Abstract: A dished reflector is illuminated by a primary radiation feed including a rectangular waveguide and a secondary radiation feed comprising two dipoles flanking that waveguide. In order to minimize distortion of the radiation diagram from the secondary feed by the waveguide envelope, at least one elongate corrective member paralleling the dipoles is externally mounted on that envelope and is capacitively coupled or conductively connected thereto at a location where a peripheral current induced by the dipoles is at a maximum. The corrective member, like the dipoles themselves, may be a plate with major faces lying in planes perpendicular to the waveguide axis.