Research On Liquid Crystal Electronically Controlled Beam Steering Leaky Wave Antenna And Application

As a novel type of tunable material,liquid crystal(LC)material has been introduced into the microwave and millimeter wave fields from the optical field in recent years.Due to the excellent dielectric properties,continuous tuning and high linearity of LC,tunable microwave devices have been further developed.Leaky wave antenna(LWA)is a typical kind of traveling wave antenna with strong directionality and beam scanning characteristics.At the same time,it has the advantages of compact structure,simple design,easy feeding and low cost.The electronically controlled LWA composed of LC and LWA,has both advantages and challenges.In this paper,the technical difficulties in modeling,mechanism analysis,design optimization and packaging of electronic scanning LWA are studied,due to the flow pattern of liquid material in the LC control mechanism.The existing electronic scanning LWA based on LC is limited by the dielectric strength of LC,antenna unit structure and other factors.Thus the fixed frequency scanning range of LC based LWA in Ku band is limited.This paper extend the research of beam scanning range expansion method,and apply it to the spatial spectrum estimation.Instead of the traditional array antenna,this method realize the miniaturization antenna to solve the direction of arrival(DOA)estimation problem.Firstly,the characteristics of LC material in microwave band and the radiation mechanism of LWA are analyzed.Aiming at the liquid form of LC material,the strict requirements of processing technology and high cost of existing LC microwave devices,a microstrip-waveguide conversion mode LC electronically controlled scanning LWA is proposed.Through the design of coupling slot and feeding cavity,the conversion of electromagnetic wave from microstrip transmission mode to waveguide transmission mode at the feeding end of LWA is realized,and the purpose of electrical isolation between RF signal and DC bias voltage is achieved.Then the LWA filled with LC is realized.In this method,PCB processing technology and metal waveguide processing technology are combined organically to obtain good impedance matching,which provides a new solution for the realization of LC LWA based on waveguide structure.Secondly,in order to solve the problem that the LWA with uniform structure and periodic structure can not realize the lateral radiation,the theory of composite rightand left hand(CRLH)transmission lines is introduced.By combining the LC with the CRLH transmission line type LWA,the electronically controlled scanning LWA with forward and backward continuous beam scanning characteristics is obtained.Furthermore,the additional feeding network is avoided by the design ofthe connected short cut line.In addition,in order to obtain more flexible and accurate LC control mode and expand the scanning range of LC LWA,design method of CRLH transmission line LC dual tuning LWA is proposed.Through independent control and effective combination of two layers of LC,the realization method of LC dual tuning mode is obtained.Then,in order to further expand the beam scanning range of the CRLH transmission line LC electronically controlled LWA,a general dispersion sensitivity enhancement theory is proposed.By adding a unit structure with high dispersion sensitivity,the beam scanning range can be further expanded without changing the original antenna unit structure.And a high dispersion sensitivity cell structure based on LC material is designed.Combined with the CRLHLC LWA designed in this paper,this method can effectively expand the beam scanning range of the original antenna,and has universality,which is of great significance for improving the scanning range of the LC LWA.Finally,the LC electronically controlled beam scanning LWA with large scanning range is applied to the DOA system to replace the traditional large array antenna.The electronically controlled LWA and Estimation of Signal Parameters via Rotational Invariance Techniques(ESPRIT)algorithm is combined to propose the construction method of the array manifold matrix of the LWA subarray,and the algorithm is improved to be suitable for the electronically controlled LWA,and then the DOA estimation method of the electronically controlled LWA based on ESPRIT algorithm is obtained,which provides a prospective research value for realizing the miniaturization,low cost and low power consumption of the DOA estimation system.To sum up,the research content of this paper aims at the problems encountered in the practical application of LC based LWA.Based on the theoretical research,combined with full wave simulation and experimental verification,comprehensive scientific research is carried out,which provides solid theoretical basis and research value for the research and potential application of LC based LWA.