Fiber optic feed and phased array antenna

• US 5,365,239 A
• Filed: 11/06/1991
• Issued: 11/15/1994
• Est. Priority Date: 11/06/1991
• Status: Expired due to Fees

• Current Assignee: the united states of america as represented by the secretary of the navy
• Original Assignee: the united states of america as represented by the secretary of the navy
• Inventors: Stilwell, P. Denzil Jr.
• Primary Examiner(s): Blum, Theodore M.
• Application Number:
  US07/788,704
• Time in Patent Office: 1,105 Days
• Field of Search: 342/368, 342/371, 342/372, 342/54, 342/156, 342/157, 342/424
• US Class Current: 342/368
• CPC Class Codes: H01Q 3/2676 Optically controlled phased array

Abstract

A fiber optic feed includes an optical circuit for providing at least one optical output signal modulated according to an RF source and an antenna interface for demodulating the at least one optical output signal and communicating with an antenna, wherein the optical circuit includes a coherent light source, an interferometer driven by the coherent light source for synthesizing a plurality of independently controlled planar beams, an optic modulator for frequency modulating at least one of the independently controlled planar beams according to the RF source and an optic pickup for producing the at least one optical output signal according to a superposition of the plurality of independently controlled planar beams, wherein the interferometer includes at least one beam deflector for angularly deflecting at least one of the plurality of independently controlled beams according to a beam control command.

A phased array antenna includes an optical circuit for providing at least one optical output signal modulated according to an RF source and an antenna module for demodulating the at least one optical output signal and communicating with at least one RF radiating element, wherein the optical circuit includes a coherent light source, an interferometer driven by the coherent light source for synthesizing a plurality of independently controlled planar beams, an optic modulator for frequency modulating at least one of the independently controlled planar beams according to the RF source, and an optic pickup for producing the at least one optical output signal according to a superposition of the plurality of independently controlled planar beams, wherein the interferometer includes at least one beam deflector for angularly deflecting at least one of the plurality of independently controlled planar beams according to a beam control command.

Claims

1. A fiber optic feed comprising:

optical circuit means for providing at least one optical output signal modulated according to an RF source; and

antenna interface means for demodulating said at least one optical output signal and communicating with an antenna;

wherein said optical circuit means comprises;

a coherent light source;

interferometer means driven by said coherent light source for synthesizing a plurality of independently controlled beams;

optic modulating means for frequency modulating at least one of said independently controlled beams according to said RF source; and

optic pickup means for producing said at least one optical output signal according to a superposition of said plurality of independently controlled beams.

2. The fiber optic feed of claim 1, wherein said optic modulating means comprises a non-deflecting electro-optic modulator.

3. The fiber optic feed of claim 1, wherein said optic modulating means comprises a non-deflecting acousto-optic modulator.

4. The fiber optic feed of claim 1, wherein said interferometer means comprises beam deflecting means for angularly deflecting at least one of said plurality of independently controlled beams according to a beam control command.

5. The fiber optic feed of claim 4, wherein said optic pickup means comprises at least one pickup element positioned with respect to said interferometer means so as to collect a spatial portion of said superposition of said plurality of independently controlled beams and so that at any time a difference in a phase of one beam relative to a phase of another beam depends upon said position of said at least one pickup element.

6. The fiber optic feed of claim 5, wherein said antenna interface means comprises detector means for detecting at least one RF signal having a frequency within a bandwidth about a frequency of said RF source.

7. The fiber optic feed of claim 4, wherein said beam deflecting means comprises at least one non-modulating acousto-optic beam deflector.

8. The fiber optic feed of claim 4, wherein said beam deflecting means comprises a mirror.

9. The fiber optic feed of claim 7, wherein said beam control command comprises a signal having a frequency determinative of a desired beam deflection angle.

10. The fiber optic feed of claim 4, wherein:

said optic pickup means comprises a plurality of optic pickup elements arranged in an array, each optic pickup element positioned with respect to said interferometer means so as to collect a spatial portion of said superposition of said plurality of independently controlled planar beams and so that at any time a difference in a phase of one beam relative to a phase of another beam depends upon a position of said each optic pickup element within said array;

said at least one optical output signal comprises a plurality of optical output signals, each optical output signal being derived from said spatial portion collected by a corresponding optic pickup element; and

said antenna interface means comprises an array of detector elements, each detector element corresponding to a respective optic pickup element.

11. The fiber optic feed of claim 10, wherein said array of pickup elements is a planar array.

12. The fiber optic feed of claim 10, wherein one of said plurality of indpendently controlled beams is non-planar to compensate for a conformal array of RF radiating elements.

13. The fiber optic feed of claim 10, wherein each of said detector elements comprises a detector corresponding to a respective pickup element for producing a corresponding RF signal within a frequency bandwidth about a frequency of said RF.

14. The fiber optic feed of claim 13, wherein each of said RF signals has a phase relative to at least one other RF signal based on a position of an optic pickup element corresponding to said each RF signal relative to a position of an optic pickup element corresponding to said at least one other RF signal.

15. The fiber optic feed of claim 1, wherein said interferometer means comprises at least one coherent light amplifier, each coherent light amplifier being disposed in a corresponding one of said plurality of independently controlled beams.

16. The fiber optic feed of claim 15, wherein said optic modulating means is disposed in at least one of said plurality of independently controlled beams between a respective one of said at least one coherent light amplifier and said coherent light source so that an input to said coherent light amplifier is a modulated light beam.

17. The fiber optic feed of claim 16, wherein said modulation means comprises a non-deflecting acousto-optic modulator.

18. The fiber optic feed of claim 16, wherein said modulation means comprises a conventional acousto-optic modulator so that said modulation means deflects light from said coherent light source according to a frequency of said RF source so as to deflect said light from said coherent light source into said input to said coherent light amplifier.

19. The fiber optic feed of claim 15, wherein:

said at least one coherent light amplifier comprises a plurality of coherent light amplifiers;

said modulating means comprises at least one non-deflecting modulator, each modulator having an input which is driven by an output of a corresponding one of said plurality of coherent light amplifiers; and

said interferometer means further comprises at least one beam deflector, an input to which is driven by a corresponding output of said at least one non-deflecting modulator and a combining means for combining outputs of said at least one beam deflector.

20. The fiber optic feed of claim 4, wherein:

said beam deflecting means comprises at least one conventional acousto-optic beam deflector; and

said beam control command comprises a signal having plural frequency components so that said at least one of said plurality of independently controlled beams in which said beam deflecting means is disposed is split and deflected into plural beam components having deflection angles corresponding to and defined by respective ones of said plural frequency components.

21. The fiber optic feed of claim 4, wherein:

said plurality of independently controlled beams comprises a reference beam, a main beam and at least one auxiliary beam;

said beam deflecting means comprises a reference beam deflector disposed in said reference beam, a main beam deflector disposed in said main beam, at least one auxiliary beam deflector disposed in corresponding beams of said at least one auxiliary beam, and at least one amplitude/phase control means for controlling amplitudes and phases of beams passing through corresponding beam deflectors of said at least one auxiliary beam deflector so that said controlled amplitudes and phases are controlled relative to an amplitude and phase of said main beam as deflected by said main beam deflector.

22. The fiber optic feed of claim 21, wherein said reference beam deflector, said main beam deflector and each of said auxiliary beam deflectors are conventional acousto-optic beam deflectors, said reference beam deflector being so oriented with respect to each of said main beam deflector and each auxiliary beam deflector so as to deflect said reference beam in a same plane and in an opposite direction to each of the other beam deflectors, and all beam deflectors being so oriented as to modulate frequencies of all beams to one of increase and decrease said frequencies by equal amounts.

23. The fiber optic feed of claim 21, wherein said beam deflecting means further comprises:

pointing means for further deflecting each of said at least one auxiliary beam.

24. The fiber optic feed of claim 23, wherein said pointing means comprises a non-modulating acousto-optic beam deflector.

25. The fiber optic feed of claim 4, wherein said at least one independently controlled beam comprises two beams, and wherein said beam deflecting means comprises two beam deflectors, each beam deflector disposed in separate beams.

26. The fiber optic feed of claim 15, wherein a phase of an output of said at least one coherent light amplifier is phased-locked to a phase of an output of said coherent light source.

27. The fiber optic feed of claim 4, wherein said beam deflecting means comprises two beam deflectors disposed in said at least one of said plurality of independently controlled beams and oriented so that a first beam deflector deflects said at least one beam in a first direction and so that a second beam deflector deflects said at least one beam in a second direction substantially orthogonal to said first direction.

28. The fiber optic feed of claim 4, wherein:

said interferometer means further comprises splitter means for producing a plurality of identical phase gradient beams, each of said phase gradient beams being based on said superposition of said plurality of independently controlled beams; and

said fiber optic pickup means comprises at least one pickup element positioned with respect to said splitter means in each of said plurality of identical phase gradient beams.

29. The fiber optic feed of claim 10, wherein said interferometer means further comprises beam expander/compressor means for under-illuminating said array of optic pickup elements and beam displacer means for displacing a phase center of an illuminated portion of said array of optic pickup elements.

30. The fiber optic feed of claim 4, wherein said beam deflecting means comprises a first pair of beam deflectors disposed in a first one of said plurality of independently controlled beams and oriented so that a first beam deflector of said first pair deflects said first one of said plurality of beams in a first direction and so that a second beam deflector of said first pair deflects said first one of said plurality of beams in a second direction substantially orthogonal to said first direction;

and a second pair of beam deflectors disposed in a second one of said plurality of independently controlled beams and oriented so that a first beam deflector of said second pair deflects said second one of said plurality of beams in said first direction and so that a second beam deflector of said second pair deflects said second one of said plurality of beams in said second direction.

31. The fiber optic feed of claim 30, wherein:

said first beam deflector of said first pair cooperates with said first beam deflector of said second pair to modulate respective first and second beams to one of increase and decrease a frequency of said first and second beams by equal amounts; and

said second beam deflector of said first pair cooperates with said second beam deflector of said second pair to modulate respective first and second beams to one of increase and decrease a frequency of said first and second beams by equal amounts.

32. The fiber optic feed of claim 1, wherein the plurality of independently controlled beams are planar.

33. The fiber optic feed of claim 1, wherein the plurality of independently controlled beams are non-planar.

34. A phased array antenna comprising:

optical circuit means for providing at least one optical output signal modulated according to an RF source; and

module means for demodulating said at least one optical output signal and communicating with at least one RF radiating element;

wherein said optical circuit means comprises;

a coherent light source;

interferometer means driven by said coherent light source for synthesizing a plurality of independently controlled planar beams;

optic modulating means for frequency modulating at least one of said independently controlled planar beams according to said RF source; and

optic pickup means for producing said at least one optical output signal according to a superposition of said plurality of independently controlled planar beams.