Research On Millimeter-wave Electronically Beam-scanning Array Based On Liquid Crystal

With the development of millimeter wave and terahertz technology,electrotuning devices made of liquid crystal are more and more widely used.Planar arrays combined with liquid crystal electro-tuning devices have the characteristics of miniaturization,low loss,low cost,high resolution and high precision beam orientation in millimeter wave band.In order to achieve continuous beam scanning,electronically controlled beam scanning arrays based on liquid crystal have become a research hotspot.Planar reflectarrays have been extensively studied because of their high gain and strong beam directivity,but some key problems still need to be solved urgently.Existing millimeter wave planar reflectarrays can only scan one-dimensional beams with limited scanning range.In order to expand the beam scanning range and realize electronically controlled two-dimensional beam scanning,this paper will study and design the reflection element and array structure.The phase shifting capability of the reflector element and the electronically control network of the array elements are the difficulties of the research.To solve the above problems,first of all,based on the electronically controlled phase-shifting characteristics of liquid crystal,a reflection element based on liquid crystal is designed.By designing multi-resonant structure,the phase-shifting ability of the reflection element is enhanced,which establishes the basis for the phase of the precise array control unit.Then,a novel driver-line network scheme is proposed.Combined with subarray division,the floor is divided,and the driving line of control element voltage is distributed in the patch layer and floor layer of the array,which effectively reduces the influence of the driving line on the performance of the array.Finally,the designed reflectarray can scan 50° beam in the area where the feed is located,and 40° beam in the area perpendicular to the feed surface,thus realizing the two-dimensional electronically controlled beam scanning in a large angle range.However,the defect of the reflectarray is that the horn feed shields the radiation waveform,which limits the beam scanning range.In order to solve this problem,the beam scanning transmitarray based on liquid crystal will be studied and designed in this paper.The transmitarray can avoid the feed occlusion effect.Because the phase shift of liquid crystal transmission element is very limited,a new method is needed to control beam direction without phase control,that is,beam control method based on holographic theory and only amplitude control.Firstly,a liquid crystal amplitudecontrolled transmission element is designed.While adjusting the liquid crystal to achieve amplitude control,the phase change is reduced.Then,the feasibility of beam scanning is verified by the principle of holographic amplitude control.Finally,the random incident phase introduced by space feeding is used to suppress sidelobes and achieve a beam scanning of ±30°.