Method and system for use of GPS disciplined oscillators for coherent timing reference in distributed radar systems

• US 8,922,421 B2
• Filed: 12/10/2010
• Issued: 12/30/2014
• Est. Priority Date: 12/10/2009
• Status: Expired due to Fees

• Current Assignee: Lockheed Martin Corporation (Martin Marietta Corporation)
• Original Assignee: Lockheed Martin Corporation (Martin Marietta Corporation)
• Inventors: Pomietlasz, Daniel J.
• Primary Examiner(s): Sotomayor, John B
• Assistant Examiner(s): WINDRICH, MARCUS E
• Application Number:
  US12/965,458
• Publication Number:
  US 20120188125A1
• Time in Patent Office: 1,481 Days
• Field of Search: 342/89
• US Class Current: 342/59
• CPC Class Codes: G01S 13/87 Combinations of radar systems, e.g. primary radar and secondary radar
• CPC Class Codes: G01S 19/14 specially adapted for specific applications

Abstract

An active electronically scanned array radar system and method uses a coherent, stable timing reference to transmit phase synchronized radar signals from a plurality of receiver/exciter elements. A global positioning system (GPS) carrier phase disciplined oscillator receives the GPS carrier signal at a GPS receiver. The GPS carrier contains phase and timing information to phase synchronize the local clock with the GPS carrier to produce a reference clock signal. The reference clock signal is used to synchronize a frequency synthesizer oscillator clock and generate a stable timing reference signal at a frequency significantly greater than the reference clock frequency. The stable timing reference is used to transmit radar signals in a receiver/exciter pair, the radar signals phase synchronized with the GPS carrier signal. Each receiver/exciter element generates its own stable timing reference based on a common GPS carrier. The radar signals from the plurality of receiver/exciter elements use a common clock without need of a physical distribution mechanism.

Claims

1. A method of providing a coherent, synchronized timing reference to a plurality of receiver/exciter pairs of a radar array, comprising:

receiving, at each receiver/exciter pair, a global positioning system (GPS) carrier signal directly from a GPS satellite, the GPS carrier signal including phase and timing information;

generating, at each receiver/exciter pair, a local clock signal using a local oscillator;

phase synchronizing the local clock signal to the received GPS carrier signal to produce a reference clock signal; and

generating a stable timing reference signal based on the local clock signal and the reference clock signal, the stable timing reference signal being phase synchronized to the received GPS carrier signal.

2. The method of claim 1, wherein the stable timing reference has a frequency greater than the frequency of the reference clock signal.

3. The method of claim 2, wherein the reference clock signal has a frequency of about 10 MHz and a phase accuracy of within about 10 picoseconds of said GPS carrier signal.

4. The method of claim 3, wherein the GPS carrier signal is about 1.5 GHz.

5. The method of claim 4, wherein the stable timing reference has a frequency of about 3 GHz and a phase accuracy of within about 33 femtoseconds of said GPS carrier signal.

6. The method of claim 1, further comprising transmitting or receiving from at least one of the receiver/exciter pairs, radar signals synchronized to the stable timing reference based on the received GPS carrier signal.

7. The method of claim 1, wherein the local oscillator is a rubidium oscillator.

8. The method of claim 1, wherein the local oscillator is an oven controlled crystal oscillator (OCXO).

9. The method of claim 1, wherein the local oscillator is a chip scale atomic clock (CSAC) oscillator.

10. The method of claim 1, further comprising generating a control signal, the control signal indicative of a selected GPS satellite in a GPS satellite constellation, from which the GPS carrier signal is received.

11. A radar system having a plurality of receiver/exciter elements in a radar array for transmitting or receiving phase synchronized radar signals, wherein each receiver/exciter element includes:

a global positioning system (GPS) carrier phase disciplined oscillator (GCPDO) apparatus comprising;

a GPS receiver configured to receive a GPS carrier signal directly from a GPS satellite;

a local oscillator operatively coupled to said GPS receiver; and

a timing processor responsive to the output of the GPS receiver and to the local oscillator for providing a common clock reference based on the GPS carrier signal, wherein each said common clock reference is coherent with respect to all other receiver/exciter element common clock references; and

a synthesizer configured to generate radar signals based on the common clock reference, the radar signals being phase synchronized with the received GPS carrier signal.

12. The system of claim 11, wherein said synthesizer is responsive to the coherent common clock reference from said timing processor and to said local oscillator for providing a stable timing reference to a corresponding exciter/receiver element based on the received GPS carrier.

13. The system of claim 11, wherein the timing processor is configured to receive phase and timing data contained in the GPS carrier signal, and to output a control signal to the GPS receiver.

14. The system of claim 13, wherein the control signal includes information about which GPS satellite in a GPS satellite constellation the GPS receiver should receive the GPS carrier signal.

15. The system of claim 11, wherein the local oscillator is in communication with the timing processor and the GPS receiver and configured to provide a local clock signal.

16. The system of claim 11, wherein the timing processor receives the GPS phase and timing data and the local clock signal and outputs a reference clock signal that is phase synchronized to the received GPS signal.

17. The system of claim 11, wherein the reference clock signal has a frequency of 10 MHz and is phase accurate to the GPS carrier signal with 10 picoseconds.

18. The system of claim 11, wherein the local oscillator is a rubidium oscillator.

19. The system of claim 11, wherein the local oscillator is an oven controlled crystal oscillator (OCXO).

20. The system of claim 11, wherein the local oscillator is a chip scale atomic clock (CSAC) oscillator.

21. The system of claim 12, wherein the stable timing reference is at a frequency greater than the frequency of the reference clock signal.

22. The system of claim 11, wherein the GCPDO is configured to generate the reference clock signal based on the received GPS carrier signal periodically at a predetermined time interval.

23. The system of claim 11, wherein the stable timing reference is phase synchronized to a common GPS carrier signal, the GPS carrier signal received by a plurality of other receiver/exciter elements in the radar array.

24. A distributed active electronically scanned array (AESA) radar system comprising a plurality of AESA radar arrays, each AESA radar array remotely positioned relative to the other said AESA radar arrays, each said AESA radar array comprising a plurality of receiver/exciter elements, the distributed AESA radar system comprising:

for each receiver/exciter element;

a global positioning system (GPS) carrier phase disciplined oscillator (GCPDO) configured to receive a GPS carrier signal directly from a GPS satellite and generate a stable timing reference, the stable timing reference phase synchronized to all other receiver/exciter elements and the received GPS carrier signal; and

wherein said receiver/exciter element is configured to transmit or receive radar signals based on the stable timing reference.

25. The distributed AESA radar system of claim 24, further comprising a controller for each AESA radar array, said controller configured to receive control information from a central control.

26. The distributed AESA radar system of claim 24, further comprising for each AESA radar array, a communications module configured to transmit location information relating to the AESA radar array to the central control.

27. The distributed AESA radar system of claim 25, wherein the controller is further configured to receive from the central control, at least one of, information relating to AESA radar systems selected for transmitting radar signals at a target, information relating to the location of an AESA radar system selected for transmitting radar signals at a target, information relating to a location of a target, and information relating to a time when radar signals will be transmitted at a target.

28. The distributed AESA radar system of claim 27, further comprising for each AESA receiver/exciter element, a processor configured to receive the control information from the central control and delay a transmission by the AESA receiver/exciter element such that radar signals transmitted by the AESA receiver/exciter element arrive at a target simultaneously with radar signals transmitted at the target by other AESA radar arrays.

29. A method of synchronizing a plurality of receiver/exciter pairs of a radar array, the method comprising the steps of:

at each receiver/exciter pair of said radar array;

receiving a Global Positioning System (GPS) carrier signal from a GPS satellite;

receiving timing information encoded on said GPS carrier signal and determining phase information relating to the GPS carrier signal;

generating a local clock signal at the receiver/exciter pair;

phase synchronizing the local clock signal with the GPS carrier signal based on the phase information of the GPS carrier signal to produce a reference clock signal, wherein the phase synchronization is performed by each receiver/exciter pair independently of each other receiver/exciter pair;

generating a stable timing reference signal based on the reference clock signal, the stable timing reference signal having a frequency greater than the reference clock signal frequency, and

wherein the stable timing reference signal is coherent with a stable timing reference signal of each other receiver/exciter pair based on the GPS carrier signal received at each receiver/exciter.