Polarization Conversion Metasurfaces And Their Applications In RCS Reduction And Antenna Design

Metasurfaces(MSs),as a type of two-dimensional metamaterials(MMs),have many advantages such as low profile,low losses and easy integration.They have great applications in electronic devices,cloaking,and antenna design.The dissertation will focus on polarization conversion metasurfaces(PCMs)and their applications in radar cross section(RCS)reduction and antenna design.The main contributions are as follows:1.A novel method is proposed to design multi-band multi-functional polarization converters.Three topologies of reflective polarization converters are presented.(1)A broadband and high-efficient polarization converter based on a double-mender-line-shaped resonator is proposed.The polarization converter can convert a linearly polarized(LP)incident electromagnetic(EM)wave(x/y-polarized)into a cross-polarized reflected wave(y/x-polarized).(2)A dual-band multi-functional polarization converter by combing a double-mender-line-shaped resonator and a cut-wire is proposed.The proposed design can convert an LP incident EM wave into an LP reflected wave(LP-to-LP)in the low band and a circularly polarized(CP)reflected wave(LP-to-CP)in the high band,respectively.(3)A triple-band and high-efficient multi-functional polarization converter based on the combination of a split-ring structure and a cut-wire resonator is proposed.The proposed design can achieve wideband LP-to-LP polarization conversion in the first and third bands and LP-to-CP polarization conversion in the second band,respectively.2.Two broadband low-RCS reflecting screens based on checkerboard PCMs are proposed.(1)Based on the standard antenna array theory,we study the scattering characteristics of the one-dimensional structure composed of PCM unit cells and its mirror ones.The numerical analysis demonstrates the relationship between the RCS reduction and the polarization conversion characteristic of the PCM unit cell.(2)Two two-dimensional checkerboard reflecting screens are proposed and investigated based on the one-dimensional one.(3)A broadband PCM unit cell is designed and used to design two checkerboard reflecting screens.Experiments and simulations are in good agreement,which verifies the analysis.3.A wideband CP slot antenna based on PCM is proposed and used to design a wideband,high-gain,and low-RCS CP antenna array.First,a PCM-based superstrate is designed and integrated with a traditional LP slot antenna for wideband CP radiation.The working principle is analyzed based on equivalent circuit model,surface wave propagation theory and full-wave simulation,respectively.Second,a slot array is developed by using four-element antennas and a sequential-rotated feeding network.Concerning the radiation,the array yields a wideband and high gain.Concerning the scattering,the array achievs RCS reduction in both in-band and out-of-band.4.A novel wideband checkerboard-like method for RCS reduction is proposed and applied in the design of CP patch antennas.A wideband high-gain low-RCS CP antenna is presented.First,a novel PCM is proposed.In the low band,the RCS reduction is achieved due to the high-efficient polarization conversion characteristic of the PCM.In the high band,the RCS reduction is achieved due to the 180° phase difference between the PCM and the grounded substrate.The broadband RCS reduction is obtained by combining two different destructive interference principles.Then,the PCM is integrated with a traditional CP patch antenna.An operating bandwidth extension from 4.2% to 15.9% and a gain improvement of 5.55 d B are obtained.Besides,it achieves an over 104% relative bandwidth of more than 6d B RCS reduction.Finally,the method is applied in antenna arrays.