FM-CW radar system for measuring distance to and relative speed of a target

• US 6,317,073 B1
• Filed: 09/07/1999
• Issued: 11/13/2001
• Est. Priority Date: 09/07/1998
• Status: Expired due to Term

• Current Assignee: DENSO Corporation
• Original Assignee: DENSO Corporation
• Inventors: Kumon, Hiroaki, Tamatsu, Yukimasa
• Primary Examiner(s): Lobo, Ian J.
• Application Number:
  US09/390,316
• Time in Patent Office: 798 Days
• Field of Search: 342/70, 342/109, 342/114, 342/128
• US Class Current: 342/70
• CPC Class Codes: G01S 13/345 using triangular modulation
• CPC Class Codes: G01S 13/44 Monopulse radar, i.e. simultaneous lobing
• CPC Class Codes: G01S 13/931 of land vehicles
• CPC Class Codes: G01S 2013/932 using own vehicle data, e.g. ground speed, steering wheel direction
• CPC Class Codes: G01S 2013/9322 using additional data, e.g. driver condition, road state or weather data
• CPC Class Codes: G01S 2013/9325 for inter-vehicle distance regulation, e.g. navigating in platoons
• CPC Class Codes: G01S 2013/93271 in the front of the vehicles
• CPC Class Codes: G01S 7/352 Receivers
• CPC Class Codes: G01S 7/356 involving particularities of FFT processing
• CPC Class Codes: G01S 7/4021 of receivers

Abstract

An FM-CW radar is provided which may be employed in anti-collision systems or cruise control systems installed in moving objects such as automotive vehicles. The radar produces a first spectrum using a portion of a beat signal in a frequency rising range wherein the frequency of the radar wave increases and a second spectrum using a portion of the beat signal in a frequency falling range wherein the frequency of the radar wave decreases and moves the second spectrum by frequency shifts which are determined as a function of the speed of a radar-mounted vehicle and corrected for compensating various errors involved in measuring the speed of the vehicle to form spectrum groups each consisting of the frequency components moved by one of the corrected frequency shifts and frequency components in the other of the first and second spectra. The radar selects an optimum one of the spectrum groups for use in determining target data.

Claims

1. An FM-CW radar apparatus for a vehicle comprising:

a radar wave transmitter transmitting a radar wave having a frequency modulated so as to increase at a given rate and decrease at a given rate cyclically;

a radar wave receiver receiving a return of the radar wave from a target object present in a radar detection zone to mix the return of the radar wave with the radar wave transmitted from said radar wave transmitter to produce a beat signal;

a spectrum producing circuit producing a first spectrum using a portion of the beat signal in a frequency rising range wherein the frequency of the radar wave transmitted from said radar wave transmitter increases and a second spectrum using a portion of the beat signal in a frequency falling range wherein the frequency of the radar wave decreases;

a frequency shift determining circuit determining a plurality of frequency shifts for shifting one of the first and second spectra as a function of an output of a speed sensor measuring a speed of a vehicle equipped with the FM-CW radar, said frequency shift determining circuit correcting the frequency shifts for compensating for an error in the output of the speed sensor;

a frequency moving circuit moving frequency components having peaks in one of the first and second spectra by the corrected frequency shifts to form spectrum groups each consisting of the frequency components moved by one of the corrected frequency shifts and frequency components having peaks in the other of the first and second spectra;

a matching determining circuit determining a measure of matching between a spectrum made up of the moved frequency components and the other of the first and second spectra in each of the spectrum groups to select one of the spectrum groups showing the highest measure of matching;

an optimum frequency shift determining circuit determining one of the frequency shifts determined by said frequency shift determining circuit corresponding to the one of the spectrum groups selected by said matching determining circuit as an optimum frequency shift; and

s

a target motion determining circuit determining a state of motion of the target object based on the frequency components in the frequency rising and falling ranges in the one of the spectrum groups corresponding to the optimum frequency shift.

2. An FM-CW radar apparatus as set forth in claim 1, wherein the frequency shifts determined by said frequency shift determining circuit are a basic frequency shift determined as a function of the speed of the vehicle and sub-frequency shifts different from the basic frequency shift by given amount.

3. An FM-CW radar apparatus as set forth in claim 1, wherein said frequency moving circuit pairs each of the moved frequency components in the one of the first and second spectra with a corresponding one of the frequency components in the other of the first and second spectra in each of the spectrum group, and wherein said matching determining circuit determines a measure of matching between the frequency components of each pair in each of the spectrum groups to select the one of the spectrum groups showing the highest measure of matching.

4. An FM-CW radar apparatus as set forth in claim 3, wherein said target motion determining circuit determines whether the target object is a stationary object or not based on each measure of matching between one of the frequency components in the first spectrum and a corresponding one of the frequency components in the second spectrum paired in the one of the spectrum groups corresponding to the optimum frequency shift.

5. An FM-CW radar apparatus as set forth in claim 3, wherein said matching determining circuit determines the measure of matching between portions of the frequency components paired in each of the spectrum groups within a preselected bandwidth across each of the peaks of the frequency components.

6. An FM-CW radar apparatus as set forth in claim 3, wherein said matching determining circuit determines the measure of matching between the frequency components based on information on an amplitude of each of the frequency components and an azimuth angle of the target object.

7. An FM-CW radar apparatus as set forth in claim 6, wherein said radar wave receiver has two receiving channels, and wherein said information is given by an absolute value of a vector sum of an amplitude evaluation value determined by the amplitude of each of the frequency components and a phase difference evaluation value determined by a phase difference between the frequency components derived through the two receiving channels.

8. An FM-CW radar apparatus as set forth in claim 3, wherein said radar wave receiver has two receiving channels, and wherein said matching determining circuit calculates an absolute value of a vector sum of an amplitude evaluation value determined by an amplitude of each of frequency elements defined across the peak of each of the frequency components within a given bandwidth and a phase difference evaluation value determined by a phase difference between corresponding two of the frequency elements of the frequency components derived through the two receiving channels and sums up the absolute values of the vector sums in each of the frequency components to produce a first sum value, said matching determining circuit also summing up the first sum values in each of the spectrum groups to produce a second sum value and selecting one of the spectrum groups showing the smallest of the second sum values as the one showing the highest measure of matching.

9. An FM-CW radar apparatus as set forth in claim 8, wherein said target motion determining circuit determines that the target object is a stationary object when a selected one of the first sum values is smaller than a threshold value.

10. An FM-CW radar apparatus as set forth in claim 1, wherein said frequency shift determining circuit also determines the frequency shifts as a function of an angular direction of the radar wave transmitted from said radar wave transmitter.

11. An FM-CW radar apparatus as set forth in claim 1, wherein said target motion determining circuit determines, in a cycle, whether the target object is a stationary object or a moving object, estimates a position at which the frequency component arising from the target object determined as the moving object would exist in a subsequent cycle, and sets an estimated moving object flag at said position, and wherein said target motion determining circuit does not determine, in the subsequent cycle, the target object as the stationary object based on the frequency component appearing at the position at which the estimated moving object flag is set.

12. An FM-CW radar as set forth in claim 1, wherein said matching determining circuit determines the measure of matching based on information on peaks of the frequency components.

13. An FM-CW radar apparatus as set forth in claim 12, wherein said information is information on one of frequencies of the peaks, levels of the peaks, and phase differences of the peaks.

36. A storage medium storing means for performing operations of any one of the FM-CW radar apparatuses as set forth in claims 1, 14, 23, 30, 31, and 32.

14. An FM-CW radar for a vehicle comprising:

a radar wave transmitter transmitting a radar wave in the form of a radar beam which has a frequency modulated so as to increase at a given rate and decrease at a given rate cyclically;

a radar wave receiver receiving a return of the radar wave from a target object present in a radar detection zone to mix the return of the radar wave with the radar wave transmitted from said radar wave transmitter to produce a beat signal;

a spectrum producing circuit producing a first spectrum using a portion of the beat signal in a frequency rising range wherein the frequency of the radar wave transmitted from said radar wave transmitter increases and a second spectrum using a portion of the beat signal in a frequency falling range wherein the frequency of the radar wave decreases;

a frequency shift determining circuit determining a frequency shifts for shifting one of the first and second spectra as a function of an output of a speed sensor measuring a speed of a vehicle equipped with the FM-CW radar, said frequency shift determining circuit correcting the frequency shift as a function of an angular direction of the radar beam transmitted from said radar wave transmitter;

a frequency moving circuit moving frequency components having peaks in one of the first and second spectra by the corrected frequency shift to pair each of the moved frequency components in the one of the first and second spectra with a corresponding one of the frequency components in the other of the first and second spectra; and

a target motion determining circuit determining a state of motion of the target object based on the frequency components paired by said frequency moving circuit.

15. An FM-CW radar apparatus as set forth in claim 14, further comprising a matching determining circuit determining a measure of matching between the frequency components forming each pair, and wherein said target motion determining circuit determines the state of motion of the target object based on the measures of matching determined by said matching determining circuit.

16. An FM-CW radar apparatus as set forth in claim 15, wherein said matching determining circuit determines the measure of matching between portions of the paired frequency components within a preselected bandwidth across each of the peaks of the frequency components.

17. An FM-CW radar apparatus as set forth in claim 15, wherein said matching determining circuit determines the measure of matching between the frequency components based on information on an amplitude of each of the frequency components and an azimuth angle of the target object.

18. An FM-CW radar apparatus as set forth in claim 17, wherein said radar wave receiver has two receiving channels, and wherein said information is given by an absolute value of a vector sum of an amplitude evaluation value determined by the amplitude of each of the frequency components and a phase difference evaluation value determined by a phase difference between the frequency components derived through the two receiving channels.

19. An FM-CW radar apparatus as set forth in claim 17, wherein said radar wave receiver has two receiving channels and wherein said matching determining circuit calculates an absolute value of a vector sum of an amplitude evaluation value determined by an amplitude of each of frequency elements defined across the peak of each of the frequency components within a given bandwidth and a phase difference evaluation value determined by a phase difference between corresponding two of the frequency elements of the frequency components derived through the two receiving channels and sums up the absolute values of the vector sums in each of the frequency components to produce a sum value, and wherein said target motion determining circuit determines that the target object is the stationary object when a selected one of the sum values is smaller than a threshold value.

20. An FM-CW radar apparatus as set forth in claim 14, wherein said target motion determining circuit determines, in a cycle, whether the target object is a stationary object or a moving object, estimates a position at which the frequency component arising from the target object determined as the moving object would exist in a subsequent cycle, and sets an estimated moving object flag at said position, and wherein said target motion determining circuit does not determine, in the subsequent cycle, the target object as the stationary object based on the frequency component appearing at the position at which the estimated moving object flag is set.

21. An FM-CW radar as set forth in claim 15, wherein said matching determining circuit determines the measure of matching based on information on peaks of the paired frequency components.

22. An FM-CW radar apparatus as set forth in claim 21, wherein said information is information on one of frequencies of the peaks, levels of the peaks, and phase differences of the peaks.

23. An FM-CW radar comprising:

a radar wave transmitter transmitting a radar wave in the form of a radar beam which has a frequency modulated so as to increase at a given rate and decrease at a given rate cyclically;

a radar wave receiver receiving a return of the radar wave from a target object present in a radar detection zone to mix the return of the radar wave with the radar wave transmitted from said radar wave transmitter to produce a beat signal;

a spectrum producing circuit producing a first spectrum using a portion of the beat signal in a frequency rising range wherein the frequency of the radar wave transmitted from said radar wave transmitter increases and a second spectrum using a portion of the beat signal in a frequency falling range wherein the frequency of the radar wave decreases;

a frequency moving circuit moving frequency components having peaks in one of the first and second spectra by a preselected frequency shift to pair each of the moved frequency components in the one of the first and second spectra with a corresponding one of the frequency components in the other of the first and second spectra;

a matching determining circuit determining a measure of matching between the frequency components forming each pair based on information on an amplitude of each of the frequency components and an azimuth angle of the target object; and

a target motion determining circuit determining a state of motion of the target object based on the measures of matching determined by said matching determining circuit.

24. An FM-CW radar apparatus as set forth in claim 23, wherein said matching determining circuit determines the measure of matching between portions of the paired frequency components within a preselected bandwidth across each of the peaks of the frequency components.

25. An FM-CW radar apparatus as set forth in claim 23, wherein said radar wave receiver has two receiving channels, and wherein said information is given by an absolute value of a vector sum of an amplitude evaluation value determined by the amplitude of each of the frequency components and a phase difference evaluation value determined by a phase difference between the frequency components derived through the two receiving channels.

26. An FM-CW radar apparatus as set forth in claim 23, wherein said radar wave receiver has two receiving channels, and wherein said matching determining circuit calculates an absolute value of a vector sum of an amplitude evaluation value determined by an amplitude of each of frequency elements defined across the peak of each of the frequency components within a given bandwidth and a phase difference evaluation value determined by a phase difference between corresponding two of the frequency elements of the frequency components derived through the two receiving channels and sums up the absolute values of the vector sums in each of the frequency components to produce a sum value, and wherein said target motion determining circuit determines that the target object is the stationary object when a selected one of the sum values is smaller than a threshold value.

27. An FM-CW radar apparatus as set forth in claim 23, wherein said target motion determining circuit determines, in a cycle, whether the target object is a stationary object or a moving object, estimates a position at which the frequency component arising from the target object determined as the moving object would exist in a subsequent cycle, and sets an estimated moving object flag at said position, and wherein said target motion determining circuit does not determine, in the subsequent cycle, the target object as the stationary object based on the frequency component appearing at the position at which the estimated moving object flag is set.

28. An FM-CW radar as set forth in claim 23, wherein said matching determining circuit determines the measure of matching based on information on peaks of the paired frequency components.

29. An FM-CW radar apparatus as set forth in claim 28, wherein said information is information on one of frequencies of the peaks, levels of the peaks, and phase differences of the peaks.

30. An FM-CW radar comprising:

a radar wave transmitter transmitting a radar wave in the form of a radar beam which has a frequency modulated so as to increase at a given rate and decrease at a given rate cyclically;

a radar wave receiver receiving a return of the radar wave from a target object present in a radar detection zone to mix the return of the radar wave with the radar wave transmitted from said radar wave transmitter to produce a beat signal;

a spectrum producing circuit producing a first spectrum using a portion of the beat signal in a frequency rising range wherein the frequency of the radar wave transmitted from said radar wave transmitter increases and a second spectrum using a portion of the beat signal in a frequency falling range wherein the frequency of the radar wave decreases;

a frequency moving circuit moving frequency components having peaks in one of the first and second spectra by a preselected frequency shift to pair each of the moved frequency components in the one of the first and second spectra with a corresponding one of the frequency components in the other of the first and second spectra; and

a target motion determining circuit comparing the frequency components forming each pair to determine a state of motion of the target object, said target motion determining circuit determining, in a cycle, whether the target object is a stationary object or a moving object, estimating a position at which the frequency component arising from the target object determined as the moving object would exist in a subsequent cycle, and setting an estimated moving object flag at said position, said target motion determining circuit not determining, in the subsequent cycle, the target object as the stationary object based on the frequency component appearing at the position at which the estimated moving object flag is set.

31. An FM-CW radar apparatus for a vehicle comprising:

a radar wave transmitter transmitting a radar wave having a frequency modulated so as to increase at a given rate and decrease at a given rate cyclically;

a radar wave receiver receiving a return of the radar wave from a target object present in a radar detection zone to mix the return of the radar wave with the radar wave transmitted from said radar wave transmitter to produce a beat signal;

a spectrum producing circuit producing a first spectrum using a portion of the beat signal in a frequency rising range wherein the frequency of the radar wave transmitted from said radar wave transmitter increases and a second spectrum using a portion of the beat signal in a frequency falling range wherein the frequency of the radar wave decreases;

a frequency shift determining circuit determining a frequency shift for shifting one of the first and second spectra as a function of a speed of a vehicle equipped with the FM-CW radar;

a frequency moving circuit moving frequency components having peaks in one of the first and second spectra by the frequency shift to form pairs each consisting of one of the frequency components moved by the frequency shift and a corresponding one of frequency components having peaks in the other of the first and second spectra;

a matching determining circuit determining a measure of matching between a spectrum made up of the frequency components moved by said frequency moving circuit and the other of the first and second spectra based on information on portions of the frequency components within a preselected bandwidth across each of the peaks of the frequency components in one of the first and second spectra selected as a reference; and

a target motion determining circuit determining a state of motion of the target object based on the pairs of the frequency components.

32. An FM-CW radar apparatus for a vehicle comprising:

a radar wave transmitter transmitting a radar wave having a frequency modulated so as to increase at a given rate and decrease at a given rate cyclically;

a radar wave receiver receiving a return of the radar wave from a target object present in a radar detection zone to mix the return of the radar wave with the radar wave transmitted from said radar wave transmitter to produce a beat signal;

a spectrum producing circuit producing a first spectrum using a portion of the beat signal in a frequency rising range wherein the frequency of the radar wave transmitted from said radar wave transmitter increases and a second spectrum using a portion of the beat signal in a frequency falling range wherein the frequency of the radar wave decreases;

a frequency shift determining circuit determining a frequency shift for shifting one of the first and second spectra as a function of a speed of a vehicle equipped with the FM-CW radar;

a frequency moving circuit moving frequency components having peaks in one of the first and second spectra within a range of the frequency shift±

a given frequency band; and

a matching determining circuit determining a measure of matching between a spectrum made up of the frequency components moved by said frequency moving circuit and the other of the first and second spectra based on information on the peaks of the frequency components of the first and second spectra.

33. An FM-CW radar apparatus as set forth in claim 32, wherein said information is information on one of frequencies of the peaks, levels of the peaks, and phase differences of the peaks.

34. An FM-CW radar apparatus as set forth in claim 32, wherein said radar wave receiver has two receiving channels, and wherein said matching determining circuit determines the measure of matching based on an absolute value of a vector sum of an amplitude evaluation value determined by the amplitude of each of the frequency components and a phase difference evaluation value determined by a phase difference between the frequency components derived through the two receiving channels.

35. An FM-CW radar apparatus as set forth in claim 34, further comprising a target motion determining circuit which determines that the target object is a stationary object when a selected one of the absolute values is smaller than a threshold value.

37. An FM-CW radar apparatus for a vehicle comprising:

a radar wave transmitter transmitting a radar wave in the form of a transmit signal which has a frequency modulated so as to increase at a given rate and decrease at a given rate cyclically;

a radar wave receiver receiving a return of the radar wave from a target object present in a radar detection zone to mix the return of the radar wave with the radar wave transmitted from said radar wave transmitter to produce a beat signal;

a spectrum producing circuit producing a first spectrum using a portion of the beat signal in a frequency rising range wherein the frequency of the radar wave transmitted from said radar wave transmitter increases and a second spectrum using a portion of the beat signal in a frequency falling range wherein the frequency of the radar wave decreases;

a frequency shift determining circuit determining a plurality of frequency shifts for shifting one of the first and second spectra as a function of a speed of a vehicle equipped with the FM-CW radar measured by a speed sensor, said frequency shift determining circuit correcting the frequency shifts for compensating for an error in measurement of the speed sensor;

a frequency moving circuit moving frequency components having peaks in one of the first and second spectra by the corrected frequency shifts to form spectrum groups each consisting of the frequency components moved by one of the corrected frequency shifts and frequency components having peaks in the other of the first and second spectra;

a matching determining circuit determining a measure of matching between a spectrum made up of the moved frequency components and the other of the first and second spectra in each of the spectrum groups to select one of the spectrum groups showing the highest measure of matching;

an optimum frequency shift determining circuit determining one of the frequency shifts determined by said frequency shift determining circuit corresponding to the one of the spectrum groups selected by said matching determining circuit as an optimum frequency shift; and

an estimating circuit estimating an actual speed of the vehicle by correcting the speed of the vehicle measured by the speed sensor using the optimum frequency shift.

38. An FM-CW radar apparatus as set forth in claim 37, wherein said estimating circuit estimates the actual speed of the vehicle according to an equation below

39. An FM-CW radar apparatus as set forth in claim 37, wherein said frequency shift determining circuit corrects the frequency shifts based on the actual speed estimated by said estimating circuit.

40. An FM-CW radar apparatus as set forth in claim 37, wherein said estimating circuit estimates the actual speed in a cycle, determines an actual acceleration value based on a difference between the actual speed estimated in this cycle and the actual speed estimated one cycle earlier, and estimates an actual speed of the vehicle in a subsequent cycle, and wherein said frequency shift determining circuit corrects the frequency shifts based on the estimated actual speed in the subsequent cycle.

41. An FM-CW radar apparatus as set forth in claim 37, wherein the frequency shifts determined by said frequency shift determining circuit are a basic frequency shift determined as a function of the speed of the vehicle and sub-frequency shifts different from the basic frequency shift by given amount.

42. An FM-CW radar apparatus as set forth in claim 37, wherein said frequency shift determining circuit also determines the frequency shifts as a function of an angular direction of the radar wave transmitted from said radar wave transmitter.

43. An FM-CW radar apparatus as set forth in claim 37, wherein said frequency moving circuit pairs each of the moved frequency components in the one of the first and second spectra with a corresponding one of the frequency components in the other of the first and second spectra in each of the spectrum group, and wherein said matching determining circuit determines a measure of matching between the frequency components forming each pair in each of the spectrum groups to select the one of the spectrum groups showing the highest measure of matching.

44. An FM-CW radar apparatus as set forth in claim 43, further comprising a target motion determining circuit which determines whether the target object is a stationary object or not based on each measure of matching between one of the frequency components in the first spectrum and a corresponding one of the frequency components in the second spectrum paired in the one of the spectrum groups corresponding to the optimum frequency shift.

45. An FM-CW radar apparatus as set forth in claim 44, wherein said target motion determining circuit determines, in a cycle, whether the target object is a stationary object or a moving object, estimates a position at which the frequency component arising from the target object determined as the moving object would exist in a subsequent cycle, and sets an estimated moving object flag at said position, and wherein said target motion determining circuit does not determine, in the subsequent cycle, the target object as the stationary object based on the frequency component appearing at the position at which the estimated moving object flag is set.

46. An FM-CW radar apparatus as set forth in claim 44, wherein said target motion determining circuit compares the actual speed estimated by said estimating circuit with a relative speed of the target object to the vehicle and reflects a result of the comparison on determination of whether the target object is the stationary object or the moving object.

47. An FM-CW radar apparatus as set forth in claim 37, wherein said matching determining circuit determines the measure of matching based on information on at least one of an amplitude of each of the frequency components and an azimuth angle of the target object.

48. An FM-CW radar apparatus as set forth in claim 47, wherein said radar wave receiver has two receiving channels, and wherein said information is given by an absolute value of a vector sum of an amplitude evaluation value determined by the amplitude of each of the frequency components and a phase difference evaluation value determined by a phase difference between the frequency components derived through the two receiving channels.

49. An FM-CW radar apparatus as set forth in claim 47, wherein said radar wave receiver has two receiving channels, and wherein said matching determining circuit calculates an absolute value of a vector sum of an amplitude evaluation value determined by an amplitude of each of frequency elements defined across the peak of each of the frequency components within a given bandwidth and a phase difference evaluation value determined by a phase difference between corresponding two of the frequency elements of the frequency components derived through the two receiving channels and sums up the absolute values of the vector sums in each of the frequency components to produce a first sum value, said matching determining circuit also summing up the first sum values in each of the spectrum groups to produce a second sum value and selecting one of the spectrum groups showing the smallest of the second sum values as the one showing the highest measure of matching.

50. An FM-CW radar apparatus as set forth in claim 49, further comprising a target motion determining circuit which determines that the target object is a stationary object when a selected one of the first sum values is smaller than a threshold value.