Research On Terahertz Reflectarray Antenna Based On Liquid Crystal

In recent years terahertz technology has a substantial development in the communications,nondestructive examination and biomedicine.As an important part of the THz application systems,the THz phased array antenna is still lacking,which limits the development of THz application technology.The liquid crystal phase shift provide an electronically phase shifting in millimeter and terahertz band,thanks to their excellent tunable permittivity.And the liquid crystal based reflectarray antennas has spurred huge research interests,due to their advantages of lower cost,miniaturized and flexible beam-scanning capability.The thesis mainly focuses on the design of the reflective liquid crystal phase shifter element and the reflectarray antenna in terahertz band.This thesis firstly analyses the dielectric property of the liquid crystal in the applied electric field,and the arrangement of liquid crystal molecules under different voltages have been deduced.The measurement methods of dielectric properties of liquid crystal have also been introduced in different frequency bands.A double dipole structures reflective phase shifter based on liquid crystal was proposed,and the characteristics of the unit was analyzed in simulation.The simulation results have proved the capability of liquid crystal to modulate the characteristic of the reflective wave,and show a phase shifting capability of liquid crystal phase shifter in sub-terahertz band around 350 GHz.An array constituted of patch elements was fabricated using the photolithographic process,and two liquid crystals of S200 and HFUT-HB01 have been used.The amplitude and phase of the reflection coefficient have been measured using vector network analyzer.The measurement results show that a phase shift of 240° was achieved at the frequency of 356 GHz of S200 liquid crystal.As for another HFUT-HB01 liquid crystal,it provided tunable phase range of 350 degree over the frequency range of 353.5 GHz to 359.3 GHz at 40 V,where a maximum phase shift 362.6° is achieved at 357 GHz?In order to improve the design accuracy,an accurate model considering both inhomogeneity and anisotropy of the liquid crystal was used to compare with the simplified model.A terahertz reflectarray antenna consists of 40×40 elements have been designed using the double dipoles elements based on liquid crystal.And the radiation characteristic of the antenna was simulated,and the simulated pattern show a beam scanning range of-20°~20° at the frequency of 340 GHz.The tunable terahertz phase shifters based on liquid crystal provide an effective solution for the design of electronically beam scanning antenna in the terahertz band.