Manipulating the propagating direction and polarization state of electromagnetic wave is always fascinating and used in a wide field. One of the approaches to achieving this aim is typically based on steering the propagation phase of wave traveling inside an optical medium, such as dielectric lens. Nevertheless, this approach creates new problems, such as high loss, bulky volume and fabrication difficulty. Recently, metasurface was found to be a two-dimensional equivalence of metamaterial, which attracted a great deal of attention because of its unique properties and capability of manipulating and controlling electromagnetic waves on a sub-wavelength scale. So metasurface serves as an alternative approach to dealing with the loss and fabrication issues, and opens a door for bridging the gap between the fundamental research of the artificial structures and their device applications. n A reflective phase gradient metasurface (PGM) achieving the linear-to-circular (LTC) polarization conversion and anomalous reflection simultaneously is designed in this paper. Firstly, the conventional cross-shaped structure is modified for enlarging the phase range. Then, six modified cross-shaped structures are designed cautiously to serve as quarter wave-plates, and achieve 60◦ phase difference between adjacent structures. The reflection phase difference between x-and y-direction components is 90◦, and their magnitudes are both equal to 0.5. Secondly, a one-dimensional PGM is constructed by distributing six modified cross-shaped quarter wave-plates one by one. Furthermore, an LTC polarization converter with an area of 216 mm × 216 mm is designed by placing 36 × 6 one-dimensional PGMs periodically. The mirror reflectivity and axial ratio are simulated and measured to verify the performances of LTC polarization conversion and anomalous reflection. The measured sample is fabricated by printing circuit board technique through using FR4 substrate, and a free space method is adopted in measurement in the anechoic chamber. In addition, the operating bandwidth can be evaluated from the reflective power density spectra. The measured results of mirror reflectivity, reflective power density spectra and axial ratio characteristic are in good agreement with the corresponding simulations, which shows that the mirror reflectivity is lower than −10 dB; the axial ration is lower than 2 dB within the frequency band of 13.8—14.7 GHz. Meanwhile, the theoretical reflection angles from the generalized Snell law are consistent with the CST microwave studio simulated results and measured results. Compared with the reported LTC polarization converters, the proposed LTC polarization converter not only achieves polarization conversion, but also can manipulate the output wave direction, thereby it has an important promising application value for microwave engineering and communication system.%本文设计了同时具有线-圆极化转换和出射波偏折功能的反射型极化转换器.通过六个不同结构参数的改进型十字结构四分之一波片组成一维相位梯度超表面,将此超表面分别在x和y 方向进行周期排布,设计了极化转换器.通过理论分析、仿真计算和实验测试,验证了该极化转换器在13.8—14.7 GHz频带内实现了高效线-圆极化转换和奇异反射.仿真并测试了镜面反射率、反射功率密度谱和轴比特性,仿真结果和测试结果的一致性良好,结果表明该极化转换器在13.8—14.7 GHz频带内的镜面反射率小于−10 dB,轴比小于2 dB,而且反射波的偏折方向与理论分析相一致.
展开▼
