A single-layer reflecting element is proposed based on the principle of linear-to-circular polarization conversion focusing metasurface, which can independently control the phases of x-polarized and y-polarized reflecting waves and operate in a broadband of 10–14 GHz. Following the generalized Snell's laws of reflection, a super cell is designed with a phase-gradient of ?60° for x-polarized waves and 60° for y-polarized waves, and the simulation results show the well wideband anomalous reflection as expected. In the design of the multifunctional metasurface, the 13 × 13 unit cells are used to satisfy the parabolic profile and the focal-distance-to-diameter ratio is set to be 0.5. The phase compensation for forming a constant aperture phase is provided by the individual reflected elements with different structure parameters and?x??y =90° is used to realize polarization conversion. The designed sample is simulated in CST Microwave Studio and the results show that both of the x-polarized and y-polarized plane waves are well focused through the reflection of the focusing metasurface in a broadband of 10–14 GHz. Traditionally, multi-layer element is used to broaden phase coverage and bandwidth, the single-layer design in this paper greatly reduces the cost, processing difficulty and thickness of the lens. For further application, a linearly polarized Vivaldi antenna with a highest gain of 10 dB is located at the focal point of metasurface and the angle included between its polarization direction and x-axis is 45° in order to acquire right-handed circularly polarized reflecting wave. According to the reversibility principle of electromagnetic wave propagation, the spherical wave radiated by the feed antenna is converted into plane wave by the reflection of the focusing metasurface so that the antenna gain is remarkably enhanced. Simultaneously, the linearly polarized wave can be transformed into circularly polarized wave. Finally, the feed antenna and the metasurface are fabricated, assembled and measured. Numerical and experimental results are in good agreement with each other, which shows that the?1 dB gain bandwidth of the high-gain antenna is 24%(11–14 GHz) and the 3 dB axial ratio bandwidth is 29.8%(10–13.5 GHz). In addition, the gain at 12 GHz reaches a highest value of 19.6 dBic, and the aperture efficiency is more than 54%. The good performances indicate that the proposed broadband high-gain circularly polarized antenna has a well promising application in various communication systems. It is worth noting that the horizontally polarized, vertically polarized, right-handed circularly polarized and left-handed circularly polarized high-gain antenna can be realized with the rotation of feed antenna. In this case the idea is more versatile and valuable for designing the polarization reconfigurable antenna systems.%基于线-圆极化转换原理和聚焦超表面相关理论,设计了一种反射型宽带线-圆极化转换聚焦超表面,并结合线极化馈源设计了宽带的高增益圆极化天线.首先,提出了一种单层的变形十字超表面单元,单元具有极化独立特性,并且能够在10—14 GHz宽频带范围实现对反射波相位360°范围全调控,同时利用该单元构建的一维超单元很好地验证了奇异反射现象.然后,分别控制单元横向和纵向尺寸的分布构建出同时满足线-圆极化转换和聚焦条件的双功能超表面.最后,采用Vivaldi天线作为馈源对超表面进行照射组成天线系统,仿真及测试结果均表明天线系统同时实现了高增益和线-圆极化转换,系统的?1 dB带宽为24%,?3 dB轴比带宽为29.8%.本文的设计充分体现了超表面对电磁波相位和极化操控的灵活性,具有显著的应用前景.
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