中文摘要：

目前,广泛应用的环行器均需要铁氧体材料并外加偏置磁场以达到环行效果,具有重量大,对温度敏感等缺点.本文基于透射型相位梯度超表面,利用相位梯度超表面的异常折射特性,基于几何光学原理设计了一种无需铁氧体材料和外加磁偏置的环行器.实验结果说明,在20.8 GHz附近,该器件呈现显著的环行效果.这种环行器重量显著降低,对温度变化不敏感,提供了一种环行器设计的新思路,具有潜在的应用前景.

英文摘要：

Circulators are widely used microwave components that rely on magnetic materials. They have been a subject of extensively theoretical and experimental development for over 50 years. Nowadays, commercial circulators require ferrite and external bias magnetic field to realize circulation performance. However, ferrite circulators suffer major drawbacks：they are too heavy, incompatible with integrated circuit technologies, expensive, sensitive to temperature, etc. So, it is very hard to further improve the characteristic of traditional ferrite circulator. And it is important to overcome the major drawbacks of the traditional ferrite circulator. In this paper, the anomalous refraction feature of the phase gradient metasurface is utilized to realize nonreciprocal characteristics. Magnetless circulator based on phase gradient metasurface is proposed and then analyzed. The circulator consists of phase gradient metasurfaces and a three-port waveguide. Three metasurfaces are arranged into 60-degree angle with respect to each other. The metasurface shows high efficiency in anomalous refraction. With the help of phase gradient metamaterial, the signal can only be refracted to the next port in rotation along one direction. That makes the circulation performance. To design and optimize the circulator for better circulation performance, the numerical simulations are performed using the full-wave electromagnetic simulator CST Microwave Studio 2013. To verify the design of the circulator based on phase gradient metasurface, the circulator is fabricated using waveguide and metasurfaces. The scattering parameters of the magnetless circulator based on phase gradient metasurface are measured using a vector network analyzer（Agilent N5230A）. The measured S-parameters show that the circulator exhibits good circulation performances at a frequency of 20.8 GHz. At 20.8 GHz, the insertion loss is 0.8 d B. And the return loss and isolation degree can reach-10 d B. In this paper, a new method is used to design the circulators. This work