| As a type of electromagnetic metametasurface,a polarization conversion metasurface can achieve arbitrary control over the polarization of electromagnetic waves.The polarization conversion metasurface is a two-dimensional plane composed of periodic units.Compared with traditional three-dimensional metamaterial structures,it has the advantages of low profile,low loss,and easy integration with antennas.With the rapid development of wireless communication systems,radar navigation,and stealth technology,the complexity and multitasking mode of communication systems continue to increase,and the requirements for antennas are becoming increasingly demanding.In the increasingly complex application context,traditional antennas often cannot meet the requirements of high complexity and multitasking mode.Antennas loaded with polarization conversion metasurfaces have the advantages of diverse polarization modes,easy integration,high efficiency,and low radar cross-section,and can be better applied in complex communication systems.This thesis mainly studies the design and application of polarization conversion metasurfaces,The main contents of this thesis are as follows:Research and analysis were conducted on the design principles of polarization conversion surfaces,and two types of linear circular polarization conversion surfaces were designed based on the basic principles.The first polarization conversion metasurface achieved broadband linecircular polarization conversion in the frequency range of 9.85-21.0 GHz.The polarization conversion metasurface was loaded on top of a microstrip antenna,and in the frequency ranges of 11.1-14.7 GHz and 16.3-17.5 GHz,it converted the linearly polarized waves radiated by the feed antenna into circularly polarized waves,verifying the polarization conversion performance of the conversion metasurface.The second design was a multi-layer polarization conversion metasurface.The polarization conversion metasurface had linear-circular polarization conversion characteristics in the frequency range of 3.1-5.3 GHz and cross-polarization conversion characteristics in the frequency range of 6.5-9.1 GHz,achieving a structure design with dual polarization conversion modes.Then,a cross-polarization conversion unit was designed.The designed unit structure can convert incident waves to cross-polarization direction in the frequency range of 5.4-11.0 GHz,and the polarization conversion rate is greater than 94%,achieving the design of a broadband and high conversion rate polarization conversion unit.Secondly,based on the polarization conversion metasurface and using the phase cancellation principle,the cross-polarization units were arranged in a checkerboard pattern in a mirror-symmetric manner,constructing an RCS reduction metasurface.Compared with a PEC plate of the same area,the minimum RCS reduction effect of the RCS reduction metasurface was more than 5 d B higher,and the maximum reduction reached 34 d B.Finally,a low RCS antenna was designed by loading the RCS reduction metasurface on a microstrip antenna,which has broadband and low RCS characteristics.When the antenna is loaded,the reduction of metasurface RCS is greater than10 d B compared with that without loading.This thesis conducts simulation analysis on line-circular polarization conversion metasurfaces and cross-polarization conversion metasurfaces.Based on the line-circular polarization conversion unit,it realizes the conversion of linearly polarized antennas to circularly polarized antennas,and based on the cross-polarization conversion unit,it achieves RCS reduction of antennas.providing new design ideas for circularly polarized antenna design and reducing antenna RCS.The research content of this thesis has important reference value in the design of broadband,high-efficiency,and multi-mode polarization conversion metasurfaces,as well as the application of polarization conversion metasurfaces in antenna systems. |
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