Optical monopulse chirp processor

• US 5,546,089 A
• Filed: 08/10/1995
• Issued: 08/13/1996
• Est. Priority Date: 08/10/1995
• Status: Expired due to Fees

• Current Assignee: United States Air Force (Government of the United States of America)
• Original Assignee: United States Of America As Represented By The Secretary Of The Air Force
• Inventors: Talbot, Pierre J.
• Primary Examiner(s): Sotomayor, John B.
• Application Number:
  US08/513,369
• Time in Patent Office: 369 Days
• Field of Search: 342/159, 342/162, 342/52, 342/54, 342/93, 342/192
• US Class Current: 342/159
• CPC Class Codes: G01S 13/282 using a frequency modulated carrier wave G01S13/286 takes precedence
• CPC Class Codes: G01S 13/44 Monopulse radar, i.e. simultaneous lobing
• CPC Class Codes: G01S 13/5244 Adaptive clutter cancellation specially adapted for airborne MTI, G01S13/5242
• CPC Class Codes: G01S 13/5246 post processors for coherent MTI discriminators, e.g. residue cancellers, CFAR after Doppler filters
• CPC Class Codes: G01S 7/2927 by deriving and controlling a threshold value

Abstract

An optical chirp processor for the collection and processing clutter samples is presented that allows the simultaneous estimation of both the clutter mean and variance. The estimated clutter mean and variance allow the actual calculation of both clutter model parameters using a power spectrum analyzer, and a CFAR special purpose processor unit. The power spectrum analyzer is composed of: a spatial frequency demultiplexor, and a four element photodetector array. The special purpose processor is composed of: an A/D converter, a square root calculator, an averaging calculator, a combiner unit, a parameter memory unit, and a threshold calculator unit. The components of the CFAR processor may be implemented in a conventional CFAR processor (when modified by the teachings of the present invention) or in individual electronics components.

Claims

1. An optical processor system for use with a phased array radar system for calculating a detection threshold using radar echo return signals which contain clutter components from at least four antenna elements of said phased array radar system, wherein said optical processor system comprises:

a power spectrum analyzer unit which receives and processes the radar echo return signals of said antenna elements of said phased array radar system to output thereby a set of transverse electric signals that represent a square of the clutter components of the radar echo return signals; and

a means for digitally calculating a detection threshold from the set of transverse electric signals produced by the power spectrum analyzer.

2. An optical processor system, as defined in claim 1, wherein said power spectrum analyzer unit comprises:

a spatial frequency multiplexor unit which receives and processes the radar echo return signals of said antenna elements to output thereby a set of optical beams which each represent the square of the clutter component received by a single antenna element; and

a set of optical photodetectors in a sensor array which photoelectrically convert said set of optical beams into said set of transverse electric signals for said digitally calculating means.

3. An optical processor system, as defined in claim 1, wherein said means for digitally calculating said detection threshold comprises:

a means for converting said set of transverse electric signals from said power spectrum analyzer unit into discrete sets of digital data streams;

a means for deriving a set of digital clutter measurement signals from said discrete set of digital data streams from said converting means;

a means for combining said set of digital clutter measurement signals from said deriving means into a combined clutter measurement signal;

a means for producing an average clutter measurement signal from the combined clutter measurement signal; and

a CFAR digital processor system which calculates said detection threshold from said average clutter measurement signal from said producing means.

4. An optical processor system, as defined in claim 2, wherein said means for digitally calculating said detection threshold comprises:

a means for converting said set of transverse electric signals from said power spectrum analyzer unit into discrete sets of digital data streams;

a means for combining said set of digital clutter measurement signals from said deriving means into a combined clutter measurement signal;

a means for producing an average clutter measurement signal from the combined clutter measurement signal; and

a CFAR digital processor system which calculates said detection threshold from said average clutter measurement signal from said producing means.

5. An optical processor system, as defined in claim 3, wherein said CFAR digital processor system comprises:

a memory means which is capable of producing an output signal by storing and outputting said average clutter measurement signal from said producing means along with a set of detection threshold formulas for calculating said detection threshold with Raleigh distribution and with Weibull distribution; and

a microprocessor element which calculates and outputs the detection threshold using the output signal of said memory means.

6. An optical processor system, as defined in claim 4, wherein said CFAR digital processor system comprises:

a memory means which is capable of producing an output signal by storing and outputting said average clutter measurement signal from said producing means along with a set of detection threshold formulas for calculating said detection threshold with Raleigh distribution and with Weibull distribution; and

a microprocessor element which calculates and outputs the detection threshold using the output signal of said memory means.

7. An optical processor system for use with a phased array radar system for calculating a detection threshold using radar echo return signals which contain clutter components from at least four antenna elements of said phased array radar system, wherein said optical processor system comprises:

a heterodyne spectrum analyzer unit which receives and processes the radar echo return signals of said antenna elements of said phased array radar system to output thereby a set of transverse electric signals that represent a magnitude of the clutter components of the radar echo return signals; and

a means for digitally calculating a detection threshold from the set of transverse electric signals produced by the heterodyne spectrum analyzer.

8. An optical processor system, as defined in claim 7, wherein said heterodyne spectrum analyzer unit comprises:

a spatial frequency multiplexor unit which receives and processes the radar echo return signals of said antenna elements to output thereby a set of optical beams which each represent the magnitude of the clutter component received by a single antenna element; and

a set of optical photodetectors in a sensor array which photoelectrically convert said set of optical beams into said set of transverse electric signals for said digitally calculating means.

9. An optical processor system, as defined in claim 7, wherein said means for digitally calculating said detection threshold comprises:

a means for converting said set of transverse electric signals from said heterodyne spectrum analyzer unit into discrete sets of digital data streams;

a means for combining said discrete set of digital data streams clutter measurement signals from said converting means into a combined clutter measurement signal;

a means for producing an average clutter measurement signal from the combined clutter measurement signal; and

a CFAR digital processor system which calculates said detection threshold from said average clutter measurement signal from said producing means.

10. An optical processor system, as defined in claim 8, wherein said means for digitally calculating said detection threshold comprises:

a means for converting said set of transverse electric signals from said heterodyne spectrum analyzer unit into discrete sets of digital data streams;

a means for combining said discrete set of digital data stream clutter measurement signals from said converting means into a combined clutter measurement signal;

a means for producing an average clutter measurement signal from the combined clutter measurement signal; and

a CFAR digital processor system which calculates said detection threshold from said average clutter measurement signal from said producing means.

11. An optical processor system, as defined in claim 9, wherein said CFAR digital processor system comprises:

a memory means which is capable of producing an output signal by storing and outputting said average clutter measurement signal from said producing means along with a set of detection threshold formulas for calculating said detection threshold with Raleigh distribution and with Weibull distribution; and

a microprocessor element which calculates and outputs the detection threshold using the output signal of said memory means.

12. An optical processor system, as defined in claim 10, wherein said CFAR digital processor system comprises:

a memory means which is capable of producing an output signal by storing and outputting said average clutter measurement signal from said producing means along with a set of detection threshold formulas for calculating said detection threshold with Raleigh distribution and with Weibull distribution; and

a microprocessor element which calculates and outputs the detection threshold using the output signal of said memory means.