The Reserch Of Polarization Converter Based On Frequency Selective Surface

This thesis presents the work of the author involved in the project of"the research of the polarization rotator based on frenquency selective surface".The traditional frequency selective surface(FSS)is a two-dimensional periodic array structure which is essentially a kind of spatial filter,which can filter some specific frequencies and reflect others.The FSS has been wildly applied in reducing the cross section area of radar,and realizing multiplexing and beam separation as the Cassegrain antenna subreflector or the quasi optical system filter.In this thesis,based on the function of the traditonal frequency selective surface,the polarization converter based on frequency selective surface was proposed.The linear to circular polarization converter which can convert the incident linear polarization wave to circular polarization wave,and the linear polarization rotater which can rotate the linear polarization direction of the incident wave to other linear polarization directions.In addition,we designed and simulated the linear polarization rotater based on chiral structure which was achieved by the characteristics of chiral material,and it can rotate the linear polarization directions of twoelectromagnetic waves which perpendicular to each other other45°along the clockwise directionsimultaneously.1.The operation frequency of the linear to circular polarization converter we designed was 22GHz.The testing results showed that the energy transmission parameter of the linear to circular polarization converter was-0.18dB in the center frequency 22GHz,and the axial ratio(AR)was 1.OldB,and the AR bandwidth below 3dB was 24.82%,and the transmission bandwidth above-1dB is 4.27%.2.This thesis discussed the feasibility of rotating the linear polarization direction of electromagnetic wave to any other degrees.We designed and manufactured30°,45° and 90° linear polarization rotaters to verify the feasibility.The operation frequency of the three linear polarization rotaters were all 22GHz.The testing results showed that the transmission parameter of 30°,45°and90° linear polarization rotater was-0.19dB,-0.46dB,-0.24dB respectively and the transmission parameter above-1dB was 4.77%,5.45%,4.45%respectively.3.Thisthesis discussed the fundamental theory to realize linear polarization rotating using chiral materials.The operation frequency of the designed linear polarization rotater based on chiral structure was 22GHz.The testing results showed that the polarization rotation of the two electromagnetic waves which had the perpendicular polarization have been achieved,and the transmission parameter was-0.16dB,and the transmission bandwidth above-1dB is 2%.All of the polarization converters were fabricated based on the periodic slots structure of copper.Comparing with the traditional structures which were applied in polarization rotation,such as waveguide polarization rotater,wire-grid polarizer,Faraday rotation modulators and so on,the periodic slots structure is simpler,easier to fabricate.As the polarization converters designed without other medium materials besides copper,it can be uses in high-power field.