Abstract: The disclosed antenna includes: a radiating element disposed in a radiating plane transverse to an axis of the antenna; a reflecting plane, which is transverse to the axis, the radiating plane being located at a predetermined height above the reflecting plane; and a substrate, interposed between the radiating plane and the reflecting plane, and having a constant thickness. This antenna is characterized by a local relative electrical permittivity of the substrate that is a function of the radius, i.e. the distance to the axis, and a height, i.e. a distance to the reflecting plane, the local relative electrical permittivity being, at constant height, increasing as a function of the radius, and, at constant radius, increasing as a function of the height at least for a portion of the substrate in the vicinity of the reflecting plane.