Detection of Radar Weak Signals Using cross Spectral Density

摘要

A technique of correlation and cumulation is proposed for the detection of weak signals buried in the noise, e.g. spread-spectrum radar signals at low signal to noise ratio (SNR), on the foundation of analysis of the different statistical character between spread-spectrum signals and noise. Using a pair of antennas, spatially separated by a distance of the order of one meter or more, with broadband receivers, cross correlating the outputs of two receivers, produces a cross correlation function (CCF), in which the noise components are spread uniformly over the whole width, while the signal component, the narrow autocorrelation function (ACF) of the spread-spectrum signal, is concentrated in the center. A simple time-domain filter can select this narrow center portion of the CCF, rejecting the remainder which contains only noise. Taking the Fourier transform of this windowed CCF produces the 'time-domain filtered cross spectral density' (TDFCSD). Cumulating TDFCSD in a certain period eliminates the remainder noise more, the weak signals then can be detected and characterized. A computer simulation illustrates the signal processing process involved, and the results shows excellent agreement with the analysis.