Graphene is being used as a patch as it possesses a number of desirable electromagnetic and mechanical properties that assist in providing flexible and reconfigurable antenna structure. A graphene reflective unit cell is examined to demonstrate that the reflection coefficient can be controlled by changing the chemical potential and size of the graphene patch. The phase compensation of the reflected waves is achieved by patches with different sizes. Reflection coefficient phase variations for 0°–525° with a variable slope are obtained for different graphene conductivities. A graphene-based reflectarray antenna is proposed. A reflect array with dimensions of that operates at 1.6 THz is analyzed. The reflectarray is composed of 40x40 unit cells with for each unit cell size. They are placed upon silicon dioxide substrate. A horn antenna is used as a feed. The focal-length-to-diameter (F/D) ratio is equal to one. A maximum gain of 20.7, 13.6, and 21.4 dBi are obtained at 1.4, 1.8, and 1.6 THz respectively.