Low side lobe gregorian antenna

A microwave antenna comprising the combination of a paraboloidal main reflector (10); a subreflector (13) located such that the paraboloidal main reflector (10) and the subreflector (13) have a common focal point (F) lying between the main reflector (10) and the subreflector (13); a feed horn (11,12) for transmitting microwave radiation (preferably symmetrically) to, and receiving microwave radiation from, said subreflector (13); and a shield (30) connected to the peripheral portion of the subreflector (13) and having an absorbing surface (31) which reduces side lobe levels both by capturing the feed horn spillover energy and by reducing the diffraction of microwave radiation from the edge of the subreflector (13). The shield (30) is preferably formed as a continuous axial projection extending from the periphery of the subreflector (13) toward the main reflector (10) substantially parallel to the axis of the feed horn (11,12). The reflective surface of the subreflector (13) is suitably a section of an approximate ellipse.