基于方形开口环的超宽带线性极化转换器

Ultra-wideband linear polarization converter based on square split ring

电磁波的极化调控在卫星通信、雷达探测以及立体显示成像等领域有重要的应用价值,探索易于加工、转换效率高、工作频带宽的高性能极化转换器具有重要的研究意义.本文提出了一种基于方形开口环超构表面的线性极化转换器,该转换器具有各向异性特点,反射电场沿两个对角线方向的分量振幅相等,相位相差180°,导致在反射模式下能够将入射波的极化方向旋转90°.实验测试结果表明,在7.12—18.82 GHz频带范围内极化转换率高于90%,相对带宽达到90%.频带的显著拓宽基于四个谐振频点,每个谐振频点的转换效率都接近100%.实验结果与模拟结果相符合,验证了提出的超构表面可以在较宽的频带范围内实现电磁波的90°极化旋转.

Polarization state of electromagnetic wave has important applications in satellite communication,radar detection,and stereoscopic display imaging.Therefore,the control of polarization state of electromagnetic wave is an important direction in scientific research.The traditional method of manipulating the polarization state is mainly realized based on Faraday effect and birefringent crystal,which has a certain requirement for the material thickness(leading to large volume),and does not have broadband characteristics(leading to narrow band).Recently,metamaterial with subwavelength meta-atoms,has achieved many exotic phenomena and functionalities that cannot be found in nature.As an important branch of metamaterial-based devices,polarization converter has attracted great attention and achieved significant progress.However,most of them cannot realize ultra-broadband,high-efficiency,wide-angle,and simple geometry simultaneously.In this paper,a linear polarization converter based on a square split ring metasurface is proposed.Due to the anisotropic structure,the amplitudes of the reflected electric field along the two diagonal lines are equal,and their phase difference is 180°.As a result,the polarization direction of the incident wave can be rotated 90°.The simulation results show that the polarization conversion ratio(PCR)is higher than 90%in a frequency range from 7.12 to 18.82 GHz,which means that the relative bandwidth reaches 90%.The significant bandwidth expansion is attributed to the four electromagnetic resonances generated in a square-split-ring unit.We investigate the influence of geometric parameters on PCR in detail.We also examine the performance of the proposed structure under oblique incidence.It has little effect on the co-polarization and cross-polarization reflection coefficients when the incident angle is changed from 0°to 45°.Even if the incident angle reaches 45°,the mean PCR remains above 80%.The PCRs of the four electromagnetic resonant points are all close to 100%.Finally,we fabricate and measure the proposed polarization converter that contains 30×30 unit cells.The experimental results are in good agreement with the simulation results,and thus validating the design.In conclusion,we propose both theoretically and experimentally a linear polarization converter that possesses ultra-broadband,high-efficiency,wide-angle,and simple geometry simultaneously.The proposed scheme can be extended to terahertz and even optical frequencies.