An antenna is provided. The antenna includes a radiator, a feed conductor and a ground conductor. The radiator includes a body and a parasitic element. An aperture is formed on the body, and the body encloses the aperture. The parasitic element is connected to the body and extended into the aperture, wherein the parasitic element is connected to the body at a parasitic location. The feed conductor is connected to the body, wherein a signal, fed to the body by the feed conductor, travels on the body, and passes the parasitic location to the parasitic element. The ground conductor is connected to the body.