An antenna device is provided. The antenna device includes an antenna body portion configured to transmit and/or receive a radio frequency (RF) signal, and including a dielectric material having a first dielectric constant; a metal layer configured to contact the antenna body portion; a first insulation layer configured to cover at least a part of the metal layer; and an electrical connection structure configured to be electrically connected to the metal layer, wherein the first dielectric constant of the antenna body portion is larger than a dielectric constant of the first insulation layer, and is smaller than a dielectric constant of the metal layer.