Research On Reconfigurable Passive Devices Based On Liquid Crystal Materials

As a tunable medium with dielectric anisotropy,liquid crystal materials have the advantages of low tuning voltage,integrating circuit substrate easily and linear continuous adjustment.Its application in microwave passive devices can realize the reconfigurable properties of passive devices,and can meet the needs of passive devices with multi-function,low cost and easy integration in modern communication systems.Therefore,this thesis studies the reconfigurable passive devices based on liquid crystal materials.The research work of this thesis mainly includes:1.Based on the liquid crystal electrical tuning theory,two broadband frequency reconfigurable filters were designed respectively.One of them works in the C-band.By designing a multimode resonator loaded with a branch in the center and a coupled feed structure to construct three resonance points,the design of a band-pass reconfigurable filter design is realized.the experimental results show that the filter center frequency is 5.2GHz and its bandwidth is 2.8GHz.the reconfigurable range of the filter frequency response during the voltage increasing is 15%.Within the tuning range,the return loss value is greater than 10 dB,and its insertion loss is about 5dB.The other works in the Ka-band,by loading branches on the ring resonator and introducing in-loop capacitors to construct three transmission zeros to achieve millimeter wave tunable bandpass filter design.The experimental results show that the center frequency of the filter is 40 GHz and the bandwidth is 10 GHz.The tuning range of the filter during the voltage increase is 1.6GHz.During the tuning process,the insertion loss in the filter band is about 5.5dB,and the return loss is greater than 9dB within the tuning range.2.Based on the slot coupling principle and the liquid crystal tuning mechanism,a liquid crystal coded switching antenna is designed,and its different coding states can correspond to different antenna radiation patterns.Firstly,a radiation controllable unit based on adjustable frequency is designed by using the principle of slot coupling and liquid crystal tuning,and then it is formed into a 5-cell series-fed array.Apply voltages of 0V and 10 V to the cell bias circuit through the voltage source to achieve controllable cell radiation in the array,thereby generating coding states of 1 and 0,and simulation tests of four typical coding states of the cross-fed array are conducted to verify the feasibility of the liquid crystal coding switch antenna.3.Based on the liquid crystal tuning mechanism and LTCC technology,a millimeter wave liquid crystal phased array antenna is designed.First,a liquid crystal phase shifter with a 360-degree phase shift and a high-gain phased array radiation unit are designed,and then the overall simulation design of the LTCC technology is considered,including the design of the same layer transition circuit and DC blocking in the capacitor design.the beam scanning results were evaluated and analyzed,and the simulation results were roughly the same as the expected calculation results.The application value of the liquid crystal circuit in the LTCC technology is expanded.