Abstract: In this paper,a new structure is proposed to improve the directivity of patch antenna.The substrate of the antenna incorporates photonic crystal,which has a triangular lattice.A defect is introduced at the central hole of the photonic crystal.Only the lower half of the central hole is removed,that is,the depth of the central hole is half of the depth of other holes.The patch is placed at the bottom of the central hole,which means the patch is inside the photonic crystal.The antenna using this new structure is numerically simulated with software HFSS.Numerical results demonstrate that radiation directivity is improved apparently.