Method and apparatus for range correction in a radar system

• US 6,317,076 B1
• Filed: 09/12/2000
• Issued: 11/13/2001
• Est. Priority Date: 07/23/1999
• Status: Expired due to Fees

• Current Assignee: Bendix Commercial Vehicle Systems LLC (Estate of Heinz Hermann Thiele)
• Original Assignee: Eaton Vorad Technologies, LLC
• Inventors: Ameen, Yashwant K., Ryan, Patrick Anthony, Gingell, Thomas W.
• Primary Examiner(s): Sotomayor, John B.
• Application Number:
  US09/660,510
• Time in Patent Office: 427 Days
• Field of Search: 342/70, 342/71, 342/72, 342/114, 342/115, 342/160, 342/162, 342/196, 342/173, 342/174
• US Class Current: 342/174
• CPC Class Codes: G01S 13/931 of land vehicles
• CPC Class Codes: G01S 2013/93271 in the front of the vehicles
• CPC Class Codes: G01S 2013/93275 in the bumper area
• CPC Class Codes: G01S 2013/9329 cooperating with reflectors or transponders
• CPC Class Codes: G01S 7/4021 of receivers
• CPC Class Codes: G01S 7/403 in azimuth, i.e. in the horizontal plane
• CPC Class Codes: G01S 7/4091 during normal radar operation

Abstract

A method and apparatus for calibrating range in a radar system. Due mainly to temperature changes in a radar system which cause frequency deviation error, range errors can be introduced into the radar system, thus adversely affecting the determination of the position of targets relative to the host platform. These range errors can be corrected by detecting and accurately estimating the frequency deviation error of a radar system. The present invention improves target position determination performance in a radar system by reducing errors introduced by the frequency deviation error. The present invention relies upon the observation that the Doppler range rate is largely unaffected by frequency deviation error, and thus, is approximately equal to the actual range rate. In accordance with a first range calibration technique of the present invention, the radar system measures the range, Doppler range rate, and azimuth angle of a target during at least two successive time instances. If the measured data is qualified the method corrects the range using a frequency deviation correction factor, K. A second calibration technique of the present invention relies upon both the observation that the Doppler range rate is largely unaffected by frequency deviations and the observation that certain target tracks provide more reliable data than other target tracks. Thus, tracks with more reliable data are given more weight in calibrating the range. The second calibration technique qualifies data, updates a frequency deviation correction factor, and corrects the range using the frequency deviation correction factor. The voltage bias implementation of the present method can be used with either the first or second calibration technique to calibrate the range. In the voltage bias implementation, the range is corrected by adjusting the voltage of the radar system'"'"'s RF (radio frequency) source.

Claims

1. A method of calibrating a range measurement in a radar system comprising an antenna and a computer, comprising the steps of:

a) selecting a calibration target for use in calibrating the range measurement;

b) obtaining an initial measurement of a target range and a Doppler range rate at a first time instance;

c) obtaining subsequent measurements of the target range and the Doppler range rate at successive time instances subsequent to the first time instance;

d) qualifying the calibration target;

e) calculating a frequency deviation correction factor caused by a frequency deviation using the initial and subsequent target range and Doppler range rate measurements obtained at sub-steps (b) and (c), and smoothing the subsequent target range measurements to obtain the frequency deviation correction factor; and

f) calibrating the range to compensate for the frequency deviation.

2. The method of claim 1, wherein the calculating step (e) uses a least-squared smoothing equation.

3. The method of claim 1, wherein the qualifying step (d) includes the sub-steps of:

i) qualifying an initial set of measurements;

ii) qualifying an intermediate set of measurements; and

iii) qualifying a final set of measurements.

4. The method of claim 3, wherein the qualifying sub-steps (i) and (iii) comprise determining whether a target range is within a pre-determined set of ranges.

5. The method of claim 4, wherein the predetermined set of ranges is between 9 meters and 90 meters.

6. The method of claim 3, wherein the qualifying sub-steps (i) and (iii) comprise determining whether a target rate is within a pre-determined set of rates.

7. The method of claim 6, wherein the predetermined set of rates for the qualifying sub-step (i) is greater than or equal to approximately 2 meters/second.

8. The method of claim 6, wherein the predetermined set of rates for the qualifying sub-step (iii) is greater than or equal to approximately 1.5 meters/second.

9. The method of claim 3, wherein the qualifying sub-steps (i) and (iii) comprise determining whether a signal magnitude is within a pre-determined set of signal magnitudes.

10. The method of claim 9, wherein the predetermined set of signal magnitudes is greater than or equal to approximately 100 dB.

11. The method of claim 3, wherein the qualifying sub-steps (i) and (iii) comprise determining whether a target turn radius is within a pre-determined set of turn radii.

12. The method of claim 3, wherein the qualifying sub-step (ii) comprises determining whether a data dropout rate exceeds a pre-determined data dropout rate.

13. The method of claim 1, wherein the calculating step (e) comprises calculating a frequency deviation correction factor, K, according to the following equation:

14. The method of claim 1, wherein the calibrating step (f) comprises multiplying a measured range by the frequency deviation correction factor.

15. The method of claim 1, wherein the calibrating step (f) comprises biasing an RF source of the radar system to compensate for the frequency deviation correction factor.

16. The method of claim 1, wherein the calibration target comprises a plurality of target tracks, and wherein each target track corresponds to a radar target.

17. The method of claim 16, wherein the calculating step (e) comprises the sub-steps of:

i) calculating a frequency deviation error measurement; and

ii) calculating the frequency deviation correction factor based on the frequency deviation error measurement.

18. The method of claim 17, wherein the frequency deviation error measurement, FDEM(k,n), is calculated according to the following equation:

$\mathrm{FDEM}<br><br>\left(k,n\right)=\frac{\left(R<br><br>\left(k\right)-R<br><br>\left(k-1\right)\right)}{\left(0.5<br><br>V<br><br>\left(k\right)<br><br><br><br>t+0.5<br><br>V<br><br>\left(k-1\right)<br><br><br><br>t\right)}.$

19. The method of claim 17, wherein the sub-step (i) of calculating the frequency deviation error measurement, ADEM(n), is obtained from a weighted average value for a plurality of target tracks.

20. The method of claim 19, wherein ADEM(n) is calculated according to the following equation:

21. The method of claim 17, wherein the sub-step (ii) comprises calculating a frequency deviation correction factor according to the following equation:

22. A method of calibrating a range measurement in a radar system comprising an antenna and a computing device, comprising the steps of:

a) selecting a calibration target for use in calibrating a range measurement;

b) obtaining a first measurement of a target range and a Doppler range rate at a first time instance;

c) obtaining a second measurement of the target range and the Doppler range rate at a second time instance;

d) qualifying the first measurement and the second measurement;

e) discarding the first measurement and the second measurement and returning to step (a) if the first measurement or the second measurement is determined not qualified;

f) smoothing a plurality of target ranges if the first measurement and the second measurement are determined qualified;

g) obtaining a subsequent measurement of the target range and the Doppler range rate at a successive time instance subsequent to the second time instance;

h) qualifying the subsequent measurement obtained in step (g);

i) returning to step (f) if the subsequent measurement is determined not qualified;

j) qualifying a recent measurements if the subsequent measurement is qualified;

k) discarding the recent measurements and returning to step (a) if the recent measurements are not qualified;

l) calculating a frequency deviation correction factor caused by a frequency deviation; and

m) calibrating a range measurement for the radar system in compensation for the frequency deviation calculated in step (l).

23. A method of calibrating a range measurement in a radar system comprising an antenna and a computing device, wherein the computing device is capable of tracking a plurality of targets, and wherein each of the plurality of targets has a corresponding track and track set, and wherein a track set comprises data corresponding to a target, the method comprising the steps of:

a) obtaining a track set update corresponding to a target;

b) qualifying the track set update obtained in step (a);

c) calculating a gain for the track set obtained in step (a);

d) calculating a frequency deviation correction factor; and

e) calibrating the radar system responsive to the frequency deviation correction factor calculated in step (d), wherein the calibration compensates for any frequency deviation.