A Research Of Terahertz Phase Shifting Properties Based On New Materials

With the development of the terahertz application technology,terahertz phase shifters with continuously adjustable phase characteristics have become increasingly important.Now,research of domestic and foreign on phase shifters mainly starts from the following two aspects: adjustable materials and advanced technology.There are many new materials which is adjustable,including graphene and liquid crystal.Liquid crystal is an anisotropic and birefringent material controlled by voltage bias,which is very suitable for terahertz phase shifters.Based on the transmission line structure of liquid crystal material,the theoretical analysis and the simulation research of terahertz phase shifter are carried out in this thesis.This paper first studies the terahertz phase shifter based on the microstrip line structure of liquid crystal materials,and then designs a model and performs simulation.The signal line width,the length of the cut corner of the signal line,and the thickness of the liquid crystal layer are optimized in simulation.Because the microstrip line has high loss in the high frequency band and is easy to excite high-order mode electromagnetic waves,the simulation results have reached the phase shift of 102°/mm at 320 GHz,but the insertion loss has reached-2.5dB.In order to solve the problems existing in the terahertz phase shifter based on liquid crystal microstrip lines,a coplanar waveguide type terahertz phase shifter based on liquid crystal materials is explored further.The slot width,thickness of the liquid crystal layer,and the depth of the slot are compared.The effect of the phase shift performance of the device is optimized and the simulation is performed.The insertion loss ratio of terahertz liquid crystal phase shifter with the microstrip line structure,has been significantly reduced,but the phase shift amount is too small which is 33°/mm.In order to obtain a sufficient amount of phase shift while having a small insertion loss,a terahertz phase shifter based on an artificial spoof surface plasmon polariton(spoof surface plasmon polariton,SSPP)structure and liquid crystal materials is designed in this paper.The surface wave is excited by an ideal conductor with a special periodic surface structure.The phase shifter is propagated in the liquid crystal.From a plane view,the phase shifter is composed of a coplanar waveguide structure,a coplanar waveguide to an artificial surface plasmon waveguide.This paper focuses on the analysis of the influence of the structure size of theartificial surface plasmon unit on its dispersion curve,and the effect of the structure of the artificial surface plasmon unit,the thickness of the liquid crystal layer,and the bias circuit on the phase shift characteristics of the phase shifter.Optimize the simulation to get the optimal structure.The insertion loss of the terahertz phase shifter based on the artificial surface plasmon structure of the liquid crystal material reached-1.9dB,and the phase shift amount also increased to 55°/mm.