1. In a synthetic aperture radar (SAR) system mounted on a moving platform, for producing radar pulses at a variable pulse rate interval (PRI) and carrier frequency, said SAR system effective for directing them toward a selected target region of predetermined relative location and dimensions, a pulse generator system comprising timer means for controlling the time at which said radar pulses are produced, frequency means for establishing a reference frequency value for comparison with radar return from said target region, modulator means responsive to said timer means for establishing the pulse width of said radar pulses and delivering said radar pulses to a transmitter power stage, said SAR system characterized in that it further includes control means for directing said timer means in modifying the time of production of said radar pulses by varying the PRI and for directing said frequency means controllably to vary said reference frequency to ensure that at least three independent points in said target region are maintained in focus.