An antenna has a predetermined operating frequency, corresponding to a predetermined wavelength, and the antenna includes: a conductive sectoral horn including one open end built into a floorplan; short-circuited radiating slots, built into the floorplan, on either side of the open end; and conductive louvres, arranged above the slots and the open end, and configured to be deployed mechanically in a continuous manner to modify a radiation pattern of the antenna. The antenna can be, for example, used in stations for testing electromagnetic fields.