Design And Application Of Polarization Conversion Metasurface

As a kind of two-dimensional structure designed artificially,electromagnetic metasurface has attracted much attention in recent years because of its unique electromagnetic characteristics.As one of them,polarization conversion metasurface provides a way to reconstruct the polarization of transmitted or reflected electromagnetic waves.Therefore,it has great potential to be applied in antenna design.At present,polarization conversion metasurface is mainly used in radar cross-section(RCS)reduction and circular polarization radiation.In this thesis,we focus on the application of polarization conversion metasurface in RCS reduction and circular polarization design.The main work includes the following aspects:(1)On the application of polarization conversion metasurface in antenna RCS reduction,an ultra-wideband polarization conversion metasurface unit is proposed,which achieves a polarization conversion ratio of more than 90% in the wide band of 6.79-27.56 GHz(relative bandwidth of 121%).Through the checkerboard arrangement,the broadband low RCS characteristic can be formed.In order to study its application in low RCS antenna,a low RCS slot array antenna is proposed by integrating polarization conversion metasurface and slot array antenna.The radiation characteristics and scattering characteristics of the low RCS slot antenna are simulated and measured.The results show that compared with the reference antenna,the low RCS slot antenna not only has no degradation in radiation characteristics,but also has good RCS reduction effect in wide band.(2)On the application of polarization conversion metasurface in wideband RCS reduction,a method to expand the RCS reduction bandwidth is proposed.Firstly,a polarization conversion metasurface with controllable working frequency band is designed by loading PIN diode.When the diode is in OFF state,the polarization conversion metasurface works in low frequency band;When the diode is in ON state,the polarization conversion metasurface works in high frequency band.Then the polarization conversion metasurface is arranged in a checkerboard style to form a reconfigurable metasurface.By adjusting the working state of PIN diode,the metasurface could have effective RCS reduction performance in two adjacent frequency bands,thus realizing the broadband scattering suppression characteristic.Finally,in order to verify the applicability of this method in antenna RCS reduction,a microstrip antenna is taken as an example to form a low scattering microstrip antenna by laying a certain number of reconfigurable polarization conversion metasurface elements around it.The simulation results show that the antenna also has adjustable scattering characteristics.Using the same method,the broadband RCS reduction effect is realized on the basis of guaranteeing the good radiation performance of the antenna.(3)On the application of polarization conversion metasurface in circularly polarized antenna,a dual-band dual circularly polarized microstrip antenna which can adjust the operating frequency band and direction of rotation is proposed.The antenna structure consists of a reconfigurable polarization conversion metasurface and an omnidirectional linearly polarized antenna.By changing the working state of the PIN diode,the working band and reflection phase of the polarization conversion metasurface can be adjusted,and then the working band and circular polarization rotation of the antenna can be switched.The results are as follows: when the PIN diode is switched to OFF state,the antenna works in the range of 8.82-9.17 GHz,which is left-hand circular polarization(LHCP);when the PIN diode is switched to ON state,the antenna works in the range of 10.35-10.89 GHz,which is righthand circular polarization(RHCP).