Wideband Fine Frequency Measurement (FFM) by Pipelined Digital FFT Apparatus

Recently available commercial digital chip technology makes it possible to offer NRL a digital fine frequency measurement (FFM) spectral analyzer design based on the fast Fourier transform (FFT) that meets or exceeds the measurement specifications posed by this SBIR topic. A VME card-based configuration is proposed that performs a 500-MHz bandwidth analysis with a 90-dB dynamic range, a 2-microsecond analysis time (throughput latency), a frequency resolution 1/1 024 of the analysis bandwidth (488 KHz), and a pipelined arrangement that permits a new FFT to be started every 0.5 microseconds (sustained 10 mega-pulses-per-second throughput). This 500-MHz analyzer is estimated to fit on four 6U VME cards using a combination of two unique VME card designs in its un-pipelined configuration (.5 Mpps throughput) or twenty VME cards in its pipeline configuration (10 Mpps throughput). The design concept can be arranged in a second configuration that performs a 1-GHz bandwidth analysis, which is estimated to fit on eight 6U VME cards using a different combination of the two VME card designs. A digital design offers several advantages over analog power spectral analyzer designs, such as acoustooptical approaches, including stability, no need for calibration, and additional analysis output such as the phase spectrum (which is not produced by analog designs).