Accession Number : ADD013747
Title : Doppler-Improved Polyphase Pulse Expander-Compressor.
Descriptive Note : Patent, Filed 7 Apr 86, patented 29 Mar 88,
Corporate Author : DEPARTMENT OF THE NAVY WASHINGTON DC
Personal Author(s) : Kretschmer, Frank F , Jr
Report Date : 29 Mar 1988
Pagination or Media Count : 8
Abstract : This invention relates to pulse-type, peak-power limited radar systems, and particularly to methods and apparatus for frequency-derived pulse compression techniques used in peak-power limited radar systems. The present invention achieves a reduction in cyclic losses due to doppler shift in frequency-derived polyphase compression codes, such as the Frank, P1, P2, P3 and P4 codes, by altering the code. The modified code phases are derived by sampling the phase characteristics of an underlying chirp or step-chirp waveform at a rate which is higher than the Nyquist rate, thereby increasing the number of code elements within the uncompressed pulse length. These codes are no longer the same codes as before, but they are referred to as oversampled versions of the well known prior codes (e.g. oversampled Frank code). The cyclic losses decrease as the sampling rate increases. The oversampled codes may be expanded and compressed using a variation of the usual DFT (discrete fourier transform) or FET (fast fourier transform) phase filter procedures. Although amplitude weighting may be required to reduce the higher resulting sidelobe peaks, there is a significant increase in the resultant signal-to-noise ratio of the doppler shifted signal even with amplitude weighting.
Descriptors : *CODING, *DOPPLER EFFECT, *SIDELOBES, *SIGNAL TO NOISE RATIO, *PATENTS, AMPLITUDE, CYCLES, DISCRETE FOURIER TRANSFORMS, FAST FOURIER TRANSFORMS, FILTERS, LENGTH, LOSSES, PEAK POWER, PHASE, PULSES, RADAR EQUIPMENT, RATES, SAMPLING, WEIGHTING FUNCTIONS
Subject Categories : Active & Passive Radar Detection & Equipment
Radiofrequency Wave Propagation
Distribution Statement : APPROVED FOR PUBLIC RELEASE