Research On The Broadband Beam Scanning Technology Of Reflectarray Based On Liquid Crystals

In modern wireless communication systems,there is a remarkable demand for high performance,multi-functional,cost-effective and compact devices.In this context,antennas are critical or even limiting components having impact on system performance,cost and compactness.With the development of technology,reflectarray has received more and more attention in the field of antenna engineering because of its multiple advantages such as low profile,low cost,high efficiency,easy conformity,and easy reconstruction.It is of great theoretical significance and engineering value to explore and innovate new methods and technologies for the design of reflectarray and continuously improve their performance parameters to suit more applications.This paper adopts a research method combining theoretical research,simulation analysis and physical measurement verification.A series of design,simulation and experimental studies are carried out around broadband,beam scanning and liquid crystal tuning technology in this paper.Firstly,the working principle of reflectarray is introduced.Secondly,the microwave characteristics,the measurement methods of dielectric constant,simulation modeling and packaging technology of liquid crystal materials are introduced and a example design of liquid crystal microwave tunable devices is given.Finally,the frequency band and phase shift characteristics of the liquid crystal reflectarray cell and the true-delay line loaded liquid crystal reflectarray cell are analyzed,and the design examples and experimental results of them are given.The research results and innovations of this paper are as follows:（1）The tuning properties of the liquid crystal material in the microwave frequency range were studied.Aiming at the deficiencies of traditional tuning techniques,this paper studies a new type of liquid crystal tuning technology,analyzes the tuning principle of liquid crystal materials in the microwave frequency range,measures the dielectric constant and loss,and proposes a new type of the design method of microwave continuous adjustable coupler for liquid crystal material was processed and measured.The experimental results show that the microwave-based reconfigurable device based on liquid crystal material has good performance.（2）The sub-wavelength multi-resonant reflectarray cell based on liquid crystal material was studied.Aiming at the problems such as the poor linearity of the phase curve,the lack of phase shift range and the narrow bandwidth of the liquid crystal resonant reflector,this paper presents a sub-wavelength multi-resonant sinusoidal dipole element based on liquid crystal material,using four sine dipoles.The sub-cell structure achieves a linear phase shift exceeding 400⁰ in the0.3?₀ sub-wavelength grid by changing the liquid crystal bias voltage.The cell bandwidth is increased from 7%to 11.4%,compared with the liquid crystal triple-resonator dipole cell,and the performance are significantly improved.（3）A true-delay line loaded reflectarray based on liquid crystal material was studied.Aiming at the problem of insufficient phase shift of the conventional resonant liquid crystal reflective unit,this paper presents a spiral delay line loading type liquid crystal reflective unit technical scheme and analyzes the relationship between the unit phase shift amount and the delay line length.By changing the external bias of the liquid crystal material,a phase shift exceeding 360⁰ with a good linearity and 10.4%bandwidth can be obtained.