A Yagi-Uda monopolar antenna configured to be mounted on the conductive surface of a vehicle, especially an aircraft. The antenna comprises: a radiating element, taking the form of a conductive plate, for example one having the shape of a disc, which plate is equipped with a return conductor; a reflecting element; and at least one directing element taking the form of a monopole that is folded on itself. The various elements are mounted on a substantially planar surface such as the skin of the fuselage of an aircraft. The antenna simultaneously has a wide operating band, a good compactness and a good directivity. It may especially serve as joint antenna for a plurality of air-ground communication systems of an aircraft.