Design Of Linear Polarization Converters With Angular Stability Based On Metasurface

Polarization is one of the fundamental properties of electromagnetic waves.Artificially changing and manipulating the polarization direction of electromagnetic waves is beneficial to improving the quality of communication and has important research significance.Polarization converters can controll polarization of electromagnetic waves and are important devices in wireless communication systems.Traditional polarization converters have drawbacks of complex design process,large thicknesses and high requirements for materials and processing processes.In recent years,Metasurface(MS),as a new 2-D planar artificial electromagnetic material,can flexibly control the transmission and polarization of electromagnetic waves,and has the advantages of small spatial dimension,low loss and cost,easy fabrication and integration,so it has also been widely concerned in the field of polarization conversion.Aiming at the increasing demand for polarization conversion rate(PCR),operation bandwidth and angular stability of polarization converters in engineering applications,this thesis proposed a transmissive and a reflective polarization converter respectively based on MS structure.High PCR and angular stability in wide bandwidth are achieved.Additionally,the reflective polarization conversion metasurface(PCM)is applied to planar and conformal surfaces to reduce radar cross section(RCS).The main research of the thesis includes the following aspects.(1)a transmissive dual broadband polarization-insensitive linear cross-polarization converter is designed.A linear cross-polarization converter is designed using four sets of overlapping or orthogonal right-angle triangular pairs of patches.The PCR is higher than95% in the frequency bands of 9.4-13.1 GHz and 13.4-17.2 GHz,and the PCR remains constant when the linear polarization wave is incident at any azimuthal angle.The design can be used in Ku-band satellite communications by performing simulations with CST software and processing tests on the real object.(2)A reflective ultra-broadband linear polarization converter with a wide angle of incidence is designed.The designed polarization converter consists of a pair of "arrow" shaped open resonant ring metasurface units,a dielectric substrate,and a ground plane.Simulation and test results show that the converter achieves over 90% cross-polarization conversion in the 11.5-28.5 GHz band and the PCR remains high with slight bandwidth loss when the oblique incidence varies at range of ±40°.The simulations performed with the CST software and the experimental results are in good agreement,indicating that the design can be used for Ku-and K-band satellite communications.(3)The above designed reflective PCM unit cells are arranged in chessboard-shaped for RCS reduction on planar and conformal surfaces.The phase difference between the PCM and their mirror image cells are 180°,and thus the field will be cancelled and result in RCS reduction.RCS reduction of more than 7 d B can be achieved in the ultra-broadband range of 11.4-29.5 GHz(88.5% relative bandwidth)on planar surfaces,and on cylindrical surfaces within a center angle of 90°,10 d B RCS reduction can also be achieved.The design can be used in modern military areas where stealth technology is needed.