Abstract: A device for controlling radiofrequency beams comprising a set of cells. Each cell comprises a support frame and an excitation element, and emits and/or receives beams in an invariant manner according to the direction of propagation of the beam. The frame is inscribed within a generally tubular shape, oriented along the axis Z of a reference frame, having a cross section of perimeter P, and comprises an entrance, an exit and a number N of slots between the exit and a position Zo located between the entrance and the exit. Each slot has a variable width along Z. The slot width has a minimum value at the position Zo, and a maximum value at the exit that is determined on the basis of the perimeter P and the number N.