A GRATING LOBE SUPPRESSION TECHNIQUE FOR LINEAR FREQUENCY-STEPPED PULSE TRAINS
MITRE CORP BEDFORD MA
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Linear frequency-stepped pulse trains, periodic in both time and frequency, have ambiguity functions which are periodic in both delay and doppler. One way of suppressing these ambiguities or grating lobes is time and frequency staggering of sub-pulses in the train, smearing out the grating lobes into a delaydoppler residue level. However this works well only with a large number of sub-pulses and a small pulse train duty factor. Another approach, described here, is to chirp code each sub-pulse, filling in the pulse train signal in the frequency domain. This suppresses ambiguities in a strip parallel to the delay axis, giving an unambiguous time response with some doppler tolerance. The technique appears to produce acceptable time responses with either a small or large number of sub-pulses and with various pulse train duty factors. The doppler tolerance, however, depends strongly upon the duty factor.
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