A quad-beam reflectarray fed by a single feed horn is designed in W-band at 105 GHz. The feed horn is designed with the goal of being manufactured in a single metallic piece by a CNC milling process. The reflectarray is circular with a periodicity of 0.857 mm and comprised of 15 380 rectangular patches in a single layer of metallization. The four beams are realized by means of the superposition principle and positioned in a great circle corresponding to (𝜃, 𝜑) = (30°, 0°). The reflectarray is simulated in HFSS modelling each element as a copper patch with a gold coating to avoid corrosion. Simulations show that more than 30 dBi of gain per beam and a gain variation of 1.1 dB are achieved in the frequency range 103 GHz–109 GHz, making suitable for future 6G ultra-capacity fixed wireless access enabled by travelling wave tubes.