Antenna calibration method and system

• US 7,408,507 B1
• Filed: 03/14/2006
• Issued: 08/05/2008
• Est. Priority Date: 03/15/2005
• 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: Choe, Joon Y, Paek, Eung Gi, Parent, Mark
• Primary Examiner(s): Tarcza; Thomas H.
• Assistant Examiner(s): Liu; Harry
• Application Number:
  US11/376,633
• Time in Patent Office: 875 Days
• Field of Search: 342/22, 342/54, 342/78, 342/167, 342/172, 342/174, 342/360, 342/368, 342/375, 342/398
• US Class Current: 342/368
• CPC Class Codes: H01Q 1/405 Radome integrated radiating elements
• CPC Class Codes: H01Q 15/0053 Selective devices used as spatial filter or angular sidelobe filter
• CPC Class Codes: H01Q 21/061 Two dimensional planar arrays
• CPC Class Codes: H01Q 3/267 Phased-array testing or checking devices
• CPC Class Codes: H01Q 3/2676 Optically controlled phased array
• CPC Class Codes: H01Q 7/00 Loop antennas with a substantially uniform current distribution around the loop and having a directional radiation pattern in a plane perpendicular to the plane of the loop
• CPC Class Codes: H01Q 9/26 with folded element or elements, the folded parts being spaced apart a small fraction of operating wavelength resonant loop antennas H01Q7/00

Abstract

A phased array antenna system includes an RF front end, a radome, and an optical calibrator embedded in the radome for enabling in-situ calibration of the RF front end. The optical calibrator employs an optical timing signal generator (OTSG), a Variable Optical Amplitude and Delay Generator array (VOADGA) for receiving the modulated optical output signal and generating a plurality of VOADGA timing signals, and an optical timing signal distributor (OTSD). The in-situ optical calibrator allows for reduced calibration time and makes it feasible to perform calibration whenever necessary.

Claims

1. A method of calibrating a phased array antenna housed within a radome, comprising:

a) providing an optical timing signal generator (OTSG) having a DFB laser source for generating an optical calibration signal, a modulator for modulating the light calibration signal and generating a modulated optical output signal, and a Variable Optical Amplitude and Delay Generator array (VOADGA) for receiving the modulated optical output signal and generating a plurality of VOADGA timing signals, and an optical timing signal distributor (OTSD) housed within the radome for receiving the plurality of VOADGA timing signals, the OTSD having a matrix-addressable PLC having N horizontal waveguides and N vertical waveguides for receiving the VOADGA timing signals, said wave guides having a plurality of intersections, each intersection having a photodiode positioned thereon for receiving a portion of the VOADGA timing signals and for generating a proportional electrical output signal for subsequent processing and calibrating of the phased array antenna;

b) optimizing RF delays to compensate for PLC delays, line-by-line;

c) aligning VOADGA delays so that incoming input signals have the same phase at the entrance of the matrix;

d) adding linear chirp delays to VOADGA to steer beam directions;

e) optimizing RF delays to match the additional VOADGA delays and record the RF delay values to form a look-up-table (LUT);

f) repeating steps d)-e) for all the beam positions along the azimuth and elevation directions;

g) adding additional linear chirp delays to the VOADGA to scan through the beam pattern and to estimate sidelobes; and

h) then tapering RF amplitudes in the RF front-end of the phased array antenna to minimize the sidelobe level.

2. A method as in claim 1, wherein each intersection of the matrix-addressable PLC includes an upper-cladding layer that is etched so as to permit evanescent beam coupling in a selected direction.

3. A method as in claim 1, wherein each waveguide is single mode.

4. A method as in claim 1, wherein the step of optimizing RF delays line-by-line commences with obtaining an expected target peak.

5. A method as in claim 1, wherein each photodiode is a photovoltaic mode photodiode.

6. A method as in claim 5, wherein each photodiode is a PIN InGaAs photodiode.

7. A method as in claim 5, wherein each photodiode is selected such that mutual time delay differences are less than a target design timing resolution.

8. A method as in claim 1, wherein the PLC has a timing precision of up to about 0.005 ps.