Analysis and design of terahertz reflectarrays based on graphene cell clusters

In this paper, the graphene cell-cluster is introduced, which is composed of an array of identical unit-cells placed in a geometrical configuration. Such graphene cell-clusters are then used for the realization of a reflectarray. To the best of our knowledge, identical unit-cells in a particular geometrical configuration have already been introduced, but the analytical formulas for this model have not been investigated so far. In this paper, the Fourier-optics and aperture field estimation methods are applied to investigate the effect of cell-cluster dimensions on the generation of specified far-field radiation patterns. Implementing cell-clusters in graphene reflectarrays and similar structures, and also applying the proposed formulas, lead to the simplicity of configuration and enhancing the design accuracy. First, the effect of cell-cluster dimensions on the reflectarray radiation pattern is investigated. Then, a reflectarray composed of graphene cell-clusters is designed. A new configuration of graphene unit-cell composed of two graphene layers is proposed, where a middle layer of metallic patch is inserted. In the common graphene unit-cells, the rate of amplitude variations is quite high and greatly depends on the variation of phase in the proposed unit-cell. However, the amplitude variation is quite smaller than the phase variations.