A Tunable Attenuator Based on a Graphene-Loaded Coupled Microstrip Line

In this article, a novel tunable attenuator based on graphene is proposed. It consists of a coupled microstrip line (CMSL) and two graphene-covered gaps in MSLs. By utilizing a biased voltage, the surface impedance of graphene can be tuned, and then, the reflective coefficient at two ports of the coupler can be correspondingly adjusted; therefore, the performance of the attenuator can be modified. The design procedure and the mechanism of the attenuator are demonstrated in detail. To verify the analysis, a prototype was fabricated and tested. According to the measured results, the fabricated attenuator presents the favorable attenuation tuning range from 3 to 20 dB at the operating frequency from 1 to 6 GHz, and it is just 38 mm × 22 mm in size. Besides, |S11| of the attenuator can always be maintained at a low level, and the phase of S21is substantially unchanged.