An Approximate Fast Fourier Transform Technique for Vernier Spectral Analysis
NAVAL UNDERWATER SYSTEMS CENTER NEW LONDON CT
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An approximate and quick fast Fourier transform technique for vernier spectral analysis is derived and tested for several candidate time-and delay- weightings, and for overlaps of the time weightings. For 50 percent overlap, the use of a simple cosine lobe for the time weighting yields spurious spectral sidelobes at least 23 dB below the main peak, whereas Dolph-Chebyshev time weighting achieves -33 dB sidelobes. For 75 percent overlap, use of a cosine sup 5 lobe for the time weighting yields sibelobes at least 54 dB down, whereas Dolph-Chebyshev time weighting achieves -86 dB sidelobes. In both cases of overlap, use of delay weighting is also required and is taken as a Hanning weighting. Extensions to other overlaps and weightings are possible from the fundamental relations presented and from the sample program furnished.
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