Research On Electronically Scanned Array Technology Based On Liquid Crystals

Electronically controlled scanning array has been widely used in wireless electronic systems for different requirements due to its flexible and fast beam control system.Meanwhile,in order to reduce the size and cost of the antenna system and achieve the goal of high performance and multi-function array,electronically controlled scanning array with new working principles and materials are also gradually developing.Among them,liquid crystal,as a polymer material with electromagnetic controllable dielectric properties,is used as a tuning material of electronically controlled scanning pattern reconfigurable antenna.Compared with other reconfigurable antenna technologies,it can realize the advantages of continuous tuning,low high-frequency loss,low cost and easy integration.Therefore,based on the above research background,two kinds of electronically controlled array antenna based on liquid crystals are proposed in this paper.The main work is summarized as follows:1.The research on the principle of electronically controlled tuning technology of liquid crystal materials and the response time characteristics of liquid crystal materials are conducted.Firstly,the characteristics of nematic liquid crystals in microwave frequency band and the influences of orientational order parameter at different temperatures are discussed,and the electronic tuning process is also analyzed.Secondly,the influence factors of response time of microwave devices based on liquid crystals are studied.Finally,the test circuit and test platform for the response time of liquid crystals are discussed by microwave resonance method.2.The research of Ka band phased array antenna based on electronically controlled liquid crystal phase shifter is conducted.Aiming at the design concept of the phase shifter based phased array antenna,a LC-based reflective phase shifter of 1×4 planar phased array antenna is designed in Ka band.The phased array antenna uses the multi-layer PCB processing technology to realize the integration and miniaturization design.The phased array antenna structure consists of the planar magneto-electric dipole antenna unit,the LC-based reflective phase shifter and power division network including the bias circuit and the DC blocking circuit.At the same time,a four-way FPGA-based adjustable power supply module is designed to realize the independent control and continuous adjustment of the bias voltage of each phase shifter unit of the phased array antenna.The center frequency of the antenna is 35 GHz and the overall size is 35mm×50mm×2.5mm.The test results show that the array achieves one-dimensional phase scanning by adjusting the excitation phase of each unit through the power module.The scanning angle is ±20°,and the main lobe gain can reach 5.7dBi.3.The research of K band liquid crystals planar reflectarray based on true time delay is conducted.Aiming at the design concept of planar reflectarray with reconfigurable pattern,a K-band LC-based planar reflectarray and antenna unit based on true time delay technology is designed.The reflection phase is controlled by the delay line structure loaded with liquid crystals,and the radiation of the resonant patch is realized through the slot-coupled feeding.The center frequency of the antenna is 24 GHz.The experimental results show that the reflection phase of the reflectarray can reach 360° and the curve linearity is good.The reflectarray is designed with the above unit,and its aperture size is 75mm×75mm with 100 units.In order to control the change of dielectric constant of liquid crystals by voltage and realize the phase compensation of each unit,a 100-channel adjustable power supply module is designed.The module is realized by FPGA and highvoltage DAC,which can realize DC voltage 0-30 V continuously adjustable,independent and program controlled.The experimental results show that in the frequency range of 22.1GHz-26.1GHz,the 3dB wideband is 16.7%,the maximum gain of main lobe is 20.2dBi,and the maximum scanning angle is ±45°.