Research Of Polarization Converter And Its Application Based On Metasurface

Polarization converter is a kind of polarization control device which can effectively manipulate the polarization state of electromagnetic(EM)wave,and it has been widely used in the design of microwave,millimeter wave and nano photonic devices.However,traditional polarization control devices has a relative complex design process,and it also has high requirements on the material and processing technology.Metasurface(MS),a two-dimensional composite electromagnetic material composed of periodic or aperiodic artificial structures,which can realize the regulation of amplitude and phase through the different structure unit,so as to achieve the control of the electromagnetic wave polarization,which greatly reduced the difficulty of the design and processing.In order to solve the problems like bandwidth and multi-polarization conversion of polarization converter,the reflectionand transmission-type polarization converter based on metasurface are proposed,which can manipulate the different polarization of electromagnetic wave independently by optimizing the metasurface unit sturcture.On this basis,polarization converter metasurface is combined with antenna design,which provides a new approach for circular-polarized antenna design.The main research includes the following aspects:(1)First of all,the polarization converter based on reflective metasurface is proposed,and its working principle is studied using interference theory.An asymmetrical cross rectangular ring is loaded around the asymmetrical cross rectangular patch to design a reflective metasurface,which can efficiently convert the linear-polarized incident wave into circular-polarized reflected wave within frequency band of 13.2-21.4 GHz.Further,a multi-polarization conversion metasurface is designed composed of two L-shaped patches with different sizes,which can achieve three different polarization conversion functions within frequency band of 5.5-22.75 GHz.The design plays an important role for the construction of multi-function polarization switching device and has extensive application prospect in the fields of radome,remote sensors and radiometer.(2)In the practical engineering application,the shadowing effect of radiation source is an inevitable problem for reflective metasueface.Therefore the transmission-type polarization converter based on metasurface is studied in this chapter.First of all,we explain the working principle of transmission polarization control.Secondly,on the basis of the square patch with truncated corners,a transmission-type polarization converter is designed composed of a fan-shaped patch structure.Due to the anisotropy of the proposed structure,the linear-polarized incident wave is converted into right handed circular-polarized wave within the band of 4.4-7.7GHz,3-dB relative axial ratio bandwidth is 54%.Further,a cylindrical metal via is utilized to connected the upper and lower patches,which composes a 2.5-dimension metasurface and 3-dB relative axial ratio bandwidth is broadened to 64%.(3)At last,a novel circular-polarized antenna loaded by polarization conversion metasurface is studied in this chapter.First of all,a polarization converter is designed based on reflective metasurface,which can realize the efficient performance of cross polarization conversion within frequency band of 4.1-8.6GHz.Then it is placed on the back of an omnidirectional linear-polarized microstrip antenna,and due to the polarization rotation effect,the whole antenna structure achieves the dual-band dual-circular-polarized radiation characteristics,meanwhile the gain increases about 4dB.This method may become a new approach for the CP antenna design and research.