Tunable Microwave Passive Devices Based On Liquid Crystal Technology

For the increasing demand of portable devices and continuous tunable devices,tunable microwave passive devices become more and more popular.Liquid crystal with low loss and continuous adjustable characteristics is a tunable material.Compared with other tunable materials,liquid crystal can continue to work at a lower bias voltage or low dielectric constant.Therefore,it is often applied to the design of tunable passive devices.In this paper,based on the tunable dielectric properties of liquid crystal materials,microstrip filters,microstrip leaky wave antennas,and array antennas based on liquid crystal are designed and fabricated.The specific research content is as follows:Firstly,two types of tunable microstrip filters based on liquid crystal are designed.They use ring structure and square structure respectively.When the dielectric properties of the liquid crystal change,the filter can achieve continuous tunable performance.When analyzing the principle of the ring filter,it can be seen that the position of the transmission zero outside the passband is shifted when the size of the disturbance region change.The liquid crystal material is located below the position of the disturbance zone.When its dielectric properties change,the transmission zero position can shift at the same time.The tunable ring filter uses three methods of feed through vias feed,without vias feed and CPWs feed.The CPW feed is the way to maximize the transmission zero offset of the ring filter and has less impact on the performance of the dual mode ring filter.In addition,slotted lines are implemented on the surface to realize different performances of microstrip square filter.Three-mode and dual-mode dual-passbands microstrip square filter are designed.When the dielectric properties of the liquid crystal change,the passband of the filter shifts.Among them,the first passband in the dual-mode dual-band bandpass tunable filter does not have obvious frequency offset,and the second passband completes obvious frequency offset.Secondly,tunable leaky wave antennas based on liquid crystal material are designed.When the dielectric properties of the liquid crystal change,Leaky wave antenna can complete fixed-frequency beam scanning.Four kinds of leaky wave antenna based on composite left and right hand structures are proposed:5 cell asymmetric structure microwave leaky wave antenna,10 cell asymmetric structure microwave leaky wave antenna,10 cell symmetrical structure I microwave leaky wave antenna and 10 cell symmetrical structure II microwave leaky wave antenna.Comparing the simulation results with the measured results,it is found that when the dielectric properties of the liquid crystal change,the 10-cell symmetric structure 11 tunable leaky wave antenna has the largest beam scanning range.Thirdly,two types of array antennas based on liquid crystal materials are designed.When the dielectric properties of the liquid crystal change,they can complete fixed-frequency beam scanning.The cell of rectangular array antenna is composed of a reflective phase shifter and a rectangular antenna.The slot array antenna is composed of slot antennas and a feed network which is made up of meander line phase shifters.When the dielectric properties of the liquid crystal change,the achieved beam scanning range of the slot array antenna is larger than the achieved beam scanning range of the rectangular array antenna.