In this article, a coupled line diplexer (operating at 2.4 GHz and 3.5 GHz) which can be used as single-band filter with tunable attenuation characteristics in the pass band has been designed. Multilayer graphene (MLG) pads are used to achieve tunable features in this circuit. The graphene pads are placed at each branch of the diplexer. Single-band tunable attenuation characteristics are achieved by applying bias to graphene pads placed at optimum locations on the filter. The proposed tunable coupled line attenuating diplexer is realized on FR-4 glass epoxy substrate of thickness 1.58 mm with a total size of 45 × 75 mm2. By varying the bias voltage (0 V –6 V) of MLG pads the resistance of graphene pad placed in the circuit gets decreases thereby attenuating/controlling the transmission power to the other port in the required band. In lower pass band (2.28–2.55 GHz) the signal is attenuated from 3 to 10.8 dB and in higher pass band (3.2–3.58 GHz) signal is attenuated from 5 to 13 dB. Simulations of the structure with and without graphene pads have been carried out and are in good agreement with measured results.
