Research And Design Of Reconfigurable Antenna Based On Liquid Metal

With the rapid development of satellite and wireless communication,modern communication systems require the characteristics of large capacity,multi-function,ultra-wideband,etc.,which usually needs several antennas.In order to reduce the size of the system,it is necessary to decrease the number of antennas.Therefore,reconfigurable antennas with the advantages of multi-mode,high efficiency and small size have been widely concerned.At present,radio frequency(RF)devices such as varactor diodes,p-i-n diodes and MEMS switches are widely used to design reconfigurable antennas.These technologies can provide low cost and high reconfigurable speed for antennas.Nonetheless,they have shortcomings in some RF performance metrics(such as the range of frequency tunability,power handling capability and radiation efficiency).Liquid metal EGa In can be used to design reconfigurable antenna due to its fluidity and good conductivity.By controlling the liquid flowing,the structure of the antenna can be changed and consequently the performance can be switched.This new reconfigurable technology overcomes the shortcomings of the traditional RF devices and has the advantages of high linearity,flexibility and conformability.At the same time,wider reconfigurable bandwidth and more reconfigurable states can be obtained with this method.Hence it becomes a research hotspot in reconfigurable technology.Firstly,the research status of liquid metal antenna is introduced in this thesis.Then,on the basis of current technology,a variety of frequency or polarization reconfigurable liquid metal antennas are designed utilizing the various characteristics of EGa In and the basic theory of reconfigurable antenna.The performances of these antennas are verified by fabrication and measurement.The detailed study contents are as follows:(1)A compound frequency and polarization reconfigurable planar monopole antenna and a microstrip quasi-Yagi antenna with continuous reconfigure frequency band and adjustable gain are designed.Firstly,by injecting different amount of EGa In into microfluidic channel etched in PDMS structure to change the resonant length of the planar monopole antenna,its operating band can be reconfigured continuously in the frequency range of 1.43 GHz-9.18GHz.Then,by introducing rectangular circular channels on both sides and injecting EGa In as parasitic strips,the antenna realizes a tunable frequency band of 1.4 GHz-4.4 GHz with LP and the reconfiguration among three states of LP,LHCP and RHCP.On the other hand,EGa In is used as the driven dipole arms and director of microstrip quasi-Yagi antenna.By changing the length of EGa In in the channels,the operating band of the proposed antenna can be continuously tuned in the frequency range of 1.79 GHz-4.8 GHz and the gain can be adjusted in each state.(2)Two compound frequency and polarization reconfigurable square slot antennas are designed.First of all,the PDMS structure with microfluidic channels along the direction of+45~?and-45~?with respect to the x-axis is loaded on the slot.Each direction contains five channels with three different lengths.The proposed antenna realizes the reconfiguration among three states of LP,LHCP,and RHCP.Moreover,the working frequency in CP states can be reconfigured among three bands.The 3 d B axial ratio band(ARBW)of each CP state is 26.42%(2.3 GHz-3 GHz).Then,on the basis of this structure,the microfluidic channels are changed into the shape of multiple cylindrical chambers connected with each other,so that the length of EGa In can be directly controlled in one channel.This structure only has two channels in the direction of+45~?and-45~?with respect to the x-axis,which simplifies the antenna structure.At the same time,the reconfigurable frequency states in each CP state are increased to five,and the 3 d B ARBW is also significantly broadened.(3)A polarization reconfigurable metasurfaced antenna is designed.The PDMS coating is loaded above the microstrip slot antenna,which contains two-layer microfluidic channels for the conversion between LP and CP states.Injection of the upper channel constitutes the LP-to-LHCP polarization conversion metasurface,and injection of the lower channel constitutes the LP-to-RHCP polarization conversion metasurface.When EGa In is not injected,the antenna works in LP state.Therefore,the reconfiguration of the proposed antenna among LP,LHCP and RHCP states is realized by changing the injection of the metasurface structure.The central frequencies of the three states are 2.52 GHz,2.61 GHz and 2.6 GHz respectively,and the peak gain of the antenna is higher than 6.4 d Bi.