An antenna comprising: a dielectric substrate; and an antenna element including, a power feeding element including a first conductive layer formed over the dielectric substrate, the first conductive layer extending in a first direction from a first position on an end of the first conductive layer and having a first length along the first direction; and a reference potential element including, a second conductive layer formed over the dielectric substrate, the second conductive layer extending away from the first position in a second direction opposed to the first direction from a second position and having a second length along the second direction, the second position being apart by a first distance along the second direction from the first position, and a third conductive layer formed over the dielectric substrate, the third conductive layer extending from the second conductive layer in the first direction, being apart by a second distance along a third direction perpendicular to the first direction from the first conductive layer, and having a third length along the first direction; wherein the first distance and the second distance are the same as each other and correspond to a desired input impedance, characterized in that: the antenna further comprises: a second one of the antenna element for forming a pair of antenna elements which are arranged parallel to each other on the dielectric substrate and a short circuiting conductive layer to couple together the reference potential elements of the antenna elements, the short circuiting conductive layer being formed over the dielectric substrate and having a fourth length; and a first set of switches to change positions at which the short circuiting conductive layer is coupled to each of the reference potential elements. a dielectric substrate; and an antenna element including, a power feeding element including a first conductive layer formed over the dielectric substrate, the first conductive layer extending in a first direction from a first position on an end of the first conductive layer and having a first length along the first direction; and a reference potential element including, a second conductive layer formed over the dielectric substrate, the second conductive layer extending away from the first position in a second direction opposed to the first direction from a second position and having a second length along the second direction, the second position being apart by a first distance along the second direction from the first position, and a third conductive layer formed over the dielectric substrate, the third conductive layer extending from the second conductive layer in the first direction, being apart by a second distance along a third direction perpendicular to the first direction from the first conductive layer, and having a third length along the first direction; wherein the first distance and the second distance are the same as each other and correspond to a desired input impedance, characterized in that: the antenna further comprises: a second one of the antenna element for forming a pair of antenna elements which are arranged parallel to each other on the dielectric substrate and a short circuiting conductive layer to couple together the reference potential elements of the antenna elements, the short circuiting conductive layer being formed over the dielectric substrate and having a fourth length; and a first set of switches to change positions at which the short circuiting conductive layer is coupled to each of the reference potential elements. the antenna further comprises: a second one of the antenna element for forming a pair of antenna elements which are arranged parallel to each other on the dielectric substrate and a short circuiting conductive layer to couple together the reference potential elements of the antenna elements, the short circuiting conductive layer being formed over the dielectric substrate and having a fourth length; and a first set of switches to change positions at which the short circuiting conductive layer is coupled to each of the reference potential elements. a second one of the antenna element for forming a pair of antenna elements which are arranged parallel to each other on the dielectric substrate and a short circuiting conductive layer to couple together the reference potential elements of the antenna elements, the short circuiting conductive layer being formed over the dielectric substrate and having a fourth length; and a first set of switches to change positions at which the short circuiting conductive layer is coupled to each of the reference potential elements.