Cable phase calibration in a TCAS

• US 6,392,598 B1
• Filed: 05/12/2000
• Issued: 05/21/2002
• Est. Priority Date: 02/01/2000
• Status: Expired due to Term

• Current Assignee: Honeywell International Inc.
• Original Assignee: Honeywell International Inc.
• Inventors: Brandao, Ruy L., Jones, James B., Brandao, Ruy C., Ringwald, Rand
• Primary Examiner(s): Blum, Theodore M.
• Application Number:
  US09/570,100
• Time in Patent Office: 739 Days
• Field of Search: 342/442, 342/445, 342/446, 342/174
• US Class Current: 342/442
• CPC Class Codes: G01S 13/933 of aircraft or spacecraft
• CPC Class Codes: G01S 3/023 Monitoring or calibrating
• CPC Class Codes: G01S 3/48 the waves arriving at the antennas being continuous or intermittent and the phase difference of signals derived therefrom being measured

Abstract

An apparatus and method determining angle-of-arrival of a received radio frequency signal, and apparatus and method for calibrating the angle-of-arrival determining apparatus.

Claims

1. A direction finding antenna system for determining the relative bearing of a signal received by said antenna system, comprising

two pair of spaced apart antenna elements forming respective mutually perpendicular bisecting axes, said antenna elements receiving a signal;

a digital phase detector having a variable phase input port coupled via a transmission channel to the output of each said antenna element and a reference phase input port coupled to a phase generator;

frequency discriminator coupled to the output of said digital phase detector; and

a processor coupled to the output of said frequency discriminator, said processor determining phase corrected data corresponding to signals output by respective ones of said antenna elements and determining a quantity related to the relative bearing to said received signal from the antenna system.

2. The antenna system recited in claim 1, wherein each said transmission channel further comprises:

a transmission line coupling an output of each of said antenna elements to an input of a respective receiver element; and

an analog-to-digital converter coupled between the output of said receiver element and a respective one of said variable phase input ports.

3. A direction finding antenna system for determining the relative bearing of a signal received by said antenna system, comprising

two pair of spaced apart antenna elements forming respective mutually perpendicular bisecting axes, said antenna elements receiving a signal;

a transmission line coupling an output of each of said antenna elements to an input of a respective receiver element;

an analog-to-digital converter coupled to the output of each of said receiver elements;

a digital phase detector having a variable phase input port coupled to the output of each said analog-to-digital converters and a reference phase input port coupled to a reference phase generator;

frequency discriminator coupled to the output of said digital phase detector; and

a processor coupled to the output of said frequency discriminator, said processor determining phase corrected data corresponding to signals output by respective ones of said antenna elements and determining a quantity related to the relative bearing to said received signal from the antenna system.

4. The antenna system recited in claim 3, further comprising:

a transmitter coupled to each said antenna element via a respective one of said transmission lines; and

a calibration signal alternately coupled to an input of each said transmitter.

5. The antenna system recited in claim 4, further comprising a modulator coupled to each said transmitter.

6. The antenna system recited in claim 5, further comprising:

a memory coupled to said processor; and

correction data stored at a location in said memory.

7. The antenna system recited in claim 6, wherein said location of said correction data in said memory is a function of a frequency of said received signal as determined by said frequency discriminator.

8. The antenna system recited in claim 7, wherein said correction data further comprises one of a correction factor and a phase corrected value.

9. The antenna system recited in claim 8, wherein said calibration signal further comprises a plurality of calibration signals including at least a first signal having a frequency essentially the same as a minimum extreme of a range of said received signal and a second signal having a frequency essentially the same as a maximum extreme of said range of said received signal.

10. A direction finding antenna system for determining the relative bearing of a signal received by said antenna system, comprising

first, second, third and fourth spaced apart antennas mounted in cruciform configuration;

first, second, third and fourth receivers coupled to respective ones of said first, second, third and fourth antennas for amplifying, converting and limiting radio frequency signals received by said first, second, third and fourth antennas;

first, second, third and fourth analog-to-digital converters coupled to receive the output of respective ones of said first, second, third and fourth receivers, each of said first, second, third and fourth analog-to-digital converters outputting sequential output signals;

a digital phase detector having a plurality of variable phase input ports each coupled to simultaneously receive said sequential output signals of respective ones of said first, second, third and fourth analog-to-digital converters and a reference phase input port coupled to a reference phase generator for receiving a reference phase output signal thereof, said digital phase detector generating I and Q data from said reference phase and respective ones of said signals received by said first, second, third and fourth antennas; and

a processor coupled to receive said I and Q data from said digital phase detector, said processor including a frequency discriminator for comparing sequential output signals of respective ones of said first, second, third and fourth analog-to-digital converters and determining a frequency of each said output signals, said processor determining phase corrected values of said I and Q data and determining a first quantity related to the relative bearing to the received signal from the antenna system as a function of said phase corrected values.

11. The antenna system recited in claim 10, further comprising:

a synthesizer generating a plurality of calibration signals at different frequencies; and

a transmitter coupled to said synthesizer and to one of said antennas for injecting a calibration signal into said antenna.

12. The antenna system recited in claim 11, further comprising a modulator coupled to said transmitter and each of said antennas for alternately applying calibration signals to different ones of said antennas.

13. The antenna system recited in claim 12, further comprising an input memory coupled to said processor and having correction data stored therein, said processor accessing said correction data for determining said phase corrected values of said I and Q data.

14. The antenna system recited in claim 13, wherein said correction data stored in said memory is accessed by said processor as a function of said frequency of said output signals.

15. The antenna system recited in claim 14, wherein said correction data further comprises one or more correction factors.

16. The antenna system recited in claim 14, wherein said correction data further comprises one or more phase corrected values.

17. The antenna system recited in claim 14, wherein said plurality of calibration signals further comprises at least a first signal having a low frequency relative to a nominal value of said received signal and a second signal having a high frequency relative to said nominal value.

18. The antenna system recited in claim 14, wherein said low frequency further comprises a minimum of an allowable range of said received signal and said high frequency further comprises a maximum of said allowable range of said received signal.

19. The antenna system recited in claim 18, wherein said received signal is a transponder signal in the range of 1087 MHz to 1093 MHz.

20. A method for using a direction finding antenna system for determining the relative bearing of a received signal, the method comprising:

receiving a signal into a plurality of spaced apart antenna elements mounted in cruciform configuration;

forming a digital intermediate frequency output signal from said received signal;

comparing a phase of said digital intermediate frequency output signal with a reference phase;

determining a frequency of said intermediate frequency output signal;

determining phase corrected values of said received signal; and

determining a quantity related to the relative bearing to the received signal using said phase corrected values.

21. The method recited in claim 20, wherein said forming a digital intermediate frequency output signal from said received signal further comprises:

forming an analog intermediate frequency output signal from said received signal; and

converting said analog intermediate frequency output signal into said digital intermediate frequency output signal.

22. The method recited in claim 21, further comprising forming in-phase and in-quadrature data from said digital intermediate frequency output signal and said reference phase.

23. The method recited in claim 22, wherein said determining phase corrected values of said received signal further comprises accessing a stored file comprising correction data.

24. The method recited in claim 23, wherein said accessing a stored file comprising correction data further comprises accessing said stored file comprising correction data as a function of said frequency of said intermediate frequency output signal.

25. A method for using a direction finding antenna system for determining the relative bearing of a received signal, the method comprising:

receiving a signal into a plurality of spaced apart antenna elements mounted in cruciform configuration;

amplifying, converting and limiting said received signal and forming an analog intermediate frequency output signal therefrom;

converting said analog intermediate frequency output signal into a digital intermediate frequency output signal and outputting samples of said digital intermediate frequency output signal;

comparing the phase of said digital intermediate frequency output signal samples with a reference phase to form in-phase and in-quadrature data therefrom;

determining a frequency of said digital intermediate frequency output signal samples;

determining phase corrected values of said in-phase and in-quadrature data; and

determining a first quantity related to the relative bearing to the received signal as a function of said phase corrected values.

26. The method recited in claim 25, wherein said determining phase corrected values of said in-phase and in-quadrature data further comprises accessing a stored file comprising correction data.

27. The method recited in claim 26, wherein said determining phase corrected values of said in-phase and in-quadrature data further comprises accessing said stored file comprising correction data as a function of said frequency of said digital intermediate frequency output signal samples.

28. The method recited in claim 27, wherein said determining phase corrected values of said in-phase and in-quadrature data further comprises combining said correction data with said in-phase and in-quadrature data formed from said digital intermediate frequency output signal samples and said reference phase.

29. The method recited in claim 27, wherein said determining phase corrected values of said in-phase and in-quadrature data further comprises substituting said correction data for said in-phase and in-quadrature data formed from said digital intermediate frequency output signal samples and said reference phase.

30. A method for calibrating a direction finding antenna system, the method comprising:

injecting a calibration signal into one of a plurality of antenna elements;

receiving said calibration signal into a different one of said antenna elements;

outputting a digital intermediate frequency signal formed of said received calibration signal;

determining a frequency of said digital intermediate frequency signal;

comparing a phase of said digital intermediate frequency signal to a reference phase; and

determining phase correction data corresponding to said digital intermediate frequency signal.

31. The calibration method recited in claim 30, wherein said calibration signal further comprises a plurality of calibration signals.

32. The calibration method recited in claim 31, wherein each of said plurality of calibration signals further comprises a frequency signal having a frequency in the permissible range of frequencies of the received signal.

33. The calibration method recited in claim 30, further comprising storing said phase correction data.

34. The calibration method recited in claim 30, further comprising storing said phase correction data as a function of a corresponding one of said digital intermediate frequency signals.

35. The calibration method recited in claim 30, wherein said outputting a digital intermediate frequency signal formed of said received calibration signal further comprises:

forming an analog intermediate frequency signal of said received calibration signal; and

converting said analog intermediate frequency signal into a digital intermediate frequency signal.

36. The calibration method recited in claim 30, wherein said comparing a phase of said digital intermediate frequency signal to a reference phase further comprises forming in-phase and in-quadrature data therefrom.

37. A method for calibrating a direction finding antenna system, the method comprising:

alternately injecting a calibration signal into different ones of a plurality of antenna elements;

receiving said calibration signal into others of said antenna elements;

amplifying, converting and limiting said received calibration signal and forming an analog intermediate frequency output signal therefrom;

converting said analog intermediate frequency output signal into a digital intermediate frequency output signal and outputting samples of said digital intermediate frequency output signal;

determining the frequency of said digital intermediate frequency output signal samples;

comparing the phase of said digital intermediate frequency output signal samples with a reference phase to form in-phase and in-quadrature data therefrom; and

determining phase correction data corresponding to said in-phase and in-quadrature data and storing same.

38. The calibration method recited in claim 37, wherein said storing said phase correction data further comprises storing said phase correction data as a function of said intermediate frequency.

39. The calibration method recited in claim 38, wherein said injecting a calibration signal further comprises injecting a plurality of calibration signals.

40. The calibration method recited in claim 39, wherein said plurality of calibration signals further comprises a minimum and a maximum of an allowable range of frequencies of said received signal.

41. The calibration method recited in claim 39, wherein said injecting a calibration signal into one of a plurality of antenna elements further comprises alternately injecting said calibration signal into different ones of said others of said antenna elements.

42. A direction finding antenna system for determining the relative bearing of an intruder aircraft from a protected aircraft in conjunction with a Traffic Alert Collision Avoidance System (TCAS), the intruder aircraft being equipped to transmit signals received by said antenna system, the direction finding antenna system comprising:

two pair of spaced apart antenna elements formed in cruciform configuration to receive a radio frequency signal;

each one of a plurality of receiver elements coupled via a different transmission line to a different one of said antenna elements;

each one of a plurality of analog-to-digital converters coupled to receive the output of a respective one of said receiver elements;

a digital phase detector having a plurality of variable phase input ports each coupled to the output of one of said analog-to-digital converters and a reference phase input port coupled to receive the output of a reference phase generator;

a frequency discriminator coupled to receive the output of said digital phase detector;

a processor coupled to receive the output of said frequency discriminator, said processor determining phase corrected data corresponding to signals output by respective ones of said antenna elements and determining a relative bearing angle to said received radio frequency signal from the antenna system; and

a Traffic Alert Collision Avoidance System coupled to receive said relative bearing angle.

43. The direction finding antenna system recited in claim 42, further comprising:

a transmitter coupled to each said antenna element via a respective one of said transmission lines; and

a calibration signal generator alternately coupled to an input of each said transmitter.

44. The direction finding antenna system recited in claim 43, further comprising a modulator coupled to each said transmitter for alternately coupling said calibration signal generator to an input of each said transmitter.

45. The direction finding antenna system recited in claim 44, further comprising:

a memory coupled to said processor; and

correction data stored at a location in said memory.

46. The direction finding antenna system recited in claim 45, wherein said location of said correction data in said memory is determined as a function of a frequency of said received signal as determined by said frequency discriminator.