Abstract: A wideband high-gain substrate integrated cavity (SIC) circularly polarized antenna array is presented for Ku-band application. By introducing a pair of crescent-shaped patches placed at an angle along the SIC aperture and the feed slot at the bottom of the SIC, the high-order modes TM211 and TM121 in the SIC are adjusted to have the same amplitude and a phase difference of 90°, and realize high-gain circularly polarized radiation. Meanwhile, the dual parasitic patches also introduce a cavity-backed slot-coupled dipole circularly polarized radiation, which broadens the antenna circularly polarized radiation bandwidth. On this basis, a 2×2 sequential-rotation SIC antenna array is designed with a compact double-layer SIW sequential-phase feeding network. The measured results show that the proposed antenna array has an overlaid bandwidth of 21.30% from 10.74 GHz to 13.30 GHz while considering the -10 dB reflection coefficient, 3 dB axial ratio, and 3 dB gain bandwidth properties, and a measured gain of up to 14.50 dBi.