxial probe not only acts as the feeding structure,but also participates in the radiation of the antenna as a monopole.When the water dielectric resonator,air cavity mode and monopole work together,the impedance bandwidth of the hybrid antenna reaches 42.8%(3.3 GHz-5.1GHz)when S₁₁<-10 d B.The introduction of air layer not only expands the bandwidth,but also reduces the loss of the antenna by taking advantage of the fact that the electromagnetic field energy tends to concentrate in the dielectric with a relatively small dielectric constant.The proposed antenna has the radiation efficiency of 70%and the gain of 3.0 d Bi-6.0 d Bi.The cylindrical pure water dielectric resonator is the main radiation structure of the antenna.By tuning the height of the cylindrical pure water dielectric through the top water injection hole,it can be reconfigurable in the frequency band of 3.1 GHz-4.9 GHz and 3.4 GHz-5.2 GHz.The radiation pattern of the antenna is stable in the available frequency band,and the simulated results are in good agreement with the measured results.2.A water dense dielectric patch antenna with wide-band and circular polarization reconfigurability is proposed.The antenna is made of a square Plexiglas container and an L-shaped coaxial feeding probe.The circular polarization of the antenna can be configurated by pumping pure water into or out different cavities.Since the antenna structure is symmetrical,the available bandwidth of left-hand and right-hand circularly polarized radiation states is approximately equal.The axial ratio bandwidth of the antenna is as wide as the impedance bandwidth,which makes full use of the impedance bandwidth.This is because under the action of L-shaped coaxial feeding probe,the pure water dielectric resonator resonates at 3.6 GHz to form circularly polarized radiation.The large difference of the relative dielectric constant between pure water and air makes its interface similar to an electric wall,which causes the cavity mode of the air layer to be excited and produce resonance at 3.3 GHz.The two resonators work together to generate circularly polarized radiation over a wide frequency range.The measured results show that when S₁₁<-10 d B,the 3-d B axial ratio bandwidth is greater than24.4%(3.09 GHz-3.95 GHz),the radiation efficiency is concentrated between 58%-71%,and the maximum gain is up to 3.5 d Bi.Under the two circularly polarized states,the antenna maintains a stable circularly polarized radiation within the available bandwidth.Compared with other circularly polarized reconfigurable liquid antennas,the proposed antenna has a lower profile or higher radiation efficiency while maintaining a wider available bandwidth.3.A wide-band circularly polarized hybrid water dielectric patch antenna is proposed.The main structure of antenna is a container made of Plexiglas,which is used to hold pure water.Four plexiglass rectangular brackets connect the container to the floor,and a layer of air is introduced between them.The lower part of the container is connected to a metal patch printed on an FR4 substrate.The antenna can form a wide axial ratio bandwidth and impedance bandwidth.The pure water patch not only acts as the dielectric resonator to form circularly polarized radiation,it also forms a layer of electrical wall at the interface with the lower air,which causes cavity mode resonance of the lower air dielectric and forms circular polarized radiation.As the dielectric loading of the metal patch antenna,the resonant frequency of the metal patch moves to low frequency,expanding the bandwidth of the antenna.The three parts work together to form a wide axial ratio bandwidth.The combination of L-shaped feeding probe and FR4 substrate makes the coupling feeding better,thus forming a wider impedance bandwidth.Measured results show that when S₁₁<-10 d B,the available bandwidth(3-d B axial ratio)of the antenna reaches 50.8%(2.2 GHz-3.7 GHz),the radiation efficiency is 50%-65%,and the gain is 1.0 d Bi-4.8 d Bi.It can form stable circularly polarized radiation in the available frequency band.Compared with other wide-band circularly polarized liquid antennas,the proposed antenna has higher impedance bandwidth utilization and wider axial ratio bandwidth.