A dual-reflector microwave antenna comprises the combination of a paraboloidal main reflector having an axis; a waveguide and dual-mode feed horn extending along the axis of the main reflector, a subreflector for reflecting radiation from the feed horn onto the main reflector in the transmitting mode, and a shield extending from the outer edge of the main reflector and generally parallel to the axis of the main reflector, the inside surface of the shield being lined with absorptive material for absorbing undesired radiation. The subreflector is shaped to produce an aperture power distribution that is substantially confined to the region of the main reflector outside the shadow of the subreflector.The support for the subreflector is preferably a hollow dielectric cone having a resonant thickness to cause energy passing through said cone to be in phase with energy reflected off of said cone so as to achieve phase cancellation.