Exploitation of graphene as HIS and RIS for devices in the MW and THz frequency ranges

Graphene has become an outstanding material for revolutionary wireless applications in the microwave and terahertz/infrared frequency ranges. Due to its unique physical characteristics, a family of completely new devices can be developed by exploiting graphene's behaviour as High Impedance Surface (HIS) or highly-Reactive Impedance Surface (RIS). In this paper we theoretically investigate first a 10 GHz-resonant gold dipole antenna suspended over a graphene flake acting as a HIS reflector: the radiator can be placed at a very close distance from the graphene ground by keeping at the same time very good radiation performance with respect to classical metal reflectors. Second, we consider a gold dipole antenna operating at 10 THz directly attached to a graphene layer. Excellent radiation performance can be achieved thanks to the highly-inductive surface impedance of graphene at such high frequencies. An in-depth description of the possibility of varying graphene's conductivity by means of an applied gate voltage is provided, thus demonstrating how radiating properties can be tuned by simply applying a proper voltage to the reflector. Hence, the proposed antennas can be considered in reason as the starting point for innovative graphene-based mm- and μm-systems with unique tunability properties.