Method and apparatus for correcting velocity-induced range estimate phase errors in a two-tone monopulse CW radar

• US 7,158,076 B2
• Filed: 10/01/2004
• Issued: 01/02/2007
• Est. Priority Date: 10/01/2004
• Status: Active Grant

• Current Assignee: BAE Systems Information and Electronic Systems Integration Incorporated (BAE Systems Plc)
• Original Assignee: BAE Systems Information and Electronic Systems Integration Incorporated (BAE Systems Plc)
• Inventors: Fiore, Paul D., Rundquist, Eric A.
• Primary Examiner(s): Tarcza, Thomas H.
• Assistant Examiner(s): Barker, Matthew M.
• Application Number:
  US10/956,837
• Publication Number:
  US 20060071847A1
• Time in Patent Office: 823 Days
• Field of Search: 342/129
• US Class Current: 342/129
• CPC Class Codes: G01S 13/38 wherein more than one modulation frequency is used
• CPC Class Codes: G01S 13/44 Monopulse radar, i.e. simultaneous lobing
• CPC Class Codes: G01S 13/584 adapted for simultaneous range and velocity measurements

Abstract

A method and apparatus is provided for correcting the phase difference estimate derived from a two-tone CW radar to correct velocity-induced range estimate phase errors by offsetting the phase difference estimate with a phase correction equal to either of the Doppler frequencies associated with returns from an object multiplied by the time interval between the samplings of the returned waveforms. The correction effectively eliminates the velocity-induced slippage between the phases of the retuned waveforms so that a comparison between the phases of the waveforms can be made to reduce or substantially eliminate range estimate bias.

Claims

1. A method for correcting velocity-induced range estimate errors from a two-tone CW radar which provides as an output the phase difference between Doppler-shifted returns from a moving object, comprising the steps of:

offsetting the phase difference with a correction equal to the Doppler-shifted frequency of one of the two-tone returns times the time interval between waveform samples; and

,

deriving range from the offset phase difference.

2. The method of claim 1, wherein the two tones are sequentially generated with a predetermined switching rate, and wherein the Doppler-shifted waveforms corresponding to the returns from the object are sequentially sampled with a predetermined time interval establishing the time interval between waveform samples.

3. The method of claim 2, wherein the length of a tone establishes a Nyquist switching rate.

4. The method of claim 3, wherein the velocity of the object exceeds 100 meters/second.

5. The method of claim 3, wherein the velocity of the object has an associated frequency that approaches the Nyquist switching rate.

6. The method of claim 5, wherein the velocity of the object has an associated frequency within 10 KHz of the Nyquist switching rate.

7. A method for improving the range accuracy for the range of a rapidly moving object derived from a two-tone CW radar from which sum and difference signals for the two frequencies associated with the two tones are available, comprising the steps of:

forming a first two-by-two matrix from the sum and difference signals for each of the two frequencies associated with the two tones;

factoring the first two-by-two matrix into a second matrix associated with range; and

,

determining range from the second two-by-two matrix by deriving the phase difference between Doppler-shifted waveforms corresponding to returns from the moving object and offsetting derived phase difference by a quantity equal to the Doppler-shifted frequency of one of the two-tone returns times the time interval between waveform samples.

8. The method of claim 7, wherein the first two-by-two matrix is a Rank One matrix in the absence of noise.

9. The method of claim 7, wherein the factoring step includes the step of performing a singular value decomposition.

10. The method of claim 7, wherein the range determining step includes the step of determining the phase between the complex numbers in the first column of the second matrix.

11. The method of claim 7, wherein the two tones are sequentially generated with a predetermined switching rate, and wherein the Doppler-shifted waveforms corresponding to the returns from the object are sequentially sampled with a predetermined time interval establishing the time interval between waveform samples.

12. The method of claim 11, wherein the length of a tone is 5 microseconds, thus to establish a Nyquist switching rate of 50 KHz.

13. The method of claim 12, wherein the velocity of the object exceeds 100 meters/second.

14. The method of claim 12, wherein the velocity of the object has an associated frequency that approaches the Nyquist switching rate.

15. The method of claim 14, wherein the velocity of the object has an associated frequency within 10 KHz of the Nyquist switching rate.

16. In a system for countermeasuring a rocket-propelled grenade using a multiple-barrel gun that projects a pattern of shot towards an incoming rocket-propelled grenade, a method for improving the aiming and firing accuracy of the gun, comprising the step of:

using a two-tone monopulse CW radar that develops sum and difference signals for deriving the range of said rocket-propelled grenade relative to the radar;

the step of deriving the range of the incoming rocket-propelled grenade including the steps of;

forming a first two-by-two matrix from the sum and difference signals for each of the two frequencies associated with the two tones;

factoring the first two-by-two matrix into a second matrix associated with range;

determining range from the second two-by-two matrix by deriving the phase difference between Doppler-shifted waveforms corresponding to returns from the moving object and offsetting derived phase difference by a quantity equal to the Doppler-shifted frequency of one of the two-tone returns times the time interval between waveform samples; and

,

aiming and firing the gun based on the range measurement from the radar.

17. The method of claim 16, wherein the first two-by-two matrix is a Rank One matrix in the absence of noise.

18. The method of claim 16, wherein the factoring step includes the step of performing a singular value decomposition.

19. The method of claim 16, wherein the range determining step includes the step of determining the phase between the complex numbers in the first column of the second matrix.

20. A system for improving the range estimate of a target moving relative to a two-tone CW radar from which sum and difference signals for the two frequencies associated with the two tones are available, in which the two tones are sequentially generated and in which the Doppler-shifted waveforms corresponding to the two-tone returns from said target are sequentially sampled, comprising:

a down converter for down-converting, low pass filtering and sampling said sum and difference signals;

a demultiplexer for providing time domain data streams corresponding to the down-converted, low pass filtered and sampled sum and difference signals;

a module coupled to said demultiplexer for performing a Fast Fourier Transform on said time-domain data stream to produce associated frequency domain data streams in the form of individual frequency bins;

a calculator for squaring the magnitude of the individual bins to produce magnitude-squared values;

an accumulator for accumulating said magnitude-squared values;

a peak search detector for determining from the accumulated magnitude-squared values which of said frequency bins has the highest peak, thus to determine which of said frequency bins contains said target;

a process or for generating a first two-by-two matrix from the sum and difference values associated with the bin that is determined to contain said target;

a unit for performing a singular value decomposition of said first two-by-two matrix so as to factor said first matrix into a second and third matrix respectively related to range and angle of arrival;

a phase detector for detecting the phase difference between the complex numbers in the first column of said second matrix, thus to derive range; and

,

a phase correction module for offsetting said phase difference by a quantity equaling the Doppler-shifted frequency of one of the two-tone returns from said target multiplied by the time interval between successive samplings of the waveforms associated with said two-tone returns.