On the basis of aperture coupled antenna, a wideband circularly polarized microstrip antenna coupled by orthogonal slots is designed in Ku band to broaden the bandwidth and improve the gain. In the antenna a layered structure with two square patches is taken as radiating elements, so the gain is improved with the broadening of the bandwidth. Coupling feedstructure is realized by adopting microstrip line with left-hand orthogonal slots (Left-Hand Orthogonal Slots) and the axial ratio is improved by optimizing slots size. The measured results show that 22.5% (VSWR<2) bandwidth and 16.2% 3 dB axial ratio bandwidth are achieved respectively and the gain is better than 9 dBi within 3 dB axial ratio bandwidth. The feed design of the antenna in the above structure is simple, and provides a reference for designing circularly polarized microstrip antenna.