Synthetic Aperture Radar (SAR) Imaging System

• US 20100039313A1
• Filed: 11/27/2007
• Published: 02/18/2010
• Est. Priority Date: 11/27/2007
• Status: Active Grant

• Current Assignee: Northrop Grumman Systems Corporation (Northrop Grumman Corporation)
• Original Assignee: Northrop Grumman Systems Corporation (Northrop Grumman Corporation)
• Inventors: Morris, James Richard
• Granted Patent: US 7,812,758 B2
• Time in Patent Office: Days
• US Class Current: 342/25.F
• CPC Class Codes: G01S 13/003 Bistatic radar systems; Multistatic radar systems
• CPC Class Codes: G01S 13/28 with time compression of received pulses
• CPC Class Codes: G01S 13/90 using synthetic aperture techniques , e.g. synthetic aperture radar [SAR] techniques
• CPC Class Codes: G01S 7/003 Transmission of data between radar, sonar or lidar systems and remote stations
• CPC Class Codes: G01S 7/006 using shared front-end circuitry, e.g. antennas G01S13/765, G01S13/825 take precedence
• CPC Class Codes: G01S 7/28 Details of pulse systems

Abstract

One embodiment of the invention includes a synthetic aperture radar (SAR) system. The system comprises a radar transmitter configured to transmit a combined signal, the combined signal comprising a first signal that is a modulated SAR radar signal and a second signal that is a modulated signal. The system also comprises at least one radar receiver configured to receive a reflected combined signal that comprises a reflected first signal and a reflected second signal, and to demodulate the reflected first and second signals. The reflected first and second signals can correspond to the first and second signals having been reflected from a target. The system further comprises a radar image processor configured to generate a radar image of the target based on signal parameters associated with the reflected first signal and based on information comprised within the reflected second signal.

Claims

1. A synthetic aperture radar (SAR) system comprising:

a radar transmitter configured to transmit a combined signal, the combined signal comprising a first signal that is a modulated SAR radar signal and a second signal that is a modulated signal;

at least one radar receiver configured to receive a reflected combined signal that comprises a reflected first signal and a reflected second signal, the reflected first and second signals corresponding to the first and second signals having been reflected from a target, and to demodulate the reflected first and second signals; and

a radar image processor configured to generate a radar image of the target based on signal parameters associated with the reflected first signal and based on information comprised within the reflected second signal.

2. The system of claim 1, wherein the radar system is configured as one of a bistatic SAR system and a multistatic SAR system.

3. The system of claim 1, wherein the first signal is a linear frequency modulated (FM) chirp signal and the second signal is a spread-spectrum modulated signal.

4. The system of claim 1, wherein the radar transmitter comprises a first amplifier configured to amplify the first signal at a first power level and a second amplifier configured to amplify the second signal at a second power level, the first power level being substantially greater than the second power level, and wherein the first signal and the second signal are modulated orthogonally relative to each other.

5. The system of claim 1, wherein second signal comprises coded communications data in addition to the information comprised within the second signal for transmission of the communications data to at least one RF receiver.

6. The system of claim 1, wherein the first signal comprises a sequential code that defines a transmission sequence of the first signal, and wherein the second signal comprises a pseudo-noise (PN) coded timing sequence that is aligned with the sequential code at the transmitter in a predetermined manner to increase a time-bandwidth product associated with the signal parameters of the reflected first signal at the at least one radar receiver to generate the radar image of the target.

7. The system of claim 6, wherein the time-bandwidth product associated with the signal parameters enables a precise measurement of a time-of-arrival of the reflected first signal at the at least one receiver and a Doppler-shift associated with the reflected first signal.

8. The system of claim 7, wherein the at least one radar receiver is configured to compare the timing sequence with a substantially identical timing sequence of a reference signal to determine the precise time-of-arrival of the reflected first signal.

9. The system of claim 7, wherein the at least one radar receiver is configured to demodulate the reflected second signal and to evaluate a Doppler-shift associated with the reflected second signal to determine the Doppler-shift associated with the reflected first signal.

10. The system of claim 6, wherein the sequential code is a Barker code that comprises coded communications data in addition to defining the transmission sequence of the first signal for transmission of the communications data to at least one RF receiver.

11. A method for generating a radar image of a target in a synthetic aperture radar (SAR) system, the method comprising:

transmitting a combined signal from a transmitter to the target, the combined signal comprising a first signal that is a modulated SAR radar signal and a second signal that is a spread-spectrum modulated signal;

receiving a reflected combined signal at each of at least one radar receiver, the reflected combined signal comprising a reflected first signal and a reflected second signal, the reflected first and second signals corresponding to the first and second signals having been reflected from the target;

demodulating the reflected first and second signals at the at least one radar receiver; and

generating a radar image of the target based on signal parameters associated with the reflected first signal and based on information comprised within the reflected second signal.

12. The method of claim 11, further comprising:

amplifying the first signal to a first power level;

amplifying the second signal to a second power level, the first power level being substantially greater than the second power level; and

modulating the second signal orthogonally relative to the first signal.

13. The method of claim 11, further comprising:

encoding communications data into the second signal; and

transmitting the combined signal to at least one RF receiver.

14. The method of claim 11, further comprising:

encoding the first signal with a sequential code that defines a transmission sequence of the first signal;

encoding the second signal with a pseudo-noise (PN) coded timing sequence that defines a transmission sequence of the second signal;

aligning the sequential code with the PN coded timing sequence at the transmitter in a predetermined manner; and

comparing the timing sequence of the reflected second signal with a substantially identical timing sequence of a reference signal to determine the precise time-of-arrival of the first signal based on the sequential code.

15. The method of claim 14, wherein encoding the first signal comprises encoding the first signal with a sequential Barker code, the method further comprising:

encoding communications data in the sequential Barker code; and

transmitting the first and second signals to at least one RF receiver.

16. The method of claim 11, further comprising comparing a Doppler-shift associated with the reflected second signal to determine the Doppler-shift associated with the reflected first signal at the at least one radar receiver.

17. A synthetic aperture radar (SAR) system comprising:

means for generating a first signal that is a modulated SAR radar signal;

means for generating a second signal that is a spread-spectrum modulated signal, the second signal being orthogonal to the first signal;

means for amplifying the first signal to a first power level;

means for amplifying the second signal to a second power level that is substantially less than the first power level;

means for transmitting a combined signal comprising the first and second signals;

means for receiving a reflected combined signal that comprises a reflected first signal and a reflected second signal, the reflected first and second signals corresponding to the first and second signals having been reflected from a target;

means for demodulating the reflected first signal;

means for demodulating the reflected second signal;

means for processing a phase-history of the reflected first signal based on signal parameters associated with the first signal and based on information comprised within the second signal; and

means for generating a radar image of the target based on the phase-history of the reflected first signal.

18. The system of claim 17, wherein the means for generating the second signal comprises means for encoding communications data in addition to the information comprised within the second signal for transmission of the communications data to at least one RF receiver.

19. The system of claim 17, wherein the means for generating the first signal comprises encoding the first signal with a sequential code that defines a transmission sequence of the first signal, and wherein the means for generating the second signal comprises means for pseudo-noise (PN) encoding a timing sequence, the sequential code and the timing sequence being time-aligned for transmission of the first signal and the second signal.

20. The system of claim 19, wherein the means for processing is further configured to compare the timing sequence with a substantially identical timing sequence of a reference signal to determine the precise time-of-arrival of the reflected first signal.

21. The system of claim 17, wherein the means for processing is further configured to evaluate a Doppler-shift associated with the reflected second signal to determine the Doppler-shift associated with the reflected first signal.

22. The system of claim 17, wherein a signal-to-noise plus interference ratio (SNIR) of the reflected second signal is below approximately 0 dB.