Feed arrangement for axis definition of paraboloid reflector

An arrangement is proposed for the determination of the electrical axis of a paraboloid, utilising the effects of the subsidiary axial maxima that occur when the paraboloid is illuminated by a plane wave. By combining the signal received at the largest of these maxima with a sample taken from the main received signal in antiphase, a null detection system gives the location of the axis with high sensitivity. This is sufficient to enable the combination to be used to detect small distortions of the paraboloid, and as a precise axis-location device.