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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 mo

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. Reflected pulses received at the forward and aft phase center locations are non-coherently detected and a computing system performs a time-amplitude comparison of the pulse amplitude values detected at the aft phase center location against the pulse amplitude values detected at the forward phase center location N pulse repetition intervals earlier in time. The relative velocity between the aircraft and the ground is calculated as a function of the pulse repetition frequency.

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