OAM vortex beams with spiral phase wavefronts have potential applications in optics and communi-cations. This letter proposes a reflective broadband hexagonal meta-atom structure based on the Pancharatnam-Berry (P-B) phase principle. The tight arrangement of this meta-atom allows the design of metasurfaces at 26-43 GHz to produce high-purity millimetre-wave vortex beams. A comparative simulation has been used to verify the better performance of hexagonal structures than square structures. According to the OAM spectral analysis, the mode purity of the hexagonal arrangement (0.89) is 10% higher than that of the square arrangement (0.81) at 40 GHz, demonstrating that the hexagonal meta-atom is essential in enhancing the mode purity of the OAM.