Optical EngineeringAnalysis of ladar range resolution enhancement by sinusoidal phase modulation
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The ability of a ladar system to resolve two or more separate returns from a combined echo is related to the effective correlation bandwidth of the pulse emitted by the ladar system. Phase modulation of an outgoing pulse introduces additional frequency components, which increases the effective correlation bandwidth of the pulse and thus improves the range resolution of the system. In this paper, we discuss the general theoretical basis for achieving improved range resolution using a modulated waveform and a matched filter receiver. We then demonstrate these concepts by considering the particular case of improved range resolution for a sinusoidally phase modulated carrier with a rectangular amplitude function. We also perform computer simulations with a realistic pulsed ladar envelope possessing the same modulation function. Our calculations indicate that the resolution of a pulsed ladar system may be improved by a factor of 70 with a phase-modulated pulse and a matched-filter receiver.