Electro optical scanning phased array antenna for pulsed operation

• US 20090002236A1
• Filed: 06/26/2007
• Published: 01/01/2009
• Est. Priority Date: 06/26/2007
• Status: Active Grant

• 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 Agriculture
• Inventors: Zhou, Weimin
• Granted Patent: US 8,779,977 B2
• Time in Patent Office: Days
• US Class Current: 342/375
• CPC Class Codes: H01Q 1/28 Adaptation for use in or on aircraft, missiles, satellites, or balloons
• CPC Class Codes: H01Q 3/2676 Optically controlled phased array

Abstract

An electro optical scanning phased array antenna having a laser which generates a pulsed output. A microwave source has an output which amplitude modulates the optical output from the laser through an optical modulator. An optical loop circuit has an input connected to an output from the optical modulator and a variable time delay element. The optical loop circuit generates a plurality of modulated optical pulses at equidistantly spaced time intervals from each other at an output from the loop circuit. These time intervals vary as a function of the variable time delay element and a control circuit controls the time delay attributable to the variable time delay element. An antenna array includes end elements while a circuit converts the optical output pulses from the optical loop circuit to radio frequency signals electrically connected to the elements of the antenna array.

Claims

1. An electro optical scanning antenna comprising:

a laser which generates an optical output pulse,

an RF microwave source having an output which amplitude modulates the optical output pulse from said laser via an optical modulator,

an optical loop circuit having an input connected to an output from said optical modulator and a variable time delay element, wherein said optical loop circuit generates a plurality of modulated output pulses at equidistantly spaced time intervals from each other at an output from said loop circuit, said time intervals varying as a function of the delay attributable to said variable time delay element,

a control circuit which controls the time delay of said variable time delay element,

an antenna array having N elements,

means for converting the optical output pulses from said optical loop circuit to radio frequency signals electrically connected to said elements of said antenna array.

2. The invention as defined in claim 1 wherein said laser comprises a variable wavelength tunable laser, wherein said variable time delay element comprises a wavelength-dependant time delay element and wherein said control circuit controls the wavelength of said laser.

3. The invention as defined in claim 1 wherein said laser comprises a fixed wavelength laser, wherein said variable time delay element comprises an electro-optical waveguide device with an index which varies as a function of electrical bias applied to said waveguide device and wherein said control circuit controls the bias applied to said electro-optical waveguide device.

4. The invention as defined in claim 1 wherein said converting means comprises a plurality of photodetectors, each photodetector having a radio frequency output connected with one of said elements, at least N−

1 optical switches, each optical switch having one input and a first and second output, said switch input and said first output of each switch being connected in series with said loop output, each switch second output being optically connected as an input signal to a selected photodetector associated with each element.

5. The invention as defined in claim 2 wherein said wavelength-dependent time delay element comprises a photonic bandgap waveguide.

6. The invention as defined in claim 2 wherein said wavelength-dependent time delay element comprises an optical fiber grating used in transmission mode.

7. The invention as defined in claim 1 wherein said optical switches are connected in series by an optical fiber having a length selected to introduce a time delay substantially equal to the time delay of said optical loop at a preselected optical wavelength.

8. The invention as defined in claim 7 wherein each optical output pulse from said loop reaches each photodetector at substantially the same time at said preselected initial tuning position.

9. The invention as defined in claim 1 wherein said loop circuit comprises an optical amplifier.

10. The invention as defined in claim 9 wherein said loop circuit further comprises a 2×

2 optical coupler, said optical modulator output being connected on one coupler input, said variable time delay element being connected between the other input and one output of said coupler, and the other coupler output being connected to said converting means.

11. The invention as defined in claim 10 wherein said loop circuit comprises a fixed time delay element connected in series with said variable time delay element.

12. The invention as defined in claim 4 and comprising a receiving configuration with a radio frequency mixer associated with each element and having two inputs and one output, each said element being connected to one input of its associated mixer and the output of each photodetector associated with each said element being connected to the other mixer input, radio frequency processing means being connected to each said mixer output.

13. The invention as defined in claim 12 and comprising a plurality of radio frequency amplifiers, one radio frequency amplifier being connected in series between each photodetector and its associated mixer input, and between each element and its associated mixer input.

14. The invention as defined in claim 1 wherein said converting means comprises a photodetector having an input connected to said loop circuit output and a radio frequency output,

at least N−

1 radio frequency switches, each radio frequency switch having an input and a first and a second outputs, said radio frequency switch input and said first output of each radio frequency switch being connected in series through an radio frequency electrical cable delay, each radio frequency switch second output being connected to its associated element.

15. The invention as defined in claim 14 and comprising a radio frequency amplifier connected in series with each radio frequency switch output.

16. The invention as defined in claim 2 and comprising:

a second variable wavelength tunable laser having a frequency different than said first mentioned laser,

a second control circuit which controls the wavelength of said second laser,

a second microwave source having an output which amplitude modulates an optical output from said second laser via an optical modulator,

an optical combiner which combines the outputs from both said lasers into a combined output signal, said combined output signal being coupled as an input signal to said optical loop circuit.

17. An electro optical scanning antenna comprising:

a laser which generates an optical output pulse,

a control circuit which controls the wavelength of said laser,

a microwave source having an output which amplitude modulates an optical output from said laser via an optical modulator,

an optical loop circuit having an input connected to an output from said optical modulator and a variable time delay element, wherein said optical loop circuit generates a plurality of modulated optical output pulses at equidistantly spaced time intervals from each other at an output from said loop circuit, said time intervals varying as a function of the delay attributable to said variable time delay element,

a control circuit which controls the time delay of said variable time delay element,

an antenna array having N elements,

means for synchronizing received signals on said elements with said output from said loop circuit.

18. The invention as defined in claim 17 wherein said laser comprises a variable wavelength tunable laser, wherein said variable time delay element comprises a wavelength-dependant time delay element and wherein said control circuit controls the wavelength of said laser.

19. The invention as defined in claim 17 wherein said laser comprises a fixed wavelength laser, wherein said variable time delay element comprises an electro-optical waveguide device with an index which varies as a function of electrical bias applied to said waveguide device and wherein said control circuit controls the bias applied to said electro-optical waveguide device.

20. The invention as defined in claim 17 wherein said synchronizing means comprises an optical modulator associated with each element so that the output from each element modulates its associated optical modulator, said modulators being optically connected in series with each other through fixed time delay elements, a fixed frequency laser connected as an input signal to one end of said series of said optical modulators, a first photodetector having an input connected to an end of said series of said optical modulators opposite from said laser, a second photodetector having an input connected to said loop circuit output, and an output from each photodetector connected as input signals to a radio frequency mixer.

21. The invention as defined in claim 20 and comprising a radio frequency amplifier connected in series between each element and its associated optical modulator.

22. The invention as defined in claim 17 wherein said synchronizing means comprises a radio frequency mixer having two inputs, a photodetector connected in series between said loop circuit output and one input of said radio frequency mixer, an output signal from said elements being combined and connected in series by radio frequency time delay cables, each cable having substantially the same time delay, said combined element signals being connected as an input signal to the other input of said radio frequency mixer.

23. The invention as defined in claim 22 and comprising a radio frequency amplifier connected in series with at least one radio frequency time delay cable.