A novel terahertz detector is here proposed, based on the use of planar arrays of graphene nanoribbons of different widths and lengths. Two distinct mechanisms are exploited to detect an external incident field: the excitation of interband transitions and of the surface plasmon polaritons resonances. The tuning of such mechanisms allows strengthening the signal, so providing an alternative solution to the problem of the low efficiency of the resonant graphene antennas. This paper proposes a possible design solution and analyzes and the feasibility of tuning the two mechanisms in the THz range.