Terahertz (THz) antennas can be used for high-speed indoor wireless communications. The antennas must have a wide bandwidth, high gain, and low loss. In this study, a dielectric resonator antenna fed by the photonic crystal (PC) waveguide based on a newly developed silicon-on-glass technology is proposed and analyzed. The PC waveguide is designed by float-zone silicon that can help propagation guided modes with low loss. Coupling matching between waveguide and antenna, and also between the antenna and free space can be analyzed by coupling mode theory. The reflection loss at the interface between the components is minimized using three matching air holes. The proposed compact antenna operates at 325 GHz with about 5.2% bandwidth. The end-fire antenna is introduced with a high gain of about 12 dBi, low loss, and sidelobe levels of −11 and −8.8  dB in the E- and H-planes. The high efficiency of over 97% in the entire antenna operational bandwidth is achieved. The platform is used for THz communications at the high data rate.