The elimination of standing waves in aerials employing paraboloidal reflectors

The standing waves produced in a matched wave guide when it is placed at the focus of a paraboloid are analysed along the lines of classical diffraction theory. From the theory it is possible to deduce the size of a flat plate which, when fixed to the apex of the paraboloid, eliminates this source of reflection. The experimental results obtained with a paraboloid of aperture 20¿ are in good agreement with the theory. The radiation pattern of the paraboloid is slightly affected by the plate, and the type of deterioration observed is consistent with an approximate theory of the effect. In the course of the investigation, a combination of flange and diaphragm was developed which matches the wave guide to free space over a wide band of wavelengths, and which can be used for radiating peak powers up to 750 kW.