We present three linearly polarized photoconductive terahertz (THz) antenna designs for a THz imaging system that we are constructing. A bow-tie based antenna with a finite ground plane (on the side of the substrate opposite the bow-tie) and DC bias lines included, is the reference design. By making the ground plane larger, one is able to increase the directivity of the bow-tie design at 1.05 THz. On the other hand, by incorporating a metamaterial-inspired structure, which acts as an artificial magnetic conductor (AMC), the directivity is increased by almost 3 dB at 1.05 THz. The simulation results show that the radiation efficiency of this bow-tie AMC-augmented antenna is above 85% at 1.05 THz. A comparison of these three antenna designs is given.