Radar altimeter

• US 6,992,614 B1
• Filed: 04/22/2004
• Issued: 01/31/2006
• Est. Priority Date: 04/22/2004
• Status: Expired due to Fees

• Current Assignee: Honeywell International Inc.
• Original Assignee: Honeywell International Inc.
• Inventors: Joyce, James W.
• Primary Examiner(s): Lobo, Ian J.
• Application Number:
  US10/829,849
• Time in Patent Office: 649 Days
• Field of Search: 342/120, 342/121, 342/122, 342/123
• US Class Current: 342/122
• CPC Class Codes: G01S 13/34 using transmission of continuous, frequency-modulated waves while heterodyning the received signal, or a signal derived therefrom, with a locally-generated signal related to the contemporaneously transmitted signal
• CPC Class Codes: G01S 13/882 for altimeters measuring height using barometric means G01C5/06
• CPC Class Codes: G01S 7/352 Receivers

Abstract

A radar altimeter is provided that includes a transmitter operable to generate a radio signal at a modulation frequency, and transmit the radio signal toward a ground surface for reflection therefrom to thereby propagate a reflected radio signal. The radar altimeter also includes a receiver operable to receive the reflected radio signal, and determine the altitude of the aircraft based on the modulation frequency of the radio signal and a difference frequency derived from the radio signal and the reflected radio signal. The receiver is also operable to control the transmitter so as to vary the modulation frequency of the radio signal based on the altitude of the aircraft. Preferably, the modulation frequency of the radio signal is greater at lower altitudes than at higher altitudes.

Claims

1. A radar altimeter for determining an altitude of an aircraft, comprising:

a first antenna;

a second antenna;

a transmitter coupled to said first antenna and operable to generate a radio signal at a modulation frequency and transmit said radio signal, via said first antenna, toward a ground surface for reflection therefrom to thereby propagate a reflected radio signal; and

a receiver coupled to said second antenna and configured to receive, via said second antenna, said reflected radio signal and an antenna coupling signal generated between said first and said second antenna, the receiver operable to (i) determine said altitude of said aircraft based on said modulation frequency of said radio signal and a difference frequency derived from said radio signal and said reflected radio signal and (ii) control said transmitter so as to vary said modulation frequency of said radio signal based on said altitude of said aircraft, said receiver comprising;

a mixer operable to (i) mix said radio signal with said reflected radio signal and said antenna coupling signal to thereby generate a mixed signal and (ii) demodulate said mixed signal into a baseband difference signal and a baseband antenna coupling signal, and

a filter operable to attenuate said baseband antenna coupling signal and pass said baseband difference signal without attenuation.

2. The radar altimeter of claim 1, wherein said radio signal comprises a frequency modulated continuous wave radio signal.

3. The radar altimeter of claim 1, wherein said altitude of said aircraft is determined based on said difference frequency derived from said radio signal being transmitted at a specified time and said reflected radio signal being received at said specified time.

4. The radar altimeter of claim 1, wherein said modulation frequency of said radio signal is varied when said altitude of said aircraft reaches at least one threshold altitude.

5. The radar altimeter of claim 4, wherein said modulation frequency of said radio signal is greater at altitudes below said threshold altitude than at altitudes above said threshold altitude.

6. The radar altimeter of claim 1, wherein said transmitter comprises:

a variable rate modulator operable to generate a voltage waveform; and

a voltage controlled oscillator operable to generate said radio signal at said modulation frequency, wherein said modulation frequency is controlled by said voltage waveform from said variable rate modulator.

7. The radar altimeter of claim 6, wherein said receiver comprises a microprocessor operable to control said variable rate modulator so as to vary said modulation frequency of said radio signal based on said altitude of said aircraft.

8. The radar altimeter of claim 1, wherein said filter comprises a fixed filter having a single frequency response for all altitudes of said aircraft.

9. The radar altimeter of claim 1, wherein said receiver further comprises:

an analog-to-digital converter operable to convert said baseband difference signal to a digital difference signal;

a digital signal processor operable to determine said difference frequency from said digital difference signal and correlate said difference frequency to said altitude of said aircraft for said modulation frequency; and

a microprocessor operable to control said transmitter so as to vary said modulation frequency of said radio signal based on said altitude of said aircraft.

10. The radar altimeter of claim 9, wherein said microprocessor is also operable to output said altitude of said aircraft to a display of said altimeter.

11. A method of determining an altitude of an aircraft, comprising:

generating a radio signal at a modulation frequency;

transmitting said radio signal toward a ground surface for reflection therefrom to thereby propagate a reflected radio signal;

receiving said reflected radio signal and, upon receipt thereof, generating an antenna coupling signal;

mixing said radio signal with said reflected radio signal and said antenna coupling signal to thereby generate a mixed signal;

demodulating said mixed signal into a baseband difference signal and a baseband antenna coupling signal;

attenuating said baseband antenna coupling signal and passing said baseband difference signal without attenuation;

determining said altitude of said aircraft based on said modulation frequency of said radio signal and a difference frequency derived from said radio signal and said reflected radio signal;

and

varying said modulation frequency of said radio signal based on said altitude of said aircraft.

12. The method of claim 11, wherein said altitude of said aircraft is determined based on said difference frequency derived from said radio signal being transmitted at a specified time and said reflected radio signal being received at said specified time.

13. The method of claim 11, wherein said modulation frequency of said radio signal is varied when said altitude of said aircraft reaches at least one threshold altitude.

14. The method of claim 13, wherein said modulation frequency of said radio signal is greater at altitudes below said threshold altitude than at altitudes above said threshold altitude.

15. The method of claim 11, further comprising:

generating a voltage waveform to control said modulation frequency of said radio signal;

generating said radio signal at said modulation frequency controlled by said voltage waveform; and

varying said voltage waveform based on said altitude of said aircraft so as to vary said modulation fluency of said radio signal.

16. The method of claim 11, wherein said attenuating is performed by a fixed filter having a single frequency response for all altitudes of said aircraft.

17. The method of claim 11, wherein said method further comprises:

converting said baseband difference signal to a digital difference signal;

determining said difference frequency from said digital difference signal;

correlating said difference frequency to said altitude of said aircraft for said modulation frequency; and

varying said modulation frequency based on said altitude of said aircraft.

18. A radar altimeter for determining an altitude of an aircraft, comprising:

means for generating a radio signal at a modulation frequency;

means for transmitting said radio signal toward a ground surface for reflection therefrom to thereby propagate a reflected radio signal;

means for receiving said reflected radio signal and an antenna coupling signal;

means for (i) mixing said radio signal with said reflected radio signal and said antenna coupling signal to thereby generate a mixed signal and (ii) demodulating said mixed signal into a baseband difference signal and a baseband antenna coupling signal,

means for (i) attenuating said baseband antenna coupling signal and (ii) passing said baseband difference signal without attenuation;

means for determining said altitude of said aircraft based on said modulation frequency of said radio signal and a difference frequency derived from said radio signal and said reflected radio signal; and

means for varying said modulation frequency of said radio signal based on said altitude of said aircraft.

19. The radar altimeter of claim 18, wherein said radio signal comprises a frequency modulated continuous wave radio signal.

20. The radar altimeter of claim 18, wherein said altitude of said aircraft is determined based on said difference frequency derived from said radio signal being transmitted at a specified time and said reflected radio signal being received at said specified time.

21. The radar altimeter of claim 18, wherein said modulation frequency of said radio signal is varied when said altitude of said aircraft reaches at least one threshold altitude.

22. The radar altimeter of claim 21, wherein said modulation frequency of said radio signal is greater at altitudes below said threshold altitude than at altitudes above said threshold altitude.

23. A radar altimeter for determining an altitude of an aircraft, comprising:

a variable rate modulator operable to generate a voltage waveform;

a voltage controlled oscillator operable to generate a frequency modulated continuous wave radio signal at a modulation frequency controlled by said voltage waveform from said variable rate modulator;

a transmitter antenna operable to transmit said radio signal toward a ground surface for reflection therefrom to thereby propagate a reflected radio signal;

a receiver antenna operable to receive said reflected radio signal, wherein said receiver antenna also receives an antenna coupling signal generated between said transmitter antenna and said receiver antenna;

a mixer operable to mix said radio signal with said reflected radio signal and said antenna coupling signal to thereby generate a mixed signal, said mixer also operable to demodulate said mixed signal into a baseband difference signal and a baseband antenna coupling signal;

a filter operable to attenuate said baseband antenna coupling signal and pass said baseband difference signal without attenuation;

an analog-to-digital converter operable to convert said baseband difference signal to a digital difference signal;

a digital signal processor operable to determine a difference frequency from said digital difference signal and correlate said difference frequency to said altitude of said aircraft for said modulation frequency; and

a microprocessor operable to control said variable rate modulator so as to vary said modulation frequency of said radio signal based on said altitude of said aircraft.

24. The radar altimeter of claim 23, wherein said altitude of said aircraft is determined based on said difference frequency derived from said radio signal being transmitted at a specified time and said reflected radio signal being received at said specified time.

25. The radar altimeter of claim 23, wherein said modulation frequency of said radio signal is varied when said altitude of said aircraft reaches at least one threshold altitude.

26. The altimeter of claim 25, wherein said modulation frequency of said radio signal is greater at altitudes below said threshold altitude than at altitudes above said threshold altitude.

27. The radar altimeter of claim 23, wherein said filter comprises a fixed filter having a single frequency response for all altitudes of said aircraft.