Research On The Liquid Antenna In Ultra-short-wave Band

With the fast development of wireless communication technology,the performance requirements of antennas for communication systems are getting higher and higher.The antennas made of traditional metal material shows many shortcomings,as a consequence,using liquid material to design antennas has become a hot research direction.The most common liquid materials include: electrolyte,liquid metal,etc.In recent years,many antennas with liquid metal as the radiator have been designed,and such antennas have reconfigurable characteristics.In contrast with the high cost of liquid metal and the inevitable pollution after waste,in this thesis,we use seawater or common strong electrolyte aqueous solutions as the radiator to design a series of liquid antennas for ultra-short-wave communications,and we focus on the design theory and method of the wideband liquid antennas.Compared with the traditional metal antennas,those designed with seawater have some promising advantages,such as green,corrosion resistance,easy to obtain,low cost,stealth,and invulnerability.Moreover,he designs of reconfigurable antenna based on the fluidity of liquid has a high application value in practical engineering.In addition,due to a high dielectric constant of seawater,it is very helpful for the miniaturization of the antennas.First,this paper introduces some useful antenna parameters and the basic design theory of monopole antennas,and then analyzes the electromagnetic characteristics of seawater,which provides basic theory support to the design of liquid antennas.Second,according to the design theory of the monopole antennas,we designed a liquid monopole antenna,including the dielectric shell,the antenna feeding structure,and the frequency reconfiguration method.The liquid monopole antenna meets the communication requirements of ultra-short-wave band,with narrow band and good omni-directional characteristic.The resonant frequency of the antenna can be changed by changing the height of the sea water column.Third,based on the liquid monopole antenna,a cylindrical coupling structure broadband liquid antenna in ultra-short-wave band is proposed.By introducing the parasitic liquid structure,the parasitic resonant frequency is also increased,so the bandwidth of the antenna can be expanded.Changing the size of the radiating unit and the parasitic unit respectively,we can adjust the parasitic resonance frequency to fall near the antenna's working frequency,as a result,the relative bandwidth reaches 110.4%.Because the parasitic element is asymmetrical,the omni-directional characteristic of the broadband liquid antenna is unsatisfactory.And then,a symmetrical cylindrical coupling structure broadband liquid antenna is proposed,the omni-directional characteristic is greatly improved.The bandwidth of the antenna is further expanded,and the relative bandwidth reaches 111.4%.This kind of broadband liquid antenna meets the communication requirements of ultra-short-wave band.The bandwidth is wide and reconfigurable,the structure is simple and easy to maintain.Finally,the previously proposed liquid antennas are based on the monopole antenna.Theoretically,an infinitely large conductive ground is needed as the ground,which cannot be realized in practice.In order to thoroughly implement the concept of liquid antenna,we designed a liquid antenna feed structure using seawater as a conductive ground.Compared with metal floor,the performance of the antenna using this seawater ground is equivalent to that of using metal ground.Because of the high dielectric constant of seawater,the size of the antenna can be further reduced by using seawater ground.The ability of sea water to reflect electromagnetic wave is weaker than that of metal,so it can also reduce the radar cross section of the antenna.In addition,using sea water as the conductor ground can further reduce the metal usage of the antenna,and also provides a valuable reference for the design of liquid antenna.