Lockheed Martin Corporation

Loral Corporation

Bruce H Ferrell

William C Woody

John A Garnaat

A notched-chirp generator (20), utilizing first and second chirp generators (28, 30), a functional conversion element (40), an antichirp generator (42), a summing element (64), and a translation element (66), generates a notched-chirp signal (24). The second chirp generator (30) generates a second chirp phase signal (.phi..sub.C1), is translated by the functional conversion element (40) into an oscillating antichirp signal (A.sub.O1). The antichirp generator (42) generates an antichirp signal (A.sub.1) by scaling, weighting, and cyclically positioning the oscillating antichirp signal (A.sub.O1). The summing element (64) sums the antichirp signal (A.sub.1) with a first chirp phase signal (.phi..sub.C0), generated by the first chirp generator (28), to produce a notched-chirp phase signal (.phi..sub.N), which is converted by the translation element (66) into a notched-chirp signal (24) having a notch (26) positioned at a specific frequency (f.sub.N) determined by the antichirp signal (A.sub.1)

Notched-spectrum swept-frequency generator and method therefor

The data is processed using a quadratic phase removal process to remove quadratic phase variations contained in the interference to compress the interference to its narrowest extent in a range frequency dimension. Partial motion compensation may be optionally employed using the partial motion compensation process to remove incidental Doppler modulation of the interference caused by motion of the radar during data collection, and to center the Doppler spectrum of radar and interference signals at a convenient frequency. The data is processed using an azimuth Fourier transform to compress the interference to its narrowest extent in an azimuth dimension to localize the interference into peaks while leaving the desired radar signals dispersed throughout the data in one or both dimensions. Optionally, another set of interference data, collected and interleaved with the radar video data and delayed a short time with respect to it, may be compressed in range frequency using a similar quadratic phase removal process and partially motion compensated to remove effects of undesired aircraft motion using a partial motion compensation process and compressed in azimuth using an azimuth FFT. The 2-D compressed interference data is then subtracted from the 2-D compressed radar video data by a subtraction process. The data is processed using a thresholding process to find interference peaks in the data. The found peaks are attenuated by attenuating azimuth cells and range cells. The data is processed using a second azimuth Fourier transform to restore the data to its original format. The data is then processed to produce an image for display. This is achieved by processing the data using a final motion compensation process to provide reference point tracking to remove the phase change imparted by the intentional motion of the aircraft during data collection, polar resampling the motion compensated data, weighting and two-dimensional Fourier transforming the polar resampled data, and autofocusing 25 the data to produce the image for display.

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Litchfield Park, AZ, United States of America

Bruce H Ferrell