Attenuation‐tunable balanced bandpass filter based on graphene nanoplates

Abstract

In this letter, a unique type of balanced bandpass filter (BPF) with high selectivity and tunable attenuation is proposed through the comprehensive design of a microstrip balanced BPF and graphene nanoplates. In order to achieve the passband response in differential-mode (DM) excitation and produce a wide and deep stopband in common-mode (CM) excitation, the balanced couple of lines are used in balanced BPF. The graphene nanoplates are loaded on the open ends of λ/4 stepped-impedance resonators to dissipate the electromagnetic field. By raising the bias voltage applied to the graphene nanoplates, the values of the graphene's surface impedance can be adjusted from high to low. The insertion loss of the balanced BPF can be indirectly tuned while maintaining the return loss at a comparatively low level. A prototype of the proposed gain tunable balanced BPF is fabricated and measured. The measured results show that a tuning range of insertion loss from 1.75 to 10.7 dB can be obtained for the DM circuit over the operating bandwidth centered at 1.84 GHz, without interrupting the signal rejection of the CM circuit.