Research On Design And Characteristics Of Terahertz Reflective Scanning Array Based On Electronically Controlled Liquid Crystal

The wavelength of terahertz wave is between microwave and infrared,with high transmittance,broadband,coherence,transient,and low energy.It is widely used in various fields of scientific research and homeland security,in communications,radar And meteorology and other fields have great potential.The terahertz phased array is a key component of multi-beam modulation in the three major fields.By controlling the local phase of the wavefront,multiple independently controllable beams are formed to realize tracking,imaging and other functions.In the terahertz band,the properties of liquid crystals are relatively stable,and liq uid crystal-based terahertz phased arrays combine the advantages of high efficiency,broadband,and low loss.With the development of science and technology,researchers have put forward higher requirements for the resolution and integration of liquid crystal phased array devices in the terahertz band.Compared with the transmissive liquid crystal phased array,the reflective liquid crystal phased array has the advantages of small size,easy integration,low cost,and a lower working voltage.The application prospect of the terahertz waveband reflective liquid crystal phased array is broad.Considering the key performance of the phased array,the deflection angle and diffraction efficiency,this project aims to design a suitable size,large deflection angle,and high diffraction efficiency reflective liquid crystal phased array suitable for the terahertz band.First of all,the phase shifter is a subunit of the phased array,and the control performance of a single phased element directly determines the modul ation depth,scanning angle,scanning accuracy,and multi-beam scanning performance of the terahertz phased array.Taking the terahertz reflective phase shifter as the research object,prepare terahertz reflective phase shifters with different thicknesses,use terahertz time domain system to test the time domain spectrum and frequency domain spectrum,analyze the change of the time domain signal with the bias voltage,and explore Phase shift performance of phase shift devices with different thicknesses.Secondly,the multi-beam tracking capability relies on the complex electrode array structure,and the structure design of the electrode array also determines the beam deflection capability of the terahertz phased array.By designing a one-dimensional four-position phased array antenna structure,and simulating the electric field distribution of the terahertz reflective liquid crystal phased array with the reflective structure,the control performance of the reflective liquid crystal phased array on the terahertz beam is further studied.The relationship between the effective refractive index of the used LDn-type liquid crystal and the bias voltage is analyzed,and the factors affecting the deflection performance of the phased array of the terahertz liquid crystal are studied from the conditions of the voltage bias mode,the refractive index gradient and the beam incident angle.Finally,based on the designed one-dimensional four-phase phased array antenna structure,a terahertz reflective liquid crystal scanni ng array is prepared.Build a terahertz reflective liquid crystal phased array system,combine the simulation results,and adopt the optimal voltage bias method and beam incidence angle to test the beam deflection performance of the reflector array.In the terahertz band,a beam deflection angle of 3.86° was achieved,and diffraction efficiency reached 84%.The theoretical and experimental research on reflective phased arrays in this thesis promotes the application process of terahertz reflective phased arr ays and enriches the research content of terahertz wave quasi-optical modulation devices.