An antenna is provided which is structured to operate at two frequency bands simultaneously. The antenna is structured as a waveguide cavity having two types of radiating elements provided on its top surface, symmetrically about the diagonal of the cavity. One group of radiating elements is optimized to operate at one frequency band, while the other group is optimized to operate at a first frequency band. In one implementation, two groups of holes of different diameter are provided on the top surface of the cavity and the radiating elements are two groups of cones of different diameter coupled to different diameter holes. The different diameter holes act as a filet between the two frequency bands.