Axial ratio control of circularly polarized microstrip antenna using miniaturized multilayer graphene resistive pads

Abstract A circular to linear polarization conversion of microstrip patch antenna using miniature multilayer graphene (MLG) pads is proposed in this article. The antenna consists of a circular radiating patch fed with 90° Branch Line Coupler (BLC) making it circularly polarized. The tiny graphene nano pads are placed on either side of the BLC in a way that one end of graphene pad touches the BLC, and the other is shorted to ground. The resistance of the graphene pads varies from 250 Ω to 54 Ω by applying variable voltage (0 V−6 V). This voltage bias makes the graphene pads conductive and attenuates the power in one of the arms of BLC and thereby converting antenna from circular to linearly polarized mode. The antenna is designed to operate at center frequency 3.3 GHz having operational bandwidth of 420 MHz (3.13 GHz–3.55 GHz), axial ratio (AR) bandwidth of 288 MHz (3.255 GHz−3.543 GHz). By varying the bias, the axial ratio in this band can be tuned from < 3 dB to > 5 dB. The measured results are in good agreement with simulated and the proposed antenna can be used for C band wireless applications.