In this work, we present the design of a terahertz (THz) pyramidal horn antenna. The antenna is designed to operate in the frequency range of 220 GHz to 330 GHz, and is optimized for low side lobe levels and high gain. The design process involves the use of CST Microwave Studio software to model the antenna’s electromagnetic behavior and optimize its performance. A standard WR $3.4 (0.864 \times 0.432$ mm$^{2}$) waveguide is used to feed the antenna. The final design achieves a gain of 30 dBi in simulation and is fabricated using state-of-the-art manufacturing techniques. The designed THz pyramidal horn antenna exhibits excellent performance in terms of gain, bandwidth, and side-lobe levels, making it a promising candidate for use in THz communication systems.