Abstract: A dual-polarization planar antenna includes: a first feeding substrate having a plurality of first radiation elements and a first feeding line; a first dielectric member; a first ground conductor having a plurality of slots; a second dielectric member; a second feeding substrate having a plurality of second radiation elements and a second feeding line; a third dielectric member; and a second ground conductor. The first feeding substrate, the first dielectric member, the first ground conductor, the second dielectric member, the second feeding substrate, the third dielectric member, and the second ground conductor are successively superposed in this order. The first feeding substrate, the first ground conductor, and the second feeding substrate are arranged so that the slots, the first radiation elements, and the second radiation elements are overlapped with one another at the same positions.