Chirped fiber grating beamformer for phased array antennas

• US 6,137,442 A
• Filed: 04/01/1998
• Issued: 10/24/2000
• Est. Priority Date: 04/01/1998
• Status: Expired due to Fees

• Current Assignee: The United States of America As Represented By The Secretary of Agriculture
• Original Assignee: the united states of america as represented by the secretary of the navy
• Inventors: Frankel, Michael, Roman, Jose E., Esman, Ronald D.
• Primary Examiner(s): Tarcza, Thomas H.
• Assistant Examiner(s): PHAN, DAO LINDA
• Application Number:
  US09/058,352
• Time in Patent Office: 937 Days
• Field of Search: 342/368, 342/375, 359/140, 385/37
• US Class Current: 342/375
• CPC Class Codes: H01Q 3/2682 Time delay steered arrays
• CPC Class Codes: H01Q 3/2688 using acoustic or magnetostatic wave devices

Abstract

A new fiber optic based beamforming architecture for a time steered phasedrray antenna based on chirped fiber gratings. All of the gratings are identical in length and period chirp so that they all have the same dispersion, thus at a given optical wavelength they have the same time delay. In a preferred embodiment an optical signal is modulated with an RF signal. The RF modulated optical is split and a portion propagates through a length of fiber to a photodetector feeding an antenna array. The second portion of the optical signal is routed through a circulator, which feeds the optical signal to a chirped fiber grating. The grating reflects and delays the optical signal back to the circulator which routes the reflected optical signal to a second coupler. The amount of delay incurred is determined by the grating dispersion and the wavelength of the optical source. The second splits the time delayed optical signal, passing a portion of the time delayed optical signal to the second antenna element and the other portion to other circulators and ultimately to other antenna elements comprising the antenna array. The time delay imposed on the optical signal through the use of chirped fiber gratings controls the relative timing between the antenna elements, thus allowing one to steer the antenna by changing the wavelength of the optical signal.

Claims

1. A fiber optic based phased array antenna comprising:

means for producing an optical signal,

means for modulating said optical signal with an rf signal,

means for dividing said modulated optical signal, said means for dividing said optical signal splitting said optical signal into a plurality of component optical signals,

means for time delaying at least one of said plurality of component optical signals comprising chirped fiber gratings of identical length and chirp,

an antenna array, said antenna array comprising a plurality of radiating elements,

means for coupling each of said plurality of optical signals with a corresponding radiating element;

wherein each of said radiating elements produce an electromagnetic signal, the timing of said electromagnetic signal produced by each of said radiating elements being controlled by the time delay of said optical signal coupled to said corresponding radiating element.

4. The device of claim 1 wherein said means for producing an optical signal is a variable wavelength laser.

5. The device of claim 1, wherein said antenna is steered by changing the wavelength of said optical signal.

8. The device of claim 1, wherein said means for dividing said modulated optical signal is an optical coupler.

9. The device of claim 1, wherein said means for dividing said modulated optical signal is an optical circulator.

10. The device of claim 1, wherein said means for dividing and means for time delaying is a chirped grating add/drop multiplexer.

11. The device of claim 1, where in said modulator is a Mach-Zehnder modulator.

2. A fiber optic based phased array antenna structure comprising:

means for dividing an optical signal into a plurality of component optical signals,

means for time delaying select components of said optical signal, said means for time delaying said select components, comprising chirped fiber gratings, said gratings disposed to allow passage of select components of said optical signal through select combinations of identical chirped fiber gratings to effect a distinct time shift on said corresponding component optical signal,

a plurality of radiating elements,

means for coupling each of said plurality of component optical signals with a corresponding radiating element.

6. The structure of claim 2, wherein said chirped fiber gratings are partially reflective, and wherein said means for coupling is disposed effective to cause light passing through each of said chirped fiber gratings to be input to a respective one of said plurality of radiating elements.

7. The structure of claim 2, wherein said chirped fiber gratings are partially reflective, and wherein said means for coupling is disposed effective to cause light reflected from each of said chirped fiber gratings to be input to a respective one of said plurality of radiating elements.

3. A fiber optic based phased array antenna comprising:

means for dividing an optical signal into a plurality of component optical signals,

means for time delaying select components of said optical signal, said means for time delaying said select components, comprising chirped fiber gratings, said gratings disposed to allow passage of select components of said optical signal through select combinations of identical chirped fiber gratings to effect a time shift on said corresponding component optical signal,

a plurality of radiating elements,

means for coupling each of said plurality of component optical signals with a correspond radiating element;

wherein each of said radiating elements produce an electromagnetic signal, the timing of said electromagnetic signal produced by each of said radiating elements being controlled by the time delay of said optical signal coupled to said corresponding radiating element.