Imaging synthetic aperture radar
First Claim
1. A pulsed synthetic aperture radar having real-time motion compensation, comprising:
- (a) means to transmit a signal to a field of view;
(b) means to receive a returned signal scattered from said field of view;
(c) means to process said returned signal to obtain coarse-resolution in azimuth, then to obtain fine-resolution in range, and then to obtain fine-resolution in azimuth, all as functions of actual radar motion to create a real-time radar image of said field of view.
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Accused Products
Abstract
A linear-FM SAR imaging radar method and apparatus to produce a real-time image by first arranging the returned signals into a plurality of subaperture arrays, the columns of each subaperture array having samples of dechirped baseband pulses, and further including a processing of each subaperture array to obtain coarse-resolution in azimuth, then fine-resolution in range, and lastly, to combine the processed subapertures to obtain the final fine-resolution in azimuth. Greater efficiency is achieved because both the transmitted signal and a local oscillator signal mixed with the returned signal can be varied on a pulse-to-pulse basis as a function of radar motion. Moreover, a novel circuit can adjust the sampling location and the A/D sample rate of the combined dechirped baseband signal which greatly reduces processing time and hardware. The processing steps include implementing a window function, stabilizing either a central reference point and/or all other points of a subaperture with respect to doppler frequency and/or range as a function of radar motion, sorting and compressing the signals using a standard fourier transforms. The stabilization of each processing part is accomplished with vector multiplication using waveforms generated as a function of radar motion wherein these waveforms may be synthesized in integrated circuits. Stabilization of range migration as a function of doppler frequency by simple vector multiplication is a particularly useful feature of the invention; as is stabilization of azimuth migration by correcting for spatially varying phase errors prior to the application of an autofocus process.
106 Citations
23 Claims
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1. A pulsed synthetic aperture radar having real-time motion compensation, comprising:
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(a) means to transmit a signal to a field of view; (b) means to receive a returned signal scattered from said field of view; (c) means to process said returned signal to obtain coarse-resolution in azimuth, then to obtain fine-resolution in range, and then to obtain fine-resolution in azimuth, all as functions of actual radar motion to create a real-time radar image of said field of view. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21)
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22. A pulsed synthetic aperture radar having real-time motion compensation, comprising:
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(a) means to transmit a signal to a field of view and means to adjust at least one of the following parameters of said transmitted signal on a pulse-to-pulse basis in response to actual radar motion;
center frequency, starting phase, and chirp rate;(b) means to receive a returned signal scattered from said field of view and means to mix said returned signal with a local oscillator waveform and an A/D converter having A/D sampling locations and sampling frequencies which are controlled as a function of radar motion, said A/D converter to convert said mixed signal to a digital dechirped baseband signal, said local oscillator waveform also having parameters of center frequency, staring phase, and chirp rate that can be varied on a pulse-to-pulse basis in response to radar motion; (c) means to process said returned signal to create a real-time radar image of said field of view.
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23. A pulsed synthetic aperture radar, comprising:
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(a) means to transmit a signal to a field of view; (b) means to adjust at least one of the following parameters of said transmitted signal on a pulse-to-pulse basis in response to actual radar motion;
center frequency, starting phase, and chirp rate;(c) means to receive a returned signal scattered from said field of view; (d) means to process said returned signal using overlapping subapertures to obtain, first, coarse-resolution in azimuth, then to obtain fine resolution in range, and then to obtain fine-resolution in azimuth, all as function of actual radar motion to create a real-time radar image of said field of view.
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Specification