Palindromic polyphase code expander-compressor

Communications: radio wave antennas – Antennas – Balanced doublet - centerfed

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343 5FT, G01S 1328

Patent

active

045660115

ABSTRACT:
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..sub.n =.+-..pi.(n-1/2).sup.2 /.rho. for a PP-3 code or .phi..sub.n =.+-[pi.(n-1/2).sup.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..

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Linear Frequency Modulation Derived Polyphase Pulse-compression Codes and Efficient Digital Implementation, B. L. Lewis and F. F. Kretschmer, Jr., NRL Report 8541, Nov. 2, 1982.
A New Class of Polyphase Pulse Compression Codes and Techniques, B. L. Lewis and F. F. Kretschmer, Jr., IEEE Transactions on Aerospace and Electronic Systems, vol. AES-17, No. 3, May 1981.

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