A small antenna including a dielectric plate, upper and lower conductive plates provided on upper and lower faces of the dielectric plate, respectively, a plurality of conductive reactance posts for connecting, at first positions of the dielectric plate, the upper and lower conductive plates to each other, and a feed point provided at a second position of the dielectric plate such that first and second plane-parallel plate transmission lines separated from each other by the reactance posts are formed by the upper and lower conductive plates.