Research On Reconfigurabe Antenna With Electrically Controllable Beam Based On Liquid Crystals

Modern communication systems have a strong demand for reconfigurable antennas with electrically controllable beam,low profile,low cost and easy integration.In recent years,reconfigurable leaky-wave antenna and reconfigurable holographic antenna have been proposed to realize low-cost,low-profile beam reconfigurable antenna.These antennas employ tunable medium such as diode,ferrite,liquid crystal to change the phase or amplitude of antenna element,realize beam scanning,and effectively reduce the profile and cost of antenna.Liquid crystal is a kind of dielectric constant tunable material,compared with diodes,liquid crystal has a higher working frequency,compared with ferrite,liquid crystal has a lower loss and is easier to control.In this dissertation,liquid crystal is employed to study the reconfigurable antenna with electrically controllable beam.In view of many problems faced in design,theoretical solutions and design methods are proposed,and a series of novel reconfigurable antennas with electrically controllable beam based liquid crystal are designed.These works lay a foundation for the engineering application of reconfigurable antenna with electrically controllable beam based on liquid crystal.In order to enlarge the beam scanning range of liquid crystal based reconfigurable composite right/left-handed leaky-wave antenna,two theoretical approaches are proposed.Through control the distribute parameters harmonically,the stop band and deterioration of broadside radiation performance during beam scanning is well suppressed.Based on the proposed methods,the first reconfigurable composite right/left-hand leaky-wave antenna without stop band liquid crystal is designed in this dissertation.A large electrically controllable beam scanning range is obtained and a good broadside radiation performance is achieved.The dispersion equivalent circuit model of extended composite right/left handed transmission line is established.Based on the model,the operating characteristics of dual-band metamaterial leaky wave antenna are analyzed,and the control methods of frequency spectrum position and frequency interval for two operating bands are proposed.Based on the analysis of frequency response characteristics for resonant circuits and parallel stubs of transmission line,the design method for low profile,compact dual band reconfigurable metamaterial leaky wave antenna based on liquid crystal is proposed,and the backward to forward electrically controllable beam scanning is realized in both working bands.The radiation principle of reconfigurable holographic antenna is explained for based on the theory of leaky wave antenna,and the mathematical model of array factor for reconfigurable holographic antenna is established.Based on the model,the effects of on-to-off ratio of element and modulation phase delay between contiguous elements on the radiation performance of reconfigurable holographic antenna are studied.A method to reduce the sidelobe level of reconfigurable holographic antenna by increasing the on-to-off ratio of element is proposed,and a novel reconfigurable holographic antenna based on liquid crystal is designed with large beam scanning range and low initial sidelobe level.The phase center fluctuation of reconfigurable holographic antenna during beam scanning determines the accuracy of positioning system.An improved holographic strategy is proposed to well suppress the phase center fluctuation caused by the transmission attenuation,mutual coupling between elements and phase disturbance caused by reconfigurable elements.By applying the improved holographic strategy to the liquid crystal based reconfigurable holographic antenna proposed in this dissertation and literature,the phase center fluctuation during beam scanning is obviously reduced,and the stability of the phase center is greatly improved.Aiming at solving the practical problems in the design of liquid crystal-based beam reconfigurable antenna,this dissertation theoretically explores the root causes of the problems,gives the theoretical solutions and effective design methods,and verifies them by the theoretical analysis,simulation optimization and experimental testing.The contents of dissertation promote the application processing of beam reconfigurable antenna based on liquid crystal in modern communication system.