An orthomode junction for separating and/or combining orthogonally-polarized radiofrequency wave signals, comprises a body which has a main cavity forming a main waveguide, which has a blind end, and auxiliary cavities forming auxiliary waveguides, which communicate laterally with the main cavity in the vicinity of the blind end thereof, and a deflection insert situated at the blind end of the main cavity and facing the auxiliary cavities, the deflection insert having different shapes on the side of the auxiliary cavities respectively.