Beam-steering of THz MIMO antenna using graphene-based intelligent reflective surface

In this work, beam-steering in THz MIMO antennas has been demonstrated using two different types of graphene-based intelligent reflective surface. Equivalent circuit models of intelligent reflective surface unit cells have been proposed for demonstrating their reflection characteristics. Two types of microstrip patch-based THz MIMO in side-by-side configuration and orthogonal configuration have been designed to exhibit S-11 lower than - 15 dB and radiation efficiency greater than 95%. Band-stop FSS has been employed to reduce the mutual coupling of MIMO antennas which are arranged in side-by-side configuration. The MIMO antennas have been integrated with graphene-based intelligent reflective surface for simultaneous steering of four beams radiated by the antenna elements. The reflectivity of the intelligent reflective surface relies on the conductivity of graphene which can be modified by changing its bias voltage. A digital 1-bit coded metasurface has been designed using graphene-based intelligent reflective surface. By varying the bias voltage on the graphene-based unit cells, the pattern of the digital code is modified on the intelligent reflective surface, which causes beam-steering of MIMO antennas placed above it. Gain improvement of 4 dB takes place when the intelligent reflective surface behaves as an AMC for the MIMO in linear configuration. Maximum gain improvement of 10 dB is obtained for the intelligent reflective surface integrated MIMO in orthogonal configuration with radiation efficiency greater than 90%. Numerical simulations using finite integration technique have been performed for illustrating the rotation of beam in MIMO antennas.