Abstract: A system for determining the magnitude and direction of the relative velocity of two objects wherein a first of the objects, for example an aircraft, transmits a continuous sequence of radar pulses from a broad beam antenna directed toward the second object, e.g., the ground, and a receiver, also mounted on the aircraft, receives the echo returns of the pulses through an antenna which has a pair of phase center locations spaced apart along the axis of the aircraft. The two receiving phase centers are electrically displaceable in directions lateral to the aircraft axis (heading) and are controlled to follow substantially the same ground track. The positions of the phase centers are also "dithered" laterally to enable automatic tracking of aircraft drift angle.