Palindromic polyphase code expander-compressor

摘要

A digital pulse expander-compressor for generating polyphase coded pulses which are highly doppler tolerant and have autocorrelation functions which are identical under frequency sweep reversal. The expander-compressor comprises an input expansion circuit for generating N replicas of a pulse to be expanded, a matched filter FFT with phase weights disposed in each input thereto, and phase inverters disposed in every other output therefrom, and a time dispersion circuit for appropriately adding the pulses from the FFT output to yield an expanded or compressed pulse. The phase weights to be inserted at the inputs to the FFT are determined by the equation phi n=+/- pi (n-1/2)2/ rho for a PP-3 code or phi n=+/-[ pi (n-1/2)2/ rho - pi (n-1/2)] for a PP-4 code, where rho is the pulse compression ratio and n varies from 1, 2, 3 . . . rho .