Design Of Circularly Polarized Metasurface Antenna Based On Characteristic Mode Theory

With the application of 5G technology and large-scale integrated circuit technology in wireless communication systems,antennas,as an important part of wireless communication systems,need to meet users' requirements for high transmission rate,communication quality,and lightweight electronic equipment.Compared with linearly polarized antennas,circularly polarized antennas can resist multipath interference,reduce the influence of polarization distortion,and improve the efficiency and stability of communication systems.Applying the metasurface that can flexibly control electromagnetic waves to the design of circularly polarized antennas can add to the antenna performance while retaining the advantages of circularly polarized antennas.Therefore,it is of great value to carry out research on circularly polarized metasurface antennas.Through the characteristic mode theory,the working mechanism of the antenna can be clearly grasped under the passive condition,thereby reducing the blindness of the antenna design.In view of the guiding role of the characteristic mode theory,this paper analyzes the metasurface by using the characteristic mode theory and designs circularly polarized metasurface antennas with broadband and miniaturization characteristics on this basis.The research work is as follows:1.A broadband circularly polarized metasurface antenna operating in the C-band is designed by the characteristic mode theory.Firstly,through the reflection characteristics of periodic metasurface units,the influence of unit width,unit spacing and dielectric substrate thickness on the resonant frequency of the antenna is grasped,and the size of the metasurface unit is preliminarily determined.Then,the evolution process of the metasurface is analyzed using the characteristic mode theory,and the antenna performance is also predicted while explaining the circular polarization principle of the designed antenna.In the process of designing the feed structure to excite the two target modes,combined with the characteristic mode analysis and the floor current distribution,it is found that by rotating the gap on the floor by a certain angle,the modal significance of the middle frequency band of the two modes can be effectively improved,thereby expanding the axial ratio.bandwidth.This mode compensation method provides a new idea for the design of wide circularly polarized antennas.Finally,the antenna achieves a relative impedance bandwidth of 31.4% and a relative axial ratio bandwidth of 17.1%.The measured results,simulation results and theoretical analysis results of the antenna are basically consistent.2.A small circularly polarized metasurface antenna is designed based on the characteristic mode theory.By comparing the reflection coefficients of several metasurface elements,a miniaturized metasurface element structure with symmetrically loaded branches along the x-axis and y-axis is proposed.The circular polarization performance of the antenna is analyzed through the characteristic mode theory and the influence of the loading stub length on the mode frequency and phase difference is explored.Then,the performance of the three miniaturized metasurface antennas was compared,and the branch loading mode of the metasurface unit was further determined.Without sacrificing the antenna gain performance,the antenna has a-10 d B impedance bandwidth of 26.7% and a 3d B axial ratio bandwidth of11.3%.Compared with the unloaded metasurface antenna,the electrical size is reduced by32%.In addition,the antenna was processed and measured,and the measured results and simulation results of the antenna showed good consistency.