A low profile polarization diversity planar antenna capable of effectively separating the horizontal and vertical polarization. The antenna combines a notch antenna (A) and a patch antenna (B) in a low profile structure. The notch antenna comprises a ground plate (10), a feed plate (20), and a radiator plate (30) which are stacked in a spaced relation. The radiator plate is shorted to the ground plate at its center and formed in its periphery with at least two radial notches (38). The feed plate carries feeder probes (27) each located adjacent to each one of the notches for feeding the notch antenna. The patch antenna comprises a patch (40) stacked above the radiator plate (30). The patch (40) is grounded at one portion thereof and has a feed point spaced from the grounded portion for feeding the patch antenna. The patch is grounded to the radiator plate and has a diameter smaller than the radiator plate. Thus, the notch antenna and the patch antenna have individual radiator elements with the radiator plate rendered as the ground plane for the patch antenna, the notch and patch antennas exhibit less mutual coupling so as to effectively separate horizontal polarization made by the notch antenna from vertical polarization by the patch antenna.