Adaptive line enhancement and spectrum analysis

The notion that adaptive filters may estimate and track the frequency of a phase-modulated sinusoid in noise better than a spectrum analyzer is examined. It is argued, using both theoretical and experimental results, that spectrum analysis performs better than adaptive filtering. In addition, the method of spectrum analysis can be improved for such applications by the use of frequency-slope processing, or by the generation of a partially coherent reference waveform by maximum posterior probability estimation of the phase function.