Properties of phase synchronizing sources for a radio camera

A distorted phased array can be made to operate as a diffraction-limited aperture if a compensating time delay and/or phase shift is added in each antenna element channel. When the distortion is not known a priori the correction mast be based upon phasefront measurements of the radiation from a source external to the array. The ideal adaptive synchronizing source is a point source radiating in free space. The phasefrouts of realistic sources are perturbed, however. Three types of practical sources and calculations of the conditions under which their radiation fields are acceptable for adaptive beamforming are discussed. The sources are the passive reflector, the active beacon, and radar ground clutter.