In this paper, we have simulated 2D photonic crystal (dielectric slab with regular cylindrical periodic lattice of air-gap) as substrate to enhance the electrical performance of the microstrip (rectangular or circular) patch antenna at THz/millimeter wave frequencies. The periodic structures designed to open up frequency bands within which the propagation of electromagnetic waves is forbidden irrespective of the propagation direction. We also simulated the role of depth of the 2D air gap in the photonic crystal used as substrate materials.