Design And Study Of Broadband Microwave Metamaterial Polarization Converters

As a new type of electromagnetic material,metamaterials are widely used in electromagnetic stealth,electronic countermeasures,satellite communications and other fields by virtue of their physical properties that are different from conventional materials.Polarization is an important property of electromagnetic waves,and the traditional polarization regulation can be realized by natural spin materials,anisotropic crystals and liquid crystal materials.But the polarization regulation devices based on the above materials often have the defects of narrow band width,large size and difficult integration.With the deepening of the research on metamaterials,they are also gradually applied to the field of electromagnetic wave modulation.In this paper,two polarization converters operating in the microwave band are designed,and of which the properties of the polarization converting are researched in detail.The main research content are as follows:(1)A type of metamaterial cross-polarization converter based on dumbbell type unit cell is proposed,and simulation results show that the converter can convert linearly polarized electromagnetic(EM)waves into their orthogonal forms in the frequency range from 13.3 GHz to 24.1 GHz with a polarization conversion rate(PCR)of more than 97%.In addition,it can still maintain a high conversion efficiency in the above mentioned frequency band when the incidence angle increases to45~o.This structure not only has the potential advantages of high efficiency,large bandwidth,and wide incidence angle in the fields of polarization conversion and antenna radiation in microwave frequency range,but also can be extended to terahertz,infrared,and other frequency band.(2)A bifunctional polarization converter based on solid state plasma is designed.When the solid state plasma is in the metallic state,it acts as a reflective linear polarization convertor with a conversion rate of more than 98%in the range of 16.5 GHz to 25 GHz.When the solid state plasma is in the dielectric state,it acts as a transmissive linear-circular polarization convertor with an axial ratio AR<3 d B in the range of 14.7 GHz to 19.4 GHz.Meanwhile,dynamic switching between the two working modes can be achieved by actively changing the conductivity of the solid state plasma without changing the structural parameters.The structure can not only meet the application requirements of different operating modes and different conversion performance,but also has potential applications in communication,sensing and imaging.