A 640 MHz 32 megachannel real-time polyphase-FFT spectrum analyzer

A 2²⁵ (33,554,432) channel, 640 MHz wide polyphase-fast Fourier transform (FFT) spectrum analyzer is being designed at the Jet Propulsion Laboratory for the Search for Extraterrestrial Intelligence (SETI) Sky Survey. By replacing the time-domain multiplicative window preprocessing with polyphase filter processing, much of the processing loss of windowed FFTs can be eliminated. Polyphase coefficient memory costs are minimized by effective use of run-length compression. Finite word length effects are analyzed, producing a balanced system with 8 bit inputs, 16 bit fixed-point polyphase arithmetic and 24 bit fixed-point FFT arithmetic. Fixed-point renormalization midway through the computation is seen to be naturally accommodated by the matrix FFT algorithm proposed