Design Of Reconfigurable Antenna Based On Liquid Metal

With the rapid development of modern radar and communication systems,the electromagnetic space is increasingly complex,and the requirements of various military/civilian platform antenna systems are enhanced.However,the limited space of platform requires integration of multi-functional antenna systems.Based on the above demands,reconfigurable antennas which have multiple radiation functions with a single antenna structure,becomes a better solution to meet the above challenges,and received a lot of attention in recent years.The available reconfigurable technologies realize the adjustment of antenna frequency,polarization,pattern and other radiation functions.And it has the advantages of reducing the number of system antennas and decreasing the system size.The current reconfigurable technology mainly adopts active devices: varactor diodes,PIN diodes,RF MEMS switches,etc.These devices not only provide high reconfigurable speed and accurate control of antennas,but also have certain limitations,such as low power capacity,complex bias circuits required for large-scale applications,and few reconfigurable modes.Liquid metal can be used as a switch or radiator benefited by its fluidity and good conductivity at room temperature.The antenna radiation performance can be adjusted by changing the liquid metal.More over,the application of liquid metal overcomes the shortcomings of low power capacity and few reconfigurable modes of traditional electronic switching devices.This thesis first investigates the development of liquid metal applications in reconfigurable antennas,then combines the physicochemical properties of liquid metal and the problems that need to be solved at present to design a variety of liquid metal antennas with reconfigurable frequency,reconfigurable frequency and polarization,and reconfigurable pattern.Finally,prototypes of proposed antennas have been fabricated and measured.Specific work schedule:(1)A tunable frequency dual-loop antenna and a continuous tunable frequency dual splitloop antenna are presented in chapter 3.The first antenna is designed in PMMA with two annular channels.Fill or discharge the liquid metal into the channels by pressure,realizing the frequency between low frequency mode(2.0～2.03GHz),high frequency mode(3.38～3.46GHz),and dual frequency mode(2.01～2.04 GHz,3.47～3.55GHz).On the basis of the previous work,the second antenna adopts a split annular structure and optimizes the position of the feeding structure to excite a new resonance frequency.By driving the movement of liquid metal in the channel,not only the frequencies between the single frequency mode(3.5GHz),dual frequency mode(2.08 GHz,3.11GHz),and triple frequency mode(2.09 GHz,3.12 GHz,3.58GHz)are realized,but also the frequency of 2.08～4.7GHz is continuously adjustable.(2)A frequency-polarization reconfigurable dual split-loop antenna is designed in chapter 4.On the basis of the above antennas,the linear polarization reconfigurability is added.The antenna utilizes liquid metal as a RF switch.By filling and discharging liquid metal in four channels,the on or off state of solid metal can be controled.Finally the antenna realizes reconfiguration between eight reconfigurable states.The simulation and measurement results show that the antenna achieves x polarization and y polarization in low frequency mode(2.09～2.12GHz)and high frequency mode(3.53～3.61GHz)as well as any combination of x polarization and y polarization in dual frequency mode(2.10～2.13 GHz,3.56～3.63GHz).(3)A Vivaldi antenna with reconfigurable pattern and a one-dimensional reflector array antenna with adjustable beam direction are presented in chapter 5.Vivaldi antenna as an ultra-wideband antenna with exponential slot line and larger plane makes liquid metal difficult to fill.Four identical Vivaldi units are arranged at 90° intervals along the horizontal plane with the origin as the center,and the flow channel design is carried out.By driving the liquid metal to fill one cell at a time,reconfigurability in four directions is achieved.Based on the fluidity of liquid metal at room temperature,the second antenna controls the height of the short-circuit surface in the waveguide unit by injecting or discharging liquid metal.Hence the reflection phase of the reflected wave reaching the antenna aperture can be changed,and the array realizes the H-plane ±23° beam scanning.