In this paper, a frequency reconfigurable THz antenna is presented. The antenna is a microstrip antenna including a rectangular patch and a slotted ground plane. To realize frequency reconfigurable antenna in THz band, graphene is used instead of PIN diodes. The antenna is enable to work in different modes by changing the parameters of graphene. This ability can replace ON or OFF state of the diode. By working in these different modes, the operation frequency of the proposed antenna changes from 2.8 to 4.2 THz. Suitable radiation patterns, wide impedance bandwidth more than 10%, a good impedance matching, and an average gain of 2dB are achieved throughout the most the antenna’s operation states.
