The invention relates to a wide-band omnidirectional antenna including at least a first conducting member and a second conducting member having a revolution symmetry about a common revolution axis and central openings, said members being arranged opposite each other, at least one member having a progressively flaring area, characterised in that it comprises a gap between the conducting members and a central coaxial excitation line so as to achieve a three-dimensional contactless transition between the coaxial excitation line and the conducting members and members for modifying the radiation pattern in the flaring area of the diode type for selectively radiating the gap depending on the on- or off-state of said diodes.