False lock filter for pulsed radar altimeters

• US 7,714,774 B2
• Filed: 09/06/2007
• Issued: 05/11/2010
• Est. Priority Date: 09/06/2007
• Status: Active Grant

• Current Assignee: Honeywell International Inc.
• Original Assignee: Honeywell International Inc.
• Inventors: Winstead, Benjamin J.
• Primary Examiner(s): Tarcza; Thomas H
• Assistant Examiner(s): Brainard; Timothy A
• Application Number:
  US11/851,038
• Publication Number:
  US 20090066559A1
• Time in Patent Office: 978 Days
• Field of Search: 342/122
• US Class Current: 342/122
• CPC Class Codes: G01S 13/882 for altimeters measuring height using barometric means G01C5/06
• CPC Class Codes: G01S 7/023 Interference mitigation, e.g. reducing or avoiding non-intentional interference with other HF-transmitters, base station transmitters for mobile communication or other radar systems, e.g. using electro-magnetic interference [EMI] reduction techniques auxiliary means for detecting or identifying radar signals or the like G01S7/021; means for anti-jamming G01S7/36
• CPC Class Codes: G01S 7/2922 by using a controlled threshold
• CPC Class Codes: G01S 7/2923 based on data belonging to a number of consecutive radar periods

Abstract

A false lock filter circuit for a pulsed altimeter is provided. The circuit includes a low pass filter having a relatively low bandwidth (LBW LPF), a low pass filter having a relatively high bandwidth (HBW LPF) and a false lock controller. The LBW LPF has an input that is coupled to receive a detector output. The HBW LPF has an input that is coupled to receive the detector output. The false lock controller is coupled to receive outputs from the LBW LPF and HBW LPF. Moreover, the false lock controller is configured to sample an output of the HBW LPF and apply a statistical analysis on the samples to determine if a valid target has been detected.

Claims

1. A false lock filter circuit for a pulsed altimeter, the circuit comprising:

a low pass filter having a relatively low bandwidth (LBW LPF) having an input coupled to receive a detector output;

a low pass filter having a relatively high bandwidth (HBW LPF) having an input coupled to receive the detector output; and

a false lock controller coupled to receive outputs from the LBW LPF and HBW LPF, the false lock controller configured to;

sample the outputs of the LBW LPF to detect a first signal above a threshold level;

sample the outputs of the HBW LPF based on the detection of the first signal;

compare HBW LPF samples to a defined signal level to determine the percentage of HBW LPF samples on one side of the defined signal level; and

compare determined percentage with a defined percentage to determine if the first signal is a valid target.

2. The circuit of claim 1, wherein the LBW LPF and the HBW LPF are in a parallel configuration between the detector output and the false lock controller.

3. The circuit of claim 1, wherein the LBW LPF and the HBW LPF are coupled in series with the input of the HBW LPF coupled to the detector output and the output of the HWB LPF coupled to the input of the LBW LPF and a first input to the false lock controller, further an output of LBW LPF coupled to a second input of the false lock controller.

4. The circuit of claim 1, further comprising:

a memory to store thresholds and sample data.

5. The circuit of claim 1, wherein compare the HBW LPF samples to a defined signal level to determine the percentage of HBW LPF samples on one side of the defined signal level includes determine the percentage of samples for a given period that occur above the defined signal level.

6. The circuit of claim 1, wherein compare the HBW LPF samples to a defined signal level to determine the percentage of HBW LPF samples on one side of the defined signal level includes determine the percentage of samples for a given period that occur below the defined signal level.

7. The circuit of claim 1, further comprising:

the false lock controller having an output to provide a target verification signal to a mode controller of the altimeter.

8. An altimeter comprising:

a transmitter to transmit signals;

a detector configured to detect reflected transmit signals;

a false lock filter circuit coupled to an output of the detector, the false lock filter circuit including;

a low pass filter having a relatively low bandwidth (LBW LPF) having an input coupled to receive an output of the detector;

a low pass filter having a relatively high bandwidth (HBW LPF) having an input coupled to receive the output of the detector;

a false lock controller coupled to receive outputs from the LBW LPF and HBW LPF, the false lock controller configured to;

sample outputs of the LBW LPF to detect a first signal above a threshold level;

sample outputs of the HBW LPF based on the detection of the first signal;

compare the HBW LPF samples to a defined signal level to determine the percentage of HBW LPF samples on one side of the defined signal level; and

compare the determined percentage with a defined percentage to determine if the first signal is a valid target; and

a mode control circuit coupled to receive an output of the false lock controller of the false lock filter circuit.

9. The altimeter of claim 8, wherein the false lock filter circuit further comprises:

a memory to store thresholds and sample data.

10. The altimeter of claim 8, wherein the LBW LPF and the HBW LPF of the false lock filter are in a parallel configuration between the detector output and the false lock controller.

11. The altimeter of claim 8, wherein the LBW LPF and the HBW LPF are coupled in series with the HBW LPF being coupled to the output of the detector and to the input of the LBW LPF and to the false lock controller and the LBW LPF being coupled between the HBW LPF and the false lock controller.

12. A method of operating an altimeter system, the method comprising:

monitoring the output of a low pass filter having a relatively low bandwidth (LBW LPF) to detect signals above a noise threshold;

monitoring the output of a low pass filter having a relatively high bandwidth (HBW LPF) to detect signals indicative of a valid target;

sampling the output of the HBW LPF over a period of time based on the signals above the noise threshold;

tracking the signal level at each sample; and

applying statistical analysis to the tracked sample signal levels to determine if a valid target as been detected.

13. The method of claim 12, further comprising:

selecting between a search mode and a tracking mode of the altimeter based on the statistical analysis.

14. The method of claim 12, farther comprising:

transmitting transmit signals from an aircraft;

detecting signals with a detector; and

outputting the detected signals to at least one of the LBW LPF and the HBW LPF.

15. The method of claim 12, further comprising:

setting the noise threshold; and

setting a valid target threshold.

16. The method of claim 15, wherein at least one of the noise threshold and the valid target threshold is based on a standard deviation.

17. The method of claim 15, further comprising:

storing the noise threshold, the valid target threshold and tracked sample signal levels in a memory.

18. The method of claim 12, wherein applying statistical analysis to the tracked sample signal levels to determine if a valid target has been detected, further comprises:

determining the percentage of tracked samples having signal levels more than a valid target threshold;

comparing the determined percentage against a set percentage; and

based on the comparison, determining if a valid target has been detected.

19. The method of claim 12, wherein applying statistical analysis to the tracked sample signal levels to determine if a valid target has been detected further comprises:

determining the percentage of tracked samples having signal levels less than a valid target threshold;

comparing the determined percentage against a set percentage; and

based on the comparison, determining if a valid target signal has been detected.

20. The method of claim 12, further comprising:

verifying the tracking of a valid target periodically by sampling the output of the LBW LPF.