Magnetless circulator based on phase gradient metasurface

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 N5230 A). 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 dB. And the return loss and isolation degree can reach -10 dB. In this paper, a new method is used to design the circulators. This work makes it possible to reduce the weight of the device. Moreover, it is also insensitive to temperature. Therefore, we can make a conclusion that the magnetless circulator based on phase gradient metasurface has potential value in application. However, there is still lots of work to do to improve the performance of the circulator. In future work, we will use wideband metasurfaces to broaden the bandwidth, improve the isolation degree, reduce the insertion loss, and reduce the return loss. And free space can be lead into the circulator to reduce the bulk of the circulator and improve the circulation performance.