Research On Plane Wave Polarization Control Technology

Polarization is an essential nature of plane electromagnetic(EM)waves,which carries the information about microscopic anisotropy,chiral feature,and spin orientation,it plays a central role when the EM waves interact with matter.Therefore,the polarization control technology is very promising in wireless communication and optical systems,and becomes a hot research topic in microwave,terahertz,and optical frequency bands.This thesis conducts in-depth research on polarization control such as polarization rotation,polarization conversion,and polarization selection.The main innovations of this dissertation can be summarized as follows:1.High-efficiency and wideband polarization rotator:We carefully analyze the possible operation modes inside the substrate integrated waveguide(SIW)cavity.Based on the distribution of the fundamental TM110 mode,a continuous polarization direction rotation from 0 to 45° can be achieved by using a SIW cavity with two twisted slots etched on center of front and back sides metal surfaces.Subsequently,two cascade SIW cavities with three twisted slots(twist angle is 45°)are employed to realize a conventional 900°polarization rotator.Experimental measurements and comparison of typical polarization rotators demonstrate that the proposed 90° polarization rotator features low insertion loss,high-efficiency cross polarization transmittance,and broad operating band.2.Linear polarizer immune to the polarization direction of an incident wave:Generally,traditional linear polarizers follow Malus's law,which indicates that the transmitted intensity is strongly dependent on the angle between polarizer's transmitted axis and the polarization direction of the incident wave.For a special angle of 90°,there would be no power transmitted through the linear polarizer at all.To overcome this shortcoming,we herein report a linear polarizer based on a two-dimensioned array of square substrate integrated waveguide cavities,which can convert an arbitrary linearly polarized incident wave into an outgoing LP wave in a specified polarization direction with constant transmittance.Experiment measurements demonstrate that the proposed linear polarizer has a stable transmittance of 50%and high polarization extinction ratio of over 45 dB,as well as immune to the polarization direction of an incident wave.Therefore,the proposed linear polarizer is extreme importance to promote the development of novel polarization selective structures.3.Two types of linear-to-circular polarization converters:In terms of conversion efficiency,structural thickness,and operating bandwidth,two different types of linear-to-circular polarization converters are reported here.(1)Slot-type frequency selective surface based linear-to-circular polarization converter,which can obtain the polarization conversion from linear to circular in a subwavelength or lower structural thickness.(2)Wideband linear-to-circular polarization converter based on dielectric gratings with periodic parallel strips.It features broad operating bandwidth of over 60%,low transmission loss and high polarization conversion efficiency,as well as stable performance under the oblique incidence.Microwave experiments are performed to successfully verify the individual polarization conversion characteristics for above two types of polarization converters.Finally,a detailed comparison between the proposed polarization converters and other typical designs is made,and also objectively discuss their own advantages and disadvantages,as well as their prospective applications.4.Planar-helix chiral metamaterials based circular polarizer:We first introduce the concept of the circular polarizer and its classification.Then,a high-efficiency and broadband circular polarization selective structure(CPSS)is proposed based on planar-helix chiral metamaterials,which can effectively reject the left-hand circularly polarized(LCP)incident wave,while allow the right-hand circularly polarized(RCP)wave to pass through it unimpeded.Physical mechanism of the proposed CPSS is clearly explained with the aid of the current distributions along the planar-helix under the excitations of LCP and RCP waves.The transmission characteristics of LCP and RCP waves for single-and dual-turn single-planar-helix are carefully analyzed,and finished the fabrication and measurement on the dual-turn planar-helix CPSS.Experimental results show that the proposed CPSS features a factional bandwidth of 75.6%for the transmittance of the LCP wave lower than 0.2,and high transmittance of over 0.9 for RCP wave,as well as high circular polarization selection efficiency of over 0.95.In addition,two feasible schemes to enhance the performance of the proposed CPSS are also discussed,and a detailed comparison between the planar-helix chiral metamaterials based CPSSs and other typical CPSSs is made to reveal their superior performance.Finally,based on the this CPSS designs,we also report another circular polarization converter,which can convert a RCP incident wave into an outgoing LCP wave.Experiments are also performed on the fabricated circular polarization converter,and the corresponding simulated and measured results are also provided.