Abstract: A radar processor is disclosed for processing the radar return samples from a Doppler radar receiver to discriminate helicopter targets from fixed-wing targets. The radar processor defines the spectral components of the radar return components due to the helicopter rotor hub as the “signal” component; and the spectral components due to the target skin, ground clutter and white noise as the “noise” component. The radar processor implements the Neyman Pearson criterion to calculate a detection statistic. Whether the calculated detection statistic exceeds a threshold determines whether a “helicopter presents” or a “helicopter absent” target condition is declared. The radar processor utilizes helicopter rotor hub reflected signals, and requires only a few milliseconds on target, and may therefore be readily implemented by scanning surveillance systems.

Abstract: A method is provided for reducing quadratic phase errors in synthetic aperture radar signals from a plurality of range lines where each range line includes a plurality of azimuth positions. The method includes receiving a plurality of slow-time samples representing radar signals for a plurality of azimuth positions for a plurality of range lines. A plurality of corrected samples and an initial quadratic phase error coefficient are identified based upon the slow-time samples. The corrected samples are processed according to a superresolution signal processing technique to thereby obtain a plurality of estimated Doppler frequencies for a plurality of point scatterers at each range line, after which a true signal for each range line is reconstructed based upon the plurality of estimated Doppler frequencies. A correction to the initial quadratic phase error coefficient is then obtained based upon the corrected samples, the true signals and the initial quadratic phase error coefficient.

Abstract: SAR images are improved by a method for acquiring a synthetic aperture image from a sequence of periodic pulse returns where the sequence of periodic pulse returns is interspersed with interrupts, i.e. missing pulses. The interrupts mark the start and end of one or more segments, where the segments contain the periodic pulse returns form the SAR image. The method comprises the steps of: converting said pulse returns into a digital stream; performing an azimuth deskew on said digital stream to obtain a deskewed digital stream; forming a forward-backward data matrix from the deskewed digital stream for one or more segments; forming an average segment covariance from the forward-backward data matrix; computing a model order for the average segment covariance; computing one or more linear prediction coefficients using data contained in the forward backward data matrix, and model order; using the linear prediction coefficients to compute missing pulse returns belonging within the interrupts.

Abstract: A system is provided for reducing errors in synthetic aperture radar signals from a plurality of range lines where each range line includes a plurality of azimuth positions. The system comprises an autofocus processor for receiving a plurality of slow-time samples. The autofocus processor can estimate a phase error for each slow-time sample by a maximum likelihood technique and thereafter compensate the plurality of slow-time samples by the estimated phase errors to obtain a plurality of range-line samples. The implementation of the maximum likelihood technique is done by a superresolution technique along slow-time samples which also estimates a plurality of Doppler frequencies and amplitudes for a plurality of point scatterers at each range line. Further, the autofocus processor can also predict the performance of the autofocus technique by computing a resulting root mean square error of the estimated phase error which is derived form the corresponding Cramer Rao bound.

Abstract: A signal processing system and method capable of real-time implementation for extracting signal parameter information with high accuracy and resolution. Signals (101) are passed through a filter bank (102), downconverted and decimated. The superresolution technique of constrained total least squares (CTLS) is used to process the resulting samples to obtain frequency components and their amplitudes (106). CTLS may also be used to obtain decaying coefficients associated with each frequency components. If desired, the results of CTLS may be used to extend original data for higher resolution spectral analysis and output (109).

Abstract: A radar processor is disclosed for processing the radar return samples from a Doppler radar receiver to discriminate helicopter targets from fixed-wing targets. The samples are passed through a helicopter filter which eliminates the target skin Doppler return, and passed the sidebands about the target skin return which are due to the helicopter rotor hub modulation. The coefficients of the helicopter filter are selected to maximize the signal-to-noise ratio. The radar processor requires only a few milliseconds on target for reliable detection and can, therefore, be easily implemented by scanning surveillance systems.