Radar altimeter

• US 7,239,266 B2
• Filed: 08/26/2004
• Issued: 07/03/2007
• Est. Priority Date: 08/26/2004
• Status: Active Grant

• Current Assignee: Honeywell International Inc.
• Original Assignee: Honeywell International Inc.
• Inventors: Vacanti, David C.
• Primary Examiner(s): Tarcza; Thomas H.
• Assistant Examiner(s): Barker; Matthew M.
• Application Number:
  US10/926,676
• Publication Number:
  US 20060044182A1
• Time in Patent Office: 1,041 Days
• Field of Search: 342/120
• US Class Current: 342/120
• CPC Class Codes: G01S 13/882 for altimeters measuring height using barometric means G01C5/06
• CPC Class Codes: G01S 7/032 Constructional details for solid-state radar subsystems
• CPC Class Codes: G01S 7/034 Duplexers switching devices for waveguides H01P1/10; transmit-receive switching in transceivers H04B1/44
• CPC Class Codes: G01S 7/038 Feedthrough nulling circuits
• CPC Class Codes: G01S 7/35 Details of non-pulse systems

Abstract

The present invention provides a radar altimeter system with a closed loop modulation for generating more accurate radar altimeter values. The system includes an antenna, a circulator, a receiver, and a transmitter. The circulator receives or sends a radar signal from/to the antenna. The receiver receives the received radar signal via the circulator. The transmitter generates a radar signal and includes a phase-locked loop circuit for generating the radar signal based on a pre-defined phase signal. The transmitter includes a direct digital synthesizer that generates the phase signal based on a pre-defined clock signal and a control signal. The system includes a digital signal processor and a tail strike warning processor that determine position of a tail of the aircraft relative to ground and present an alert if a warning condition exists based on the determined position of the tail of the aircraft and a predefined threshold.

Claims

1. A radar system on an aircraft, the system comprising:

an antenna for outputting and receiving a radar signal;

a circulator in signal communication with the antenna;

a receiver for receiving the radar signal via the circulator; and

a transmitter for generating a radar signal, the transmitter comprising;

a phased-lock loop circuit for generating the radar signal;

a direct digital synthesizer for generating a reference signal based on a pre-defined clock signal and a control signal;

an oscillator and multiplier component for generating a clock signal; and

a mixer for offsetting the reference signal by combining the reference signal with the clock signal,

wherein the phased-lock loop circuit generates the radar signal based on the offset reference signal, wherein the offset reference signal is greater than at least 30 MHz.

2. The system of claim 1, wherein the antenna is a micro-strip antenna.

3. The system claim 2, wherein the circulator, the receiver, and the transmitter are formed on a circuit board, the circuit board being connected to the antenna, wherein the circulator and antenna are connected by printed wiring.

4. The system claim 3, wherein the distance between the circuit board and the antenna is less than one inch.

5. The system of claim 3, further comprising:

a housing for hermetically sealing the circuit board.

6. The system of claim 5, further comprising an analog-to-digital converter for converting the signal received by the receiver into a digital signal, wherein the converter is formed on the circuit board.

7. The system of claim 6, further comprising:

a component for generating the control signal and for processing the digital signal, wherein the component is remotely located from the housing.

8. The system of claim 7, wherein the component is located in an electronics bay of the aircraft.

9. The system of claim 7, further comprising:

a tail strike warning component in signal communication with the component for determining position of a tail of the aircraft relative to ground based on the processed digital signal.

10. The system of claim 9, further comprising:

an output device in signal communication with the tail strike warning processor for presenting an alert if the tail strike warning processor has determined that a warning condition exists based on the determined position of the tail of the aircraft and a predefined threshold.

11. The system of claim 1, wherein the transmitter produces a modulated radar signal having a linearity error less than 0.5%.

12. The system of claim 7, wherein modulation quality of transmitter remains constant over time.

13. The system of claim 7, wherein a signal-to-noise ratio associated with processing of the digital signal remains constant over time.

14. A method performed by a radar altimeter system on an aircraft, the method comprising:

generating a clock signal;

generating a reference signal using a direct digital synthesizer;

offsetting the reference signal by combining the reference signal with the clock signal;

generating a radar signal using a transmitter having a closed loop circuit that receives the offset reference signal;

outputting the generated radar signal via an antenna; and

receiving a radar signal at a receiver via the antenna, wherein the offset reference signal is greater than at least 30 MHz.

15. The method of claim 14, further comprising:

converting the signal received by the receiver into a digital signal;

sending the digital signal to a component; and

determining at the component an altitude value based on the digital signal;

generating the control signal based on the digital signal,

wherein the component is remotely located from the receiver, transmitter, and antenna.

16. The method of claim 15, wherein the component is located in an electronics bay of the aircraft.

17. The method of claim 15, further comprising:

presenting an alert if the altitude value is below a threshold value.

18. The method of claim 14, wherein the closed-loop circuit is a phased-locked loop circuit.

19. The method of claim 14, wherein the generated radar signal has a linearity error less than 0.5%.

20. The method of claim 14, wherein modulation quality of the radar signal remains constant over time.