Page "Synthetic aperture radar" Paragraph 24

Returns from scatterers within the range extent of any image are spread over a matching time interval.

The inter-pulse period must be long enough to allow farthest-range returns from any pulse to finish arriving before the nearest-range ones from the next pulse begin to appear, so that those do not overlap each other in time.

On the other hand, the interpulse rate must be fast enough to provide sufficient samples for the desired across-range ( or across-beam ) resolution.

When the radar is to be carried by a high-speed vehicle and is to image a large area at fine resolution, those conditions may clash, leading to what has been called SAR's ambiguity problem.

The same considerations apply to " conventional " radars also, but this problem occurs significantly only when resolution is so fine as to be available only through SAR processes.

Since the basis of the problem is the information-carrying capacity of the single signal-input channel provided by one antenna, the only solution is to use additional channels fed by additional antennas.

The system then becomes a hybrid of a SAR and a phased array, sometimes being called a Vernier Array.