We propose to integrate a high-gain open-ended rampart slot array antenna in our edge-coupled terahertz (THz) photonic
transmitters. By locating the open circuits at the end of each quarter-wavelength slot antenna, the reflected terahertz
wave can constructively interference with the input wave and hence produce higher gain. In addition, the folded feeding
networks turn more propagating waves into the effective radiating segments rather than the dispersive surface waves. A
THz resonant cavity is also designed under our monolithic THz-wave circuits. A 300-nm gold layer is coated below the
substrate to serve as a reflecting mirror to reflect back the THz waves to the antenna. The resonant cavity design not only
provides a robust base for post device process but also greatly enhances the gain of antenna. With the design of openended
rampart slot array antenna and THz resonant cavity, we demonstrate that the gain of antenna can reach 8~9 dBi.