Clutter cancellation achievable with a digital waveform generator subjected to clock timing jitter

Abstract

As digital-to-analog converters get ever faster and more accurate, it becomes ever more feasible to replace analog waveform generation for a transmit exciter with digital circuitry. Simple equations have been obtained which relate clutter cancellation achievable with an LFM pulse compressor to clock timing jitter variance, LFM waveform bandwidth, digital IF frequency, and the sampling frequency. Equations derived in this paper show that the clutter cancellation ratio consists only of terms which contain the standard deviation of the jitter squared, /spl sigma//sub /spl tau///sup 2/ and terms with jitter raised to the 4th power, /spl sigma//sub /spl tau///sup 4/. All /spl sigma//sub /spl tau///sup 2/ terms are inversely proportional to the number of samples in the LFM waveform. The /spl sigma//sub /spl tau///sup 2/ terms dominate when the combination of jitter, digital IF, and waveform bandwidths are low enough. All jitter /spl sigma//sub /spl tau///sup 4/ terms are not reduced by the number of samples and do not benefit by an increase in sampling frequency. The /spl sigma//sub /spl tau///sup 4/ terms dominate when the combination of jitter, digital IF,and waveform bandwidths are too large. Clutter cancellation performance as it depends upon timing jitter is evaluated numerically for a variety of parameter values and checked by simulation. The results show that good clutter cancellation performance can be achieved with a digital waveform generator provided that the timing jitter is low enough for the digital IF and waveform bandwidth used.