Design Of Reconfigurable/High-Efficiency Polarization Conversion Metasurfaces And Their Application

In recent years,wireless communication systems have played an increasingly important role in the military and civilian fields,and antennas,as front-ends in wireless communication systems,directly determine the performance of the entire system.However,limited by the antenna theory and technology,antennas with traditional structures are difficult to have multiple good performances or have multiple functions at the same time.Electromagnetic metasurface has attracted extensive attention and research in the scientific community due to its unique electromagnetic properties,and provides new design ideas and research directions for microwave radio frequency devices such as antennas.The antenna is a special scattering structure that simultaneously scatters electromagnetic waves and radiates electromagnetic waves.The conventional radar cross-section(RCS)reduction method reduces the radiation performance of the antenna and also significantly degrades the radiation performance of the antenna.The introduction of the electromagnetic metasurface into the antenna can effectively reduce the RCS of the antenna in a wide frequency band while the radiation performance of the antenna will not be affected.The focus of this paper is on the electromagnetic metasurface design for the antenna RCS reduction.The reconfigurable and high-performance polarization conversion metasurfaces are designed respectively,and the two metasurfaces are respectively applied to the reduction of the antenna RCS through the integrated design.The main contents of this thesis include:(1)A reconfigurable polarization conversion metasurface based on PIN diode is proposed.The reconfigurable polarization conversion metasurface can be switched between the polarization conversion mode and the reflection mode by loading of PIN diodes.In the polarization conversion mode,the reconfigurable polarization conversion metasurface can rotate the polarization direction of the incident electromagnetic wave by 90°.In the reflection mode,the reconfigurable polarization conversion metasurface can exhibit a total reflection characteristic similar to a metal plate.The bias lines with chip inductors at both ends enable simultaneous control of all PIN diodes without affecting the polarization conversion performance of metasurface.In addition,the physical mechanism and equivalent circuit of the reconfigurable polarization conversion metasurface are analyzed.(2)A broadband and high-efficiency polarization conversion metasurface based on 2.5-D structure is proposed.The two-layer split structure and the 2.5-D metal strip greatly increase the polarization conversion rate in the entire operating frequency band while expanding the polarization conversion bandwidth.The 2.5-D polarization conversion metasurface can effectively rotate the polarization direction of the x-polarized or y-polarized incident electromagnetic wave to its cross-polarization direction,and its polarization conversion ratio is greater than 96% in the relative bandwidth of 99.5%.The typical parameters of the metasurface are analyzed by simulation.The simulation results show that the designed polarization conversion metasurface can be applied to planar antennas with different types,sizes or profiles.(3)The application of polarization conversion metasurface in antenna is studied.Through the analysis and the integrated design,the above two polarization conversion metasurfaces are respectively applied to the design of the printed dipole antenna and the circularly polarized microstrip antenna.The printed dipole antenna can be switched between the low RCS mode and the operating mode via PIN diodes.In the operating mode,the radiation performance of the antenna is not degraded compared to the reference antenna.In the low RCS mode,the RCS of the antenna is effectively reduced in the wideband.The circularly polarized microstrip antenna based on 2.5-D polarization conversion metasurface realizes the reduction of single-station RCS and dual-station RCS in a wide frequency band under the premise that the radiation characteristics are not affected by the coating structure of the metasurface.The average reduction of single-station RCS in the 4-15 GHz band is 12.97 dB.