Transponder data processing methods and systems

• US 6,577,266 B1
• Filed: 10/15/2001
• Issued: 06/10/2003
• Est. Priority Date: 10/15/2001
• Status: Active Grant

• Current Assignee: National Technology & Engineering Solutions Of Sandia LLC (Honeywell International Inc.)
• Original Assignee: Sandia Corporation (Martin Marietta Corporation)
• Inventors: Axline, Robert M.
• Primary Examiner(s): Sotomayor, John B.
• Application Number:
  US09/977,841
• Time in Patent Office: 603 Days
• Field of Search: 342/42, 342/44, 342/45, 342/50, 342/51, 342/60, 342/82, 342/83, 342/84, 342/159, 342/162, 342/195
• US Class Current: 342/42
• CPC Class Codes: G01S 13/765 with exchange of information between interrogator and responder
• CPC Class Codes: G01S 13/9029 specially adapted for moving target detection within a single SAR image or within multiple SAR images taken at the same time

Abstract

This invention is a radar/tag system where pulses from a radar cause a tag (or transponder) to respond to the radar. The radar, along with its conventional pulse transmissions, sends a reference signal to the tag. The tag recovers the reference signal and uses it to shift the center frequency of the received radar pulse to a different frequency. This shift causes the frequencies of the tag response pulses to be disjoint from those of the transmit pulse. In this way, radar clutter can be eliminated from the tag responses. The radar predicts, to within a small Doppler offset, the center frequency of tag response pulses. The radar can create synthetic-aperture-radar-like images and moving-target-indicator-radar-like maps containing the signature of the tag against a background of thermal noise and greatly attenuated radar clutter. The radar can geolocate the tag precisely and accurately (to within better than one meter of error). The tag can encode status and environmental data onto its response pulses, and the radar can receive and decode this information.

Claims

1. A method for communicating between radars and tag devices, said method comprising the steps of:

receiving at a tag pulse radar signals transmitted from a radar, said radar signals comprising a pulsed waveform transmitted at first frequency f_t and having a bandwidth extending around f_t, wherein frequencies outside the bandwidth are defined as out-of-band;

processing said pulse radar signals at the tag to generate a stable reference frequency, said reference frequency being derived only from said radar signals;

shifting said received radar signal by a function of said reference frequency to form an out-of-band tag signal; and

transmitting said tag signal to said radar.

2. The method of claim 1 further comprising:

receiving reflected pulse radar signals at said radar and processing said signals to generate a radar image;

receiving said tag signal at said radar; and

said radar using said received tag signal to locate said tag within said radar image.

3. The method of claim 1 wherein said out-of-band frequency is an integer multiple of said reference frequency.

4. The method of claim 1 wherein said transmitted pulse radar signal further comprises two out-of-band downlink tones and said reference frequency is the frequency difference between said tones.

5. A method for locating and communicating with at least one tag, said method comprising the steps of:

transmitting a radar signal from a radar to a general geographic location containing at least one tag, said radar signal comprising a radar pulse centered at a first frequency and two sinusoidal tones; and

receiving, at said radar, tag data retransmitted from at least one tag at a second frequency that is out-of-band with respect to said radar pulse, wherein the second frequency is a predetermined function of the frequency difference between the two sinusoidal tones.

6. The method of claim 5 further comprising the steps of:

receiving said transmitted radar signal at a tag;

processing at said tag said radar signal to determine the frequency difference between the two sinusoidal tones in said pulsed radar signal;

determining at said tag said second frequency; and

transmitting tag data to said radar at said second frequency.

7. The method of claim 6 wherein said second frequency differs from said first frequency by a multiple of said frequency difference.

8. The method of claim 6 wherein said tag data comprises at least one of geolocation sequences and environmental information.

9. The method of claim 8 wherein said tag data comprises environmental information.

10. The method of claim 7 wherein said tag data further comprises geolocation sequences.

11. The method of claim 5 further comprising the step of:

processing said tag data to determine environmental information and/or tag internal data associated with said tag'"'"'s geolocation.

12. A system for communicating between radar and tag devices, said system comprising:

a tag receiver receding radar pulse signals comprising a radar pulse centered at a first frequency and two out-of-band sinusoidal tones, wherein frequencies not in the frequency range of said radar pulse are out-of-band;

a tag processor processing said radar pulse signals to determine an out-of-band second frequency that differs from said first frequency by a predetermined function of the frequency difference between the two sinusoidal tones; and

a tag transmitter for transmitting data from said tag at said out-of-band second frequency;

wherein said second frequency is not dependent upon a tag local oscillator.

13. The system of claim 12 further comprising:

a radar transmitter for transmitting said radar signal at said first frequency; and

a radar receiver for receiving said data transmitted at an out-of-band second frequency from said tag.

14. The system of claim 12 wherein said tag processor comprises a mixer to extract a difference frequency from said two sinusoidal tones in the radar pulse;

and a frequency multiplier to multiply the difference frequency by a predetermined multiple.

15. The system of claim 14 wherein said radar pulse signals comprise a chirp radar pulse having a bandwidth extending about said first frequency, and wherein the second frequency is out-of-band relate to said radar pulse.

16. The system of claim 14 further comprising:

a synthetic aperture radar transmitter for transmitting said pulse signals, wherein said radar pulse is a chirped synthetic aperture radar signal at said first frequency; and

a synthetic aperture radar receiver for receiving reflected target information at said first frequency and said data from said tag at said second frequency, said receiver further comprising means for forming a synthetic aperture radar image from said information, and means for using said received data to accurately locate the position of said tag on said image.

17. A program product for communicating between radars and tag devices, wherein said program product resides in computer memory in a computer, said program product comprising:

a module residing in computer memory for receiving radar pulse signals from a radar at a tag;

a module residing in computer memory for processing said radar pulse signals to determine an out-of-band frequency from parameters of said radar pulse for transmission of tag data back to said radar from said tag; and

a module residing in computer memory for transmitting tag data to said radar by said tag at said out-of-band frequency.

18. The program product of claim 17 further comprising:

a module residing in computer memory for receiving tag data transmitted at said out-of-band frequency at said radar.

19. The program product of claim 17 wherein said out-of-band frequency is determined by extracting a reference frequency from said radar pulse and rendering an out-of-band frequency known by said radar based on said reference frequency.

20. A tag comprising:

a receiver for receiving radar pulses transmitted from at least one radar, said pulses being received at a first frequency;

a tone recovery module for extracting a reference frequency from the transmitted radar pulses;

a frequency translation module for generating a second frequency that is the sum of the received first frequency and a multiple of said reference frequency; and

a transmitter for transmitting said received radar pulses from the tag to at least one radar at said second frequency, wherein no local oscillator at said tag is used in the generation of said second frequency.