In this paper, a graphene-based reflectarray antenna using ENZ (Epsilon-Near-Zero) metamaterial at terahertz (THz) band is proposed, and the performance of its unitcell is investigated. Then, the phase distribution and radiation pattern of the antenna are examined. Benefiting from exceptional complex surface conductivity of graphene which is a novel 2-d material, the size reduction of reflectarray has been facilitated as a result of plasmonic mode propagation within the structure which in turn leads to an increase in propagation constant. Moreover, tunneling phenomenon in ENZ material, a kind of metamaterial which has a relative permittivity under 1, helps reduce the loss. Taking advantage of these outstanding features of both materials, the proposed reflectarray is designed to function at 2.5 THz and is composed of 150×150 elements with square-shape configuration. We have achieved 40 dB of gain using the combination of graphene and ENZ material in reflectarrays, and also it is the first that time they are used together in the reflectarray. This work mainly focuses on the impact of using ENZ material and graphene simultaneously which is not done before, then the results demonstrate that it has a considerable effect on increasing the reflectarray gain.
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