System and method for coherently combining a plurality of radars

• US 20060220951A1
• Filed: 03/16/2006
• Published: 10/05/2006
• Est. Priority Date: 04/04/2005
• Status: Active Grant

• Current Assignee: Raytheon Company (Rtx Corporation)
• Original Assignee: Raytheon Company (Rtx Corporation)
• Inventors: Enzmann, Robert P., Thome, George D., Steudel, Fritz
• Granted Patent: US 7,358,892 B2
• Time in Patent Office: Days
• US Class Current: 342/174
• CPC Class Codes: G01S 13/003 Bistatic radar systems; Multistatic radar systems
• CPC Class Codes: G01S 13/87 Combinations of radar systems, e.g. primary radar and secondary radar
• CPC Class Codes: G01S 13/9058 Bistatic or multistatic SAR
• CPC Class Codes: G01S 7/288 Coherent receivers
• CPC Class Codes: G01S 7/40 Means for monitoring or calibrating
• CPC Class Codes: G01S 7/42 Diversity systems specially adapted for radar

Abstract

Systems and techniques for coherent combining radars include generating a phase and range calibration and initialization values for adjusting a time delay and a phase of a transmitted pulse from one of the radars, resulting in received composite target echoes at each of the radars having contributions from monostatic and bistatic echoes. The method further includes predicting phase and range correction values for further adjusting the time delay and the phase of subsequent radar pulses transmitted by one of the radars to continue to result in received composite target echoes at each of the radars. The method further includes coherently summing the composite target echoes.

Claims

1. A method of calibrating a plurality of radars, comprising:

selecting a reference radar from among the plurality of radars;

selecting one or more pairs of radars, each one of the pairs of radars including the reference radar and a respective paired radar from among the plurality of radars;

generating calibration values associated with the reference radar and with the paired radar;

generating initialization values associated with the reference radar and with the paired radar;

transmitting an adjusted signal with the paired radar and an unadjusted signal with the reference radar, the adjusted signal generated in accordance with the initialization values and the calibration values;

receiving a first composite signal with the reference radar and a second composite signal with the paired radar, the first and second composite signals associated with the adjusted signal and the unadjusted signal; and

coherently summing the first composite signal and the second composite signal to provide a final signal.

2. The method of claim 1, wherein the generating calibration values includes:

transmitting one or more calibration signals with the reference radar and one or more calibration signals with the paired radar;

receiving respective bistatic target echoes with the reference radar;

receiving respective bistatic target echoes with the paired radar, wherein the reference radar bistatic target echoes and the paired radar bistatic target echoes are associated with the one or more calibration signals transmitted by the reference radar and with the one or more calibration signals transmitted by the paired radar;

generating a phase calibration relationship in accordance with a phase between the bistatic target echoes received by the reference radar and the bistatic target echoes received by the paired radar; and

generating a range calibration relationship in accordance with a time delay between the bistatic target echoes received by the reference radar and the bistatic target echoes received by the paired radar.

3. The method of claim 1, wherein the generating initialization values includes:

transmitting one or more initialization signals with the reference radar and one or more initialization signals with the paired radar;

receiving respective monostatic and bistatic target echoes with the reference radar;

receiving respective monostatic and bistatic target echoes with the paired radar, wherein the reference radar monostatic and bistatic target echoes and the paired radar monostatic and bistatic target echoes are associated with the one or more initialization signals transmitted by the reference radar and with the one or more initialization signals transmitted by the paired radar;

generating a phase initialization relationship in accordance with a phase between the monostatic and bistatic target echoes received by the reference radar and a phase between the monostatic and bistatic target echoes received by the paired radar; and

generating a range initialization relationship in accordance with a time delay between monostatic and bistatic target echoes received by the reference radar and a time delay between the monostatic and bistatic target echoes received by the paired radar.

4. The method of claim 3, wherein at least one of the phase initialization relationship and the range initialization relationship are generated in association with a least squares linear fit.

5. The method of claim 3, further including predicting a range initialization value associated with the range initialization relationship and a phase initialization value associated with the phase initialization relationship.

6. The method of claim 3, wherein the transmitting the adjusted signal with the paired radar and the unadjusted signal with the reference radar includes:

predicting a phase initialization value associated with the phase initialization relationship;

predicting a range initialization value associated with the range initialization relationship; and

adjusting a relative phase and a time delay of the paired radar relative to the reference radar in accordance with the phase initialization value and the range initialization value.

7. The method of claim 1, wherein the coherently summing the first composite signal and the second composite signal includes:

measuring a phase between the first composite signal and the second composite signal;

aligning a relative phase of the first and second composite signals to provide an aligned first composite signal and an aligned second composite signal in accordance with the measured phase between the first composite signal and the second composite signal; and

adding the aligned first and second composite signals.

8. The method of claim 7, wherein the coherently summing further includes:

measuring a residual phase error according to the phase between the first composite signal and the second composite signal;

generating a composite signal phase relationship in accordance with the residual phase error; and

predicting a composite phase value from the composite signal phase relationship.

9. The method of claim 8, wherein the composite signal phase relationship comprises an alpha function.

10. The method of claim 8, further including:

transmitting a second adjusted signal with the paired radar and the unadjusted signal with the reference radar, the second adjusted signal generated in accordance with the initialization values, the calibration values, and the composite phase value;

receiving a third composite signal with the reference radar and a fourth composite signal with the paired radar, the third and fourth composite signals associated with the second adjusted signal and the unadjusted signal; and

coherently summing the third and fourth composite signals to provide a second final signal.

11. The method of claim 10, wherein the coherently summing the third and fourth composite signals includes:

measuring a phase between the third composite signal and the fourth composite signal;

aligning a relative phase of the third and fourth composite signals to provide an aligned third composite signal and an aligned fourth composite signal in accordance with the measured phase between the third composite signal and the fourth composite signal; and

adding the aligned third and fourth composite signals.

12. The method of claim 11, wherein the coherently summing the third and fourth composite signals further includes:

measuring a second residual phase error according to the phase between the third composite signal and the fourth composite signal;

updating the composite signal phase relationship in accordance with the second residual phase error; and

predicting an updated composite phase value from the updated composite signal phase relationship.

13. Apparatus to calibrate a plurality of radars, comprising:

an association processor to associate at least one respective target track provided by each of a pair of radars from among the plurality of radars including a reference radar and a paired radar;

a calibration processor coupled to the association processor to provide calibration values associated with the pair of radars;

an initialization processor coupled to the calibration processor to provide initialization values associated with the pair of radars; and

a coherence maintenance processor coupled to the initialization processor to adjust at least one of a first signal transmitted by the reference radar and a second signal transmitted by the paired radar in accordance with the initialization values and with the calibration values, and to coherently sum a first composite signal received by the reference radar with a second composite signal received by the paired radar.

14. The apparatus of claim 13, wherein the calibration processor includes:

a phase calibration processor coupled to the association processor to generate a phase calibration relationship in accordance with a phase between bistatic target echoes received by the reference radar and by the paired radar and to generate a phase calibration value; and

a range calibration processor coupled to the association processor to generate a range calibration relationship in accordance with a time delay between the bistatic target echoes received by the reference radar and by the paired radar and to generate a range calibration value.

15. The apparatus of claim 13, wherein the initialization processor includes:

a phase prediction processor coupled to the calibration processor to generate a phase initialization relationship in accordance with a phase between monostatic and bistatic target echoes received by the reference radar and a phase between monostatic and bistatic target echoes received by the paired radar; and

a range prediction processor coupled to the calibration processor to generate a range initialization relationship in accordance with a time delay between the monostatic and bistatic target echoes received by the reference radar and a time delay between the monostatic and bistatic target echoes received by the paired radar.

16. The apparatus of claim 15, wherein the phase prediction processor and the range prediction processor each comprise a respective least squares fit processor.

17. The apparatus of claim 15, wherein the phase prediction processor is further to generate a phase initialization value in accordance with the phase initialization relationship and to generate a range initialization value in accordance with the range initialization relationship.

18. The apparatus of claim 13, wherein the coherence maintenance processor includes:

a measurement processor to measure a phase between the first composite signal and the second composite signal;

a phase rate filer coupled to the measurement processor to generate a composite signal phase relationship; and

a prediction processor coupled to the phase rate filter to predict a composite phase value in accordance with the composite signal phase relationship.

19. The apparatus of claim 18, wherein the phase rate filter comprises an alpha function filter.

20. The apparatus of claim 18, wherein the phase rate filter comprises a Kalman filter.

21. The apparatus of claim 18, wherein the phase rate filter comprises a least squares fit processor.

22. Apparatus to calibrate a plurality of radars, comprising:

an association processor to associate at least one respective target track provided each of a pair of radars from among the plurality of radars including a reference radar and a paired radar;

a calibration processor coupled to the association processor, including;

a phase calibration processor to generate a phase calibration relationship between the bistatic target echoes received by the reference radar and by the paired radar and to generate a phase calibration value; and

a range calibration processor to generate a range calibration relationship between the bistatic target echoes received by the reference radar and by the paired radar and to generate a range calibration value;

an initialization processor coupled to the calibration processor, including;

a phase prediction processor coupled to the calibration processor to generate a phase initialization relationship in accordance with a phase between monostatic and bistatic target echoes received by the reference radar and a phase between monostatic and bistatic target echoes received by the paired radar; and

a range prediction processor coupled to the calibration processor to generate a range initialization relationship in accordance with a time delay between the monostatic and bistatic target echoes received by the reference radar and a time delay between the monostatic and bistatic target echoes received by the paired radar; and

a coherence maintenance processor coupled to the initialization processor to adjust at least one of a first signal transmitted by the reference radar and a second signal transmitted by the paired radar in accordance with the phase initialization value, the range initialization value, the phase calibration value, and the range calibration value, and to coherently sum a first composite signal received by the reference radar with a second composite signal received by the paired radar, the coherency processor including;

a measurement processor to measure a phase between the first composite signal and the second composite signal;

a phase rate filer coupled to the measurement processor to generate a composite signal phase relationship; and

a prediction processor coupled to the phase rate filter to predict a composite phase value in accordance with the composite signal phase relationship.