| The manipulation of electromagnetic(EM)waves is extensively applied imaging microscopy,optical sensing,molecular biotechnology and microwave communication,which has attracted close concern from scientific community.Traditional approaches of controlling EM wave polarization,such as optical activity of crystals,birefringence effect of anisotropic materials,Faraday effect,proteins with helical secondary structures,and chiral liquid crystals.However,the polarization converter realized by the above methos has the drawbacks of large volume,narrow bandwidth,sensitive incidence angle and high processing cost.Therefore,it is of great significance to realize the requirement of micro-polarization controller with broadband and angle insensitivity by relying on artificial structures.Metasurface,has excellent optical and electrical properties,is widely applied in the manipulation of EM wave polarization state.Nowadays,the polarization converter based on metasurface exists the disadvantages of single polarization mode,single frequency band,poor polarization conversion performance,narrow relative bandwidth,and poor oblique incidence characteristics.Based on the above problems,this paper designs a rigid and reflective dual-polarization conversion metasurface,a flexible,dynamic regulated and reflective dual-polarization conversion metasurface and a rigid and transmissive dual-broadband polarization conversion metasurface.The specific research contents of this paper are as follows:In accordance with the shortcomings of single polarization mode and poor polarization performance of most reflective metasurfaces,a rigid and reflective dual-polarization conversion metasurface is constructed by CST microwave studio,which achieves highefficiency linear polarization conversion and circular polarization conversion.The simulation results show that the polarization conversion ratio(PCR)is higher than 90 % in the frequency range of 6.85-11.05 GHz and the corresponding relative bandwidth is 47.15%.The axial ratio(AR)is less than 3 d B in the frequency range of 5.83-6.68 GHz and 11.54-16.93 GHz,and the corresponding relative bandwidths are 13.59% and 37.86%,respectively.The excellent polarization conversion performance is maintained within the incident angle of 50°.The designed rigid and reflective dual-polarization conversion metasurface has the deficiencies of inflexibility and non-dynamic regulation.The structure optimization and material optimization based on rigid and reflective dual-polarization conversion metasurface are carried out.The dielectric material of FR-4 is substituted by the flexible material polyvinyl chloride(PVC),and the graphene material is added to realize flexible and dynamically adjustable performance.The simulation results show that the incident wave is converted into the cross-polarized wave in the frequency range of 7.47-12.38 GHz covering the X-band,and the corresponding relative bandwidth is 49.47%.The incident wave is converted into the circular polarized wave in the frequency range of 6.25-7.25 GHz and13.00-26.68 GHz covering the C,Ku and K bands,and the corresponding relative bandwidths are 14.81% and 68.95%,respectively.The linear polarization conversion performance and circular polarization conversion performance of the optimized structure are promoted.In addition,the dynamically adjustable characteristic of graphene is analyzed.The dynamic regulation of PCR and AR are obtained by modifying the applied bias voltage to control its Fermi level.Aiming at the disadvantages of single-band and poor polarization conversion performance of most transmissive metasurfaces,a rigid and transmissive dual-broadband polarization conversion metasurface is constructed by CST microwave studio.The proposed metasurface has asymmetric transmission characteristics,which is composed of two orthogonal metal gratings,metal resonator and FR-4 dielectric spacer.The simulated results show that the designed metasurface can convert x-polarized incident waves into y-polarized waves in the frequency ranges of 4.64-14.37 GHz and 17.02-37.23 GHz,and the corresponding PCR exceeds 90%.The relative bandwidths of the two bands are 102.37% and74.51%,respectively.The excellent performance of dual-broadband and high-efficiency covers C,X,Ku,K and Ka bands,which can also be well maintained in the oblique incidence range of 0-50°.In addition,a 15×15 metasurface model was fabricated and tested.The experimental results show that the PCR is greater than 90% in the frequency range of4.90-14.33 GHz and 17.11-37.13 GHz,and the relative bandwidth is 98.08% and 73.82%,respectively.The experiment and simulated results are basically in good agreement with each other. |
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