Synthetic aperture radar for nonlinear trajectories using range relative doppler processing and invariant mapping
First Claim
1. A radiant energy detection system wherein electromagnetic energy is transmitted toward an object, the system having detection means for detecting presence of a received target signal, signal processing means for processing received signals, a computer for providing command, timing, and synchronizing control signals for the detection system operation, a synthetic signal synthesizer coupled between said detection means and said computer for receiving command and timing control signals from said computer and for providing in-phase and quadrature (I and Q) output signals to said detection means, said detection means providing I and Q outputs to said signal processing means;
- and wherein said synthetic signal synthesizer comprises an impulse generator having an input coupled to receive said timing signals from said computer and having an output;
first and second modulators each having respective first and second inputs, said first inputs being coupled to said computer for receiving I and Q sequences from the computer and said second inputs being coupled to receive said output of said impulse generator, said timing signals being indicative of real time occurrence of return signals from target scatterers and prompting the impulse generator to provide the output pulses to the second inputs of said modulators, said modulators modulating the received output pulses with the respective I or Q sequence received from the computer to provide a modulated output that is precisely coordinated with the return signal from the scatterers present in the I and Q sequence signals;
each modulator having an output pulse train; and
first and second low pass filters having respective inputs coupled to respective first and second modulator outputs for receiving respective outputs therefrom;
said first and second filters having an impulse response which matches the impulse response of the system and providing I and Q outputs respectively.
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Abstract
Synthetic aperture radar imaging for nonlinear trajectories utilizing range relative doppler processing, invariant mapping of information from arbitrary shaped cells onto an X--Y coordinate system, and round trip signal delay which allows accurate synthesis of a reference signal for each range cell. A synthetic signal synthesizer produces the reference signal for synchronous demodulation in the radar.
38 Citations
12 Claims
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1. A radiant energy detection system wherein electromagnetic energy is transmitted toward an object, the system having detection means for detecting presence of a received target signal, signal processing means for processing received signals, a computer for providing command, timing, and synchronizing control signals for the detection system operation, a synthetic signal synthesizer coupled between said detection means and said computer for receiving command and timing control signals from said computer and for providing in-phase and quadrature (I and Q) output signals to said detection means, said detection means providing I and Q outputs to said signal processing means;
- and wherein said synthetic signal synthesizer comprises an impulse generator having an input coupled to receive said timing signals from said computer and having an output;
first and second modulators each having respective first and second inputs, said first inputs being coupled to said computer for receiving I and Q sequences from the computer and said second inputs being coupled to receive said output of said impulse generator, said timing signals being indicative of real time occurrence of return signals from target scatterers and prompting the impulse generator to provide the output pulses to the second inputs of said modulators, said modulators modulating the received output pulses with the respective I or Q sequence received from the computer to provide a modulated output that is precisely coordinated with the return signal from the scatterers present in the I and Q sequence signals;
each modulator having an output pulse train; and
first and second low pass filters having respective inputs coupled to respective first and second modulator outputs for receiving respective outputs therefrom;
said first and second filters having an impulse response which matches the impulse response of the system and providing I and Q outputs respectively. - View Dependent Claims (2, 3, 4, 5, 6)
- and wherein said synthetic signal synthesizer comprises an impulse generator having an input coupled to receive said timing signals from said computer and having an output;
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7. A radiant energy detection system wherein electromagnetic energy is transmitted toward and reflected energy is received from an object, the system having synchronous detection means for detecting presence of a received target signal;
- signal processing means for processing received signals, a computer for providing command, timing, and synchronizing control of the detection system operation;
a synthetic signal synthesizer coupled between said synchronous detection means and said computer for receiving command and timing control signals from said computer and for providing in-phase and quadrature (I and Q) output signals to said detection means, said detection means providing I and Q outputs to said signal processing means;
invariant mapping processing means coupled between said signal processing means and said computer for mapping inputs from the signal processing means onto an absolute x--y reflectivity map prior to coupling out the information to said computer;
display means coupled to said computer for displaying information received by the system; and
a coherent oscillator for providing a synchronization signal output; and
wherein said synthetic signal synthesizer comprises first and second modulators having respective first inputs coupled to said computer and each having a second input and an output, an impulse generator having an input coupled to said computer and having an output coupled to the second inputs of said modulators, and an array of mixers and adders coupled to provide said I and Q output signals from said synthetic signal synthesizer to said synchronous detection means, said mixers having first inputs selectively coupled to said modulator outputs and having respective second inputs coupled to receive an input from said coherent oscillator for providing respective in-phase and quadrature output signals from each modulator output signal, said mixers having outputs selectively coupled to said adders, said adders having inputs coupled to said mixer outputs and providing the I and Q output signals as modulated quadrature IF signals to the synchronous detection means. - View Dependent Claims (8, 9)
- signal processing means for processing received signals, a computer for providing command, timing, and synchronizing control of the detection system operation;
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10. In an aperture radar system wherein electromagnetic energy in the form of a modulated carrier signal is transmitted toward an object and reflected energy is received from the object, the system having a synchronous detection circuit for synchronous detection of a target signal, digital signal processing means for processing received signals and computer means for providing command and tinning control signal outputs and synchronizing control of the radar system operation, the improvement comprising:
- synthetic signal synthesizing means coupled between said synchronous detection circuit and said computer means for receiving said command and timing control signals from said computer means and for providing in-phase and quadrature (I and Q) output signals to said synchronous detection circuit to provide enhanced cross-range resolution in linear geometries and optimum resolution in nonlinear geometries; and
invariant mapping processing means coupled between said signal processing means and said computer for mapping inputs from the signal processing means onto an absolute x--y reflectivity map prior to coupling out the information to said computer;
a coherent oscillator for providing a synchronization signal output; and
wherein said synthetic signal synthesizing means comprises an impulse generator having an input coupled to receive said timing signals from said computer and having an output;
first and second modulators having respective first inputs coupled to said computer and each having an output; and
an array of mixers and adders coupled to provide said I and Q output signals from said signal synthesizing means to said synchronous detection circuit;
said mixers having first inputs selectively coupled to said modulator outputs and having respective second inputs coupled to receive an input from said coherent oscillator for providing respective in-phase and quadrature output signals from each modulator output signal, said mixers having outputs selectively coupled to said adders, said adders having inputs coupled to said mixer outputs for providing the synthetic signal synthesizer I and Q output signals as modulated quadratic IF signals to the synchronous detection circuit; and
said modulators each having respective second inputs coupled to receive the output of said impulse generator, said timing signals prompting the impulse generator to provide output pulses indicative of real time occurrence of target scatterer return signals to said second inputs of said modulators, and said modulators modulating the received output pulses with the respective I and Q sequences received from the computer, thereby providing a modulated output that is precisely synchronized to occur with the return signal from scatterers present in the I and Q sequences. - View Dependent Claims (11, 12)
- synthetic signal synthesizing means coupled between said synchronous detection circuit and said computer means for receiving said command and timing control signals from said computer means and for providing in-phase and quadrature (I and Q) output signals to said synchronous detection circuit to provide enhanced cross-range resolution in linear geometries and optimum resolution in nonlinear geometries; and
Specification