Research On Wideband RCS Reduction Based On Electromagnetic Metasurface

Due to the development of radar technology,the technologies pose an urgent threat to the survivability of the stealth targets.In order to improve the stealth performance of the target,the most important index that we use to measure the stealth performance of the target is the radar cross section(RCS).Lower RCS means better stealth performance.Recently,with scientific and technological development,many researchers have started to use electromagnetic metasurface to reduce target's the radar cross section and to improve their stealth properties.However,there are still some problems in existing work,such as narrow band,low efficiency and single function.For the purpose of improving electromagnetic metasurface's working performance,the principles of metamaterial absorbers and polarization conversion metasurface are analyzed in this thesis.A highly efficient wide-band metamaterial absorber is then proposed with optical transparency characteristics and a lowprofile broadband polarization conversion metasurface,respectively.The coding polarization conversion metasurface is then proposed,which realizes the flexible regulation of scattering pattern and the optimization of the metasurface performance.After polarization conversion metasurface being used to combine with the patch antenna,the RCS of the antenna is effectively reduced without affecting the antenna radiation.The thesis mainly covers three parts listed below:1.In order to improve the absorption rate of the metasurface absorber and to achieve the transparent design of the whole structure,this thesis proposes a highly efficient broadband metasurface absorber with optical transparency based on the new resistive films.The metal pattern on dielectric substrate is replaced by plastic substrate and ITO films.Because of the good loss characteristics,the resistive films can improve the absorption rate of the absorber during the whole band.Simulation results show that the absorber achieves the bandwidth of4.92-24.55GHz(131% relative bandwidth)and 5.74-21.85 GHz(115% relative bandwidth)for 90% and 95% absorption rate respectively.It can maintain an 80% absorption rate in the whole band when the incident angle is tilted to 50°.2.To solve the problem of complex structure and high profile of the metasurface,a singlelayer low-profile polarization conversion metasurface is proposed.The single-layer structure of the metasurface unit makes the low-profile characteristic of the overall structure.By using two metallic vias connecting the metasurface and metallic ground,the metasurface achieves the bandwidth of 9.55-27.35 GHz with PCR>90% under the condition with the structure being only 0.08?.Moreover,the polarization conversion metasurface unit is used to the coding design: By superimposing different coding arrangements based on the idea of convolution,the coding polarization conversion metasurface realizes the rotation and shifting of the scattering beams.The simulated annealing algorithm is used to optimize the monostatic RCS reduction,and the RCS reduction of the optimized metasurface increases2.7d B in the 8-20 GHz compared to the chessboard metasurface.The scattering pattern of the optimized metasurface achieves diffuse feature within the upper half space.3.In order to solve difficulties for the metasurface to give consideration to both the radiation and the scattering of the antenna.Based on the low-profile polarization conversion metasurface mentioned above,combining the unit of the PCM and patch antenna,the unit and antenna have the same profile and share same metallic ground.The proposed antenna achieves integrated design with the patch antenna and PCM.The simulation results suggest that the structure of polarization conversion metasurface doesn't affect antenna's radiation performance.Also,the proposed antenna based on the low-profile polarization conversion metasurface achieves the RCS reduction with the average monostatic RCS reduction of 10 d B within the 9.5-27 GHz range.Besides,the proposed antenna can achieve above 6d B wideband average bistatic RCS reduction when the incident angle is tilted to 30°.