基于交叉极化旋转相位梯度超表面的宽带异常反射

Broadband anomalous reflector based on cross-polarized version phase gradient metasurface

设计实现了一种基于双圆弧形金属结构的宽带反射型极化旋转超表面,在7.9—20.1 GHz的宽频带范围内交叉极化转换率达到99%,通过改变其结构参数可实现在保持高效的交叉极化转换率的条件下对交叉极化反射相位的自由调控.基于六种不同结构参数极化旋转超表面结构单元的空间排布设计实现了一维宽带相位梯度超表面,在宽频带内,实现了异常反射.测试了其镜面交叉极化反射率,与仿真结果基本一致.仿真计算了x-极化波入射时的电磁场分布和异常反射角度,与理论计算结果基本一致.仿真与测试结果均表明这种相位梯度超表面在8.9—10 GHz和10.0—18.1 GHz的两个宽带频率范围内可分别实现高效的表面波耦合和异常反射.

Phase gradient meatsurface（PGM） is a new way to control reflective beam and refractive beam.By means of PGM,wave-fronts can be controlled in a more freedom way.The generalized Snell＇s law was put forward first by Nanfang Yu et al.[Yu N F,Genevet P,Kats M A,Aieta F,Tetienne J P,Capasso F,Gaburro Z 2011 Science 333 334]to describe the anomalous refraction on PGM.Anomalous refraction and out-of-plane reflection were then demonstrated using PGM composed of V-shaped nanoantennas.As deeper research about PGM,many reflective PGMs are also proposed.Typical examples are the reflective PGM using H-shaped resonators by Lei Zhou＇s group and using split-ring resonators by Shaobo Qu＇s group,both acting as high-efficiency surface wave couplers.However phase gradient of most PGMs above are achieved in a narrow-band and cannot change the polarizations.Anomalous reflection can only be realized in a certain narrow-band,and anomalous reflective angles cannot be precisely predicted.In this paper,a polarized conversion metasurface based on double-circular metallic resonator is first designed.The conversion successfully achieves ultra-wideband cross-polarization for linearly-polarized waves within a broadband of 12.2 GHz（from 7.9-20.1 GHz）with more than 99%cross-polarized reflectance.On the premise of high efficiency,reflective phase can be regulated by changing geometrical parameter of double-circular metallic structure.Then a broadband one-dimensional dispersive phase gradient metasurface comprised of six unit cells periodically arrayed above substrate is designed and fabricated.The PGM can perfectly achieve anomalous reflection.Measured result about its specular reflectivity is in good agreement with simulated result.Moreover,the measurement results of El-field distribution and anomalous reflective angle nearly accord with simulation results.Anomalous reflective angle is precisely predicted based on the generalized Snell＇s law.Both simulation and experiment verify that the PGM can make incident waves efficiently coupled as surface waves from8.9-10 GHz and anomalously reflected in a range from 10 GHz to 18.1 GHz.