Frequency tunable graphene metamaterial reflectarray for terahertz applications

A graphene-based metamaterial (GMM) reflectarray antenna with frequency tunable radiation characteristics has been investigated in this study. The unit-cell element consists of graphene split-ring-resonator (SRR) with two gaps printed on a grounded SiO2 substrate. The electrical properties of the metamaterial unit-cell have been determined at different graphene chemical potentials and different SRR gaps using the waveguide simulator. The metamaterial unit-cell element introduces negative epsilon(r) and mu(r) over a wide frequency band starting from 390 to 550 GHz. A reflectarray unit-cell element based on the GMM is designed at different frequencies. The phase compensation of the reflected waves is achieved by changing the SRR gap width. Reflection coefficient phase variations for 0 degrees-301 degrees with a variable slope are obtained for different graphene conductivities. Three different 13 x 13 GMM reflectarrays are designed and analysed at different graphene chemical potentials. A maximum gain of 22.6, 19, and 21.5 dB with side lobe level (SLL) is 11.31/9.15, 10.98/5.31, and 7.31/8.45 dB in an E/H-plane for the reflectarray arrangements (I), (II) and (III), respectively. An averaging phase curve is calculated to construct a single structure GMM reflectarray with frequency tunable radiation characteristics. A maximum gain of 21.8 +/- 1 dB with improved SLL of 13 dB was achieved.