| Modern intelligent systems rely on the propagation of electromagnetic waves for information exchange,and the characteristics of electromagnetic waves can directly affect the communication quality between systems.In order to enhance the stability of signal transmission in practical applications,it is necessary to effectively regulate the various parameters of electromagnetic waves manually.Metamaterials utilize artificially designed special unit structures to effectively regulate engineering indicators such as the radiation direction,frequency,amplitude and phase of electromagnetic waves.If only the periodic arrangement of metamaterials on a plane is allowed,a metasurface is formed.As a dimensionality reducing derivative of metamaterials,metasurface have become a very popular research direction in recent years due to their simple structure and low cost advantages in applications.This thesis conducts theoretical derivation,unit simulation,performance analysis,and experimental verification through the research and exploration of a new type of metasurface,and designs two high-performance transmission type linear circular polarization conversion surfaces and a broadband stacked frequency selective surface.The main work is divided into the following three aspects.1.A multi-layer transmission line circular polarization conversion surface based on flexible material substrate is proposed to address the issues of high loss and high cost in general transmission polarization converters.The metasurface operates in the 60-64 GHz millimeter wave frequency band.By introducing rectangular patches with different sizes in different directions,the incident linearly polarized waves can be effectively converted into circularly polarized waves for transmission.The average surface transmittance obtained by software simulation reaches 85%,and the axial ratio of the transmitted circularly polarized waves within the working bandwidth is less than 3d B.By using flexible polyimide materials,the processing cost has been greatly reduced,which has important engineering significance in millimeter wave imaging,radar communication and other fields.2.A hard substrate transmissive linear circular polarization converter is proposed to address the impact of surface height errors on the performance of flexible metastructures.This super structured surface is a single dielectric double-sided plate,which can achieve linear circularly polarized electromagnetic wave conversion within 54 to 64 GHz without the need for a layered structure.Through software simulation,while ensuring the conversion efficiency of circularly polarized waves,the average transmittance is further improved to 90%.At the same time,the conversion performance of the surface at a 40 degree inclination angle of the incident wave is still excellent,greatly improving the stability of the surface during use.Finally,the processing verification of the linear circular polarization converter was carried out,and the correctness of the design was demonstrated through analysis of the difference in imaging signal-to-noise ratio.3.A broadband layered frequency selective surface based on metamaterials is proposed to meet the requirements of astronomical systems for wideband reception of reflected signals.The metasurface utilizes the design concept of low-pass filters,and the lumped components are equivalent to surface metal,with a passband in the 20-47 GHz frequency band and a stopband in the 80-115 GHz frequency band.The passband reflection coefficient is less than-20 d B,and the stopband transmission coefficient is less than-40 d B.The patch adopts a square structure so that it can have the same effect on the electromagnetic waves incident in two orthogonal directions.The common flexible polyimide material is selected as the substrate,which reduces the processing difficulty and cost.The surface still meets the engineering requirements when the incidence angle is greater than 50 degrees,and can be applied to radio astronomical communication systems. |
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