Research On Holographic Beam Reconfigurable Antenna Based On Liquid Crystal

In recent years,with the development of modern wireless communication systems,how to achieve excellent performance and high reliability at a lower cost has become a research focus of most scholars,and reconfigurable technology is regarded as one of the ways to solve the above problems.At the same time,with the continuous progress of materials science,a lot of new materials with excellent performance have appeared in the field of microwave,among which liquid crystal is one of the representatives.It has anisotropic characteristics and excellent linear tuning ability in the microwave frequency band.Compared with the traditional reconfigurable technology,it can not only realize continuous adjustment,but also has the characteristics of low loss,easy integration and low cost.By using the tunable properties of liquid crystal materials and the large Angle beam forming ability of microwave holographic antennas,the problems of poor linearity,large loss and small reconfigurable range of traditional beam reconfigurable antennas can be solved.Based on the above subject background,this thesis carries out the research of holographic beam reconfigurable antenna technology based on liquid crystal.The main work of this thesis is summarized as follows:1.The principle of holographic amplitude regulation is analyzed and verified.Firstly,the amplitude modulation formula of microwave holography is derived and verified with the symmetric oscillator array.In this process,the existence of conjugate beam is found.In order to eliminate the influence of conjugate beam,the variable k_s is introduced,and the radiation of conjugate beam is suppressed by setting reasonable k_s value.2.Carried out the research and design of liquid crystal electronic control tuning theory and its dielectric characteristics test system.The classification of liquid crystal materials and the characteristics of all kinds of liquid crystals are described,and the process of nematic liquid crystal affected by bias voltage is further analyzed.Secondly,several typical dielectric constant testing methods are introduced and a liquid crystal dielectric constant testing circuit is designed by using inverted microstrip structure.3.The design of holographic leak-wave antenna based on liquid crystal materials is carried out.Based on the substrate integrated waveguide structure,a holographic leak-wave antenna with a center frequency of 35 GHz is designed.Combined with the tunable properties of liquid crystal materials,the beam reconfiguration function of the antenna at a fixed frequency is realized.The simulation results show that when the dielectric constant of the liquid crystal changes from 2.5 to 3.2,the antenna main beam direction will change from 45°to 55°.The main beam gain fluctuation is less than 1,ranging from14 d Bi to 14.8 d Bi;The sidelobe level is always below-10 d B.Since a holographic antenna radiates from a single frequency point,in order to define the bandwidth of the antenna,the frequency range of the antenna when the antenna gain drops by 3 d B in the direction of the main beam is defined as its bandwidth.The simulation results show that when the working frequency of the antenna drops to 34.4 GHz and rises to 35.9 GHz,the decrease range of the main beam gain does not exceed 3 d B,so the bandwidth of the antenna is considered to be 1.5 GHz.4.The design and research of coding holographic antenna are carried out.In order to give full play to the advantages of large Angle beam forming,a holographic antenna with large Angle beam reconfiguration function is designed.In order to optimize the design method of the array,the holographic amplitude control formula is optimized so that the array elements only have two states of“0”and“1”.Firstly,a codible holographic leak-wave antenna with an operating frequency of 16 GHz is designed,which can achieve beam reconfigurable range of-60°～60°,but its gain is low.In order to improve the gain of the antenna without increasing the length of the antenna,the transverse array is used to improve the gain,and an eight-part substrate integrated waveguide power splitter is designed to feed.In order to realize the individual control of each liquid crystal unit,the AD5370 is controlled by MCU as the main control chip to realize the voltage division in the way of digital-to-analog conversion and to realize the output of adjustable voltage for each way.The simulation and test results show that the beam reconfigurable range of the antenna is-60°～60°,the maximum gain is 17.5 d Bi,and the antenna bandwidth is 15.8GHz～16.3 GHz.