In this paper, a W-band single-layer reflectarray antenna is proposed with the advantages of broadband and high aperture efficiency. A novel dual rotation-symmetry windmill element is designed in the W-band, which consists two layers of copper patches printed on a Rogers RT5880 substrate. Based on the analysis of the proposed metasurface element, a square reflectarray with $13.85\lambda _{0}$ (44.2 mm) aperture diameter at 94 GHz center frequency was designed, fabricated and measured. The designed reflectarray antenna shows a 1-dB gain bandwidth of 25.5% (89-113 GHz) in the W-band. Moreover, the measured gain is 31.1 dBi at 94 GHz and the maximum aperture efficiency is 53.4%. The result shows that the proposed design has prospects in wireless communication applications.
