Optically frequency generated scanned active array

• US 20040090365A1
• Filed: 11/13/2002
• Published: 05/13/2004
• Est. Priority Date: 11/13/2002
• Status: Abandoned Application

• Current Assignee: Raytheon Company (Rtx Corporation)
• Original Assignee: Raytheon Company (Rtx Corporation)
• Inventors: Wilkinson, Steven R., Lee, Jar J, Rosen, Robert A., Krikorian, Kapriel V., Newberg, Irwin L.
• Application Number:
  US10/294,863
• Publication Number:
  US 20040090365A1
• Time in Patent Office: Days
• US Class Current: 342/368
• CPC Class Codes: H01Q 13/28 comprising elements constituting electric discontinuities and spaced in direction of wave propagation, e.g. dielectric elements or conductive elements forming artificial dielectric
• CPC Class Codes: H01Q 3/22 varying the orientation in accordance with variation of frequency of radiated wave
• CPC Class Codes: H01Q 3/2676 Optically controlled phased array

Abstract

A the system for scanning an antenna array (26) adapted for use with active radar arrays. A first mechanism (14, 18, 20, 24) generates an optical signal oscillating at a predetermined frequency. A second mechanism (32, 34) employs the optical signal to derive feed signals, which have predetermined phase relationships. A third mechanism (22) receives the feed signals and radiates corresponding transmit signals in response thereto to the antenna array (26) to steer the antenna array (26) in accordance with the predetermined phase relationships. In a specific embodiment, the transmit signals are microwave frequency signals. The first mechanism (14, 18, 20, 24) includes a first optical oscillator (18) and a second optical oscillator (20) that feed a first optical manifold (32) and a second optical manifold (34), respectively, of the second mechanism (32, 34). The first optical manifold (32) includes an optical feed that provides differential delays to a signal output from the first optical oscillator (18) via optical feeds of different lengths to provide a progressive phase corresponding to the predetermine phase relationships.

Claims

1. A system for scanning an antenna array comprising:

first means for generating an optical signal oscillating at a predetermined frequency;

second means for employing said optical signal to derive feed signals having predetermined phase relationships; and

third means for receiving said feed signals and radiating corresponding transmit signals in response thereto to said antenna array to steer said array.

2. The system of claim 1 wherein said first means includes a frequency-tunable optical oscillator.

3. The system of claim 2 wherein said frequency-tunable optical oscillator includes an RF phase shifter to facilitate changing an output frequency of said optical oscillator.

4. The system of claim 2 wherein said optical signal is a radio frequency signal modulated on an optical carrier.

5. The system of claim 4 wherein said optical oscillator includes an optical feedback signal that passes through a delay line and to a detector, said detector converting said optical feedback signal to a radio frequency feedback signal that is fed back to an optical modulator of said optical oscillator.

6. The system of claim 5 wherein said first means includes plural of said optical oscillators including a first optical oscillator and a second optical oscillator that feed a first optical manifold and a second optical manifold, respectively, of said second means.

7. The system of claim 6 wherein said first optical oscillator and said second optical oscillator track each other in frequency with a predetermined frequency offset in response to control signals received from a controller when said system scans said antenna array in a predetermined dimension.

8. The system of claim 7 wherein a relationship between a first frequency generated by said first optical oscillator and a second frequency generated by said second optical oscillator is such that mixing of said first frequency and said second frequency produces a constant output frequency that is independent of changes in said first frequency, which is a scanning frequency of said antenna.

9. The system of claim 7 wherein said first optical manifold includes an optical feed that provides differential delays to a signal output from said first optical oscillator via optical feeds of different lengths so that resultant different optical delays result in a progressive phase required for antenna phase scanning.

10. The system of claim 9 wherein said second optical manifold includes a corporate feed having optical feeds of equal lengths so that changes in frequency of optical signals passing through said second optical manifold do not affect azimuth or elevation scanning effected via signals passing through said first optical manifold.

11. The system of claim 10 wherein said second optical manifold includes an optical radio frequency phase shifter for selectively adding coding to an optical signal passing through said second optical manifold.

12. The system of claim 11 wherein said antenna array is a continuous transverse stub array.

13. The system of claim 2 wherein said third means includes a transmit/receive module.

14. The system of claim 13 wherein said transmit/receive module includes a photodiode detector mixer that outputs sum and difference radio frequencies.

15. The system of claim 14 wherein said transmit/receive module includes a high pass filter for selecting said sum frequencies as output.

16. The system of claim 15 wherein said transmit/receive module is configured so that said sum frequencies provide phases to steer said antenna array and provide phases that are applied to receive signals to facilitate coherent adding of said receive signals.

17. The system of claim 16 wherein a mixing signal derived from said sum frequencies includes frequencies associated with an output of said second optical manifold.

18. The system of claim 15 wherein said system is a radar system that further includes a sum manifold for coherently summing said receive signals to provide a sum radar receive signal in response thereto.

19. The system of claim 18 wherein said radar system further includes an analog-to-digital converter for converting said sum radar receive signal to a digital signal for use by a radar system controller.

20. The system of claim 2 wherein said optical oscillator feeds said antenna array through an optical manifold included in said second means.

21. The system of claim 20 wherein said optical oscillator modulates microwave frequency signals on an optical carrier.

22. The system of claim 21 wherein said optical manifold incorporates differential delays to generate signals to beam point or steer said active array.

23. The system of claim 22 wherein said optical manifold includes a differential feed that includes fiber optic waveguides of different lengths to achieve said differential delays.

24. The system of claim 23 wherein said antenna array is a continuous transverse stub active antenna array.

25. The system of claim 24 further including scanning means for scanning said active array in both azimuth and elevation without individual phase shifters.

26. The system of claim 25 wherein said scanning means includes one or more serpentine lines.

27. The system of claim 25 wherein said means for scanning further includes means for changing a frequency output from said optical oscillator to control a progressive phase in said active array feed to beam steer said array.

28. The system of claim 27 wherein said optical manifold includes a corporate feed for facilitating scanning said continuous transverse stub active array in elevation and includes said differential feed for scanning said active array in azimuth.

29. The system of claim 27 wherein said system includes a transmit module with metamorphic high-energy mobility transistors (MHEMT).

30. The system of claim 29 wherein said transmit module includes one or more microelectromechanical switches for duplexing said transmit and receive signals.

31. The system of claim 27 further including means for employing a transmit signal to demodulate an antenna receive signal.

32. An radar system comprising:

an antenna array;

an optical oscillator that generates an optical signal oscillating at a predetermined frequency;

an optical manifold that employs said optical signal to derive feed signals having progressive phase relationships; and

optical transmit modules that each receive one of said feed signals and output corresponding electrical signals in response thereto to said antenna array.

33. The system of claim 32 wherein said optical oscillator is a voltage tuned oscillator that may change a frequency of said optical signal in response to a control signal.

34. The system of claim 33 further including a controller providing said control signal and for steering said array by controlling the frequency of said optical signal.

35. The system of claim 34 further including on or more serpentine lines between said optical transmit modules and said antenna array.

36. The system of claim 34 wherein said predetermined frequency is a microwave frequency or a millimeter wave frequency.

37. The system of claim 34 further including means for receiving a return signal and demodulating said return signal based on said transmit signal.

38. The system of claim 37 wherein said optical manifold includes a differential delay feed having plural optical fibers of different lengths, said different lengths sufficient to achieve progressive phase relationships between optical outputs of said plural fibers to facilitate steering of said antenna array.

39. The system of claim 38 wherein said antenna array is a continuous transverse stub array.

40. The system of claim 39 wherein said optical manifold further includes a corporate feed having optical fibers of equal lengths for providing corporate optical outputs sufficient to scan said continuous transverse stub array in elevation.

41. The system of claim 40 wherein said corporate optical outputs have coding modulated thereon.

42. The system of claim 41 wherein said coding is pulse compression coding.

43. The system of claim 32 wherein said antenna array is an active array, and wherein said optical manifold includes a first optical manifold for scanning said active array in a first dimension and a second manifold for scanning said active array in a second dimension.

44. The system of claim 43 wherein said first dimension is azimuth, and wherein said second dimension is elevation.

45. The system of claim 44 wherein said radar system lacks phase shifters for beam steering said active antenna array on a transmit or a receive path.

46. The system of claim 44 wherein said optical oscillator includes a first optical oscillator and a second optical oscillator for feeding said first optical manifold and said second optical manifold, respectively.

47. The system of claim 46 wherein said radar system further includes a receive manifold and a control manifold for receiving return signals and controlling said antenna array in response thereto, respectively.

48. A method for scanning an antenna array having plural elements comprising the steps of:

generating an optical signal oscillating at a predetermined frequency;

employing said optical signal to derive feed signals having a predetermined phase relationships; and

receiving said feed signals and outputting corresponding electrical signals in response thereto to said antenna array.