This work presents a sub-THz transmitter scheme for wireless communications with beam steering capabilities based on photonics means. A true time delay 1x4 beamforming photonic chip is designed in Si3N4 technology to continuously tune the progressive time delay between consecutive antenna elements. Simulation results show a progressive delay up to 15 ps with a bandwidth of 1.3 GHz, enabling broadband operation at frequencies above 75 GHz. The sub-THz signals are generated on photoconductive antennas on chip by photonic heterodyning. The design of a dielectric rod antenna array is also presented to efficiently radiate the generated wave.