For wireless networks beyond 5G, directivity and reconfigurability of antennas are highly relevant. Therefore, we propose a linear antenna array based on photodiodes operating at 300 GHz, and an optical phased array based on polymer waveguides to orchestrate the antennas. Due to its low thermal conductivity and high thermo-optical coefficient, the polymer chip enables highly efficient and crosstalk-free phase shifting. With these, we demonstrate purely photonic-controlled beam steering across 20°. Compared to a single emitter, the 3-dB beam width is reduced by 8.5° to 22.5° and the output power is >10 dB higher. Employing Snell's law for coupling into air, we can precisely predict the radiation patterns.