Investigations Of Electromagnetic Space Security Based On Digital Coding Metasurface

Digital coding metasurface uses the discrete digital states to characterize the electromagnetic(EM)characteristics,which greatly simplifies the design process of metasurfaces,builds a bridge between the physical world and the digital world,and also provides a new perspective for researchers to design and study metasurfaces.Digital coding metasurface is capable of powerfully and flexibly manipulating EM wave,which shows its great research value and application prospect in the field of EM space security.Taking the digital coding metasurface as the research object,this thesis has carried out a series of research on its applications in the field of EM space security.The research content is mainly divided into the following aspects:(1)Investigating the phase quantization effects on the beam scanning performance of coding metasurface.In this work,coding metasurfaces with different bit precision at 9.05 GHz are designed and analyzed.The significant influence of phase quantization error on gain and sidelobe level is revealed through theoretical analysis and simulation verification.Then,an innovative method is proposed to reduce the phase quantization error and thus improve the main lobe gain.Finally,simulation results show that,under vertical incidence of 9.05 GHz spherical wave,the main lobe gain achieves gain improvement of 1.58 d Bi.The measured results are consistent with the simulated ones,which verifies the feasibility of improving the gain of the reflectarray antenna from the dimension of phase quantization error.(2)Combining computer vision with digital coding metasurface,a real-time adaptive metasurface prototype with EM wave "tracking" ability is realized.In this work,the machine learning open source library Open Pose is used to realize the real-time monitoring of human posture.For the detected specific human posture,the designed adaptive metasurface will correspondingly make actions such as beam orientation.In order to obtain the target position required by beam orientation,it is realized by monocular ranging or binocular ranging based on Open CV.(3)Based on the coding metasurface,the RCS(Radar Cross Section)reduction technology is researched.Firstly,the monostatic and bistatic RCS reduction capabilities of random coding metasurface and BPSO(Binary Particle Swarm Optimization)optimized coding metasurface are compared,which shows the feasibility and efficiency of BPSO algorithm in optimizing the design of low scattering coding metasurface.Then,a 2-bit coding metasurface based on polarization conversion is designed.After BPSO optimization,the designed coding metasurface realizes more than 10 d B monostatic RCS reduction in the 24GHz-43 GHz frequency band,and also keeps a good performance of bistatic RCS reduction.