A new aperture plane method of measuring antenna surface errors

A scheme for measuring surface errors of reflector antennas is proposed in which the phase of the signals from small areas of the wavefront are compared one by one to the phase of the signal from the rest of the wavefront. The comparison is accomplished by periodically changing the phase of the signal from each small area by ±90°. For convenience and economy, the measurement can be made in an aperture plane of an antenna feed system, and can be done in real time with the antenna pointing steadily at the source being observed. Estimates are made of the signal power required for the measurement, and three means of modulating the phase are suggested, one of which allows the surface error of the antenna to be corrected as well as measured