Terahertz Reflective Electronically Controlled Scanning Antenna Based On Liquid Crystal

In recent decades,with the rapid development of terahertz technology,terahertz radiation devices with beamforming functions have become more and more widely used in wireless communication,radar systems,medical imaging and diagnostics,and security detection.Reconfigurable reflectarray antennas have attracted more attention due to its high gain,low loss,low sidelobe level and beamforming.The liquid crystal-based electronically controlled scanning antenna can use the liquid crystal to change the reflection phase of each array element to realize the beamforming capability.In this thesis,a double dipole phase shifting unit in the terahertz band is designed by liquid crystal.Based on the unit,the structure of the electronically controlled scanning antenna is designed.Firstly,the electronically controllable dielectric constant of the nematic liquid crystals is introduced.The dielectric constant and loss tangent of E7,S200 and HFUT-HB01 at 100 GHz and 300 GHz are measured by terahertz time-domain spectroscopy(THz-TDS)system and frequency selective surface(FSS).The ?ε of HFUT-HB01 was the largest,reaching 1.1 by comparative analysis of the test results.Then,a double dipole phase shifting unit based on liquid crystal material is designed.The reflective characteristics of the terahertz electromagnetic waves are calculated and analyzed.The influence of structural parameters on phase shifting performance is studied.The ability of the liquid crystal to adjust the phase of the unit is proved by simulation results.The sample was fabricated,which is an array consisting of 40×40 patch elements,printed on a 4×4 cm quartz substrate with 1 mm thickness.The maximum phase shift of the unit is 428.5° at 334.025 GHz.The bandwidth of the phase shift range exceeding 360° is 7.575 GHz.Finally,an electronically controlled scanning antenna composed of 30×30 array elements is designed based on the double dipole structure.The simulation results show that the antenna can realize the beam scanning function of ±25°,the maximum gains at beam angles of 0°,12.5°,and 25° are 24.5 dBi,23.6 dBi,and 20.2 dBi,respectively.The research content of this thesis provides a design idea for the reconfigurable reflectarray antenna in the terahertz band.