Air traffic control radar beacon system multipath reduction apparatus and method

• US 4,970,518 A
• Filed: 12/07/1988
• Issued: 11/13/1990
• Est. Priority Date: 12/07/1988
• Status: Expired due to Fees

• Current Assignee: Northrop Grumman Corporation
• Original Assignee: Westinghouse Electric Corporation (Paramount Global (f/k/a ViacomCBS Inc.))
• Inventors: Cole, Elbert L. Jr.
• Primary Examiner(s): Tarcza, Thomas H.
• Assistant Examiner(s): Sotomayor, John B.
• Application Number:
  US07/280,910
• Time in Patent Office: 706 Days
• Field of Search: 342/36-40, 342/32
• US Class Current: 342/37
• CPC Class Codes: G01S 13/784 Coders or decoders therefor; Degarbling systems; Defruiting systems

Abstract

A system and method for detecting and removing specular multipath reports from terminal ATCRB systems for aircraft targets having Mode 3/A transponder reporting capabilities. Reports are delayed for a first time, or azimuth, interval to determine whether the report is multipath or to identify future occurrences of multipath reports. After the first azimuth interval, the report is released for display and a fragment of the report is retained for an additional azimuth interval. Of two reports with matching Mode 3/A code, the one with the greater range is considered to be a multipath reply. If the multipath report range falls within a multipath range interval and has not been released for display, it is discarded by the system as an erroneous report.

Claims

1. A method of eliminating specular multipath target reports from an air traffic control system radar displaying azimuth, range, and target identification, comprising the steps of:

storing received radar reports for first and second portions of a predetermined time interval corresponding to first and second angles in azimuth;

detecting successive reports corresponding to stored reports having the same target identification;

comparing the range of each detected report with the corresponding stored report;

eliminating the report having the greater range at times when a detected successive report and the corresponding stored report are both received in the first portion of the predetermined time interval and the difference between the ranges of the successive detected report and the corresponding stored report is less than a predetermined value;

eliminating the successive detected report at times when the successive detected report and the corresponding stored report are both received within the second portion of the predetermined time interval and the range of the successive detected report is greater than the range of the corresponding stored report; and

displaying the stored reports not eliminated by the eliminating step.

2. An apparatus for eliminating specular multipath target reports from an air traffic control radar system displaying azimuth, range, and target identification, comprising:

means for storing received radar reports for first and second portions of a predetermined time interval corresponding to first and second angles in azimuth;

means for detecting successive reports corresponding to stored reports having the same target identification;

means for comparing the range of each detected report with the corresponding stored report;

means for eliminating the report having the greater range at times when a detected successive report and the corresponding stored report are both received in the first portion of a predetermined time interval and the difference between the ranges of the successive detected report and the corresponding stored report is less than a predetermined value;

means for eliminating the successive detected report at times when the successive detected report and the corresponding stored report are both received within the second portion of the predetermined time interval and the range of the successive detected report is greater than the range of the corresponding stored report; and

means for displaying the stored reports not eliminated by the eliminating means.

3. An apparatus for eliminating specular multipath aircraft reports from an airport terminal air traffic control radar beacon system which provides range, azimuth, and transponder code reports of aircraft, said apparatus comprising:

delay memory means for storing a plurality of reports from the radar system;

control means having multipath range intervals, a first azimuth interval and a second azimuth interval, for directing said delay memory means to output each of said reports remaining in said delay memory means to a report monitoring system when said each report has been stored for a duration equal to said first azimuth interval and for discarding said each report when said each report has been stored for a duration equal to said second azimuth interval;

code matching means for comparing each of the reports in said delay memory means to the most recently received one of the reports, called a latest report, and for providing a code match signal when the code in said latest report matches the code of one of said stored reports, called a prior report; and

inspection means, responsive to said code matching means and said control means, for directing said delay memory means to discard said latest report when the range of said latest report, called the latest range, is greater than the range of said prior report, called the prior range, at times when the difference between said latest and prior ranges is less than or equal to a selected one of said multipath range intervals, and when the difference between the azimuth of said latest report, called the latest azimuth, and the azimuth of said prior report, called the prior azimuth, is less than or equal to said first azimuth interval, and for directing said delay memory means to discard said prior report when said latest range is less than said prior range, at times when the difference between said latest and prior ranges is less than or equal to a selected one of said multipath range intervals, and when the difference between said latest azimuth and said prior azimuth is less than or equal to said first azimuth interval.

4. The apparatus of claim 3 wherein said control means includes means for specifying code match parameters to said code matching means.

5. The apparatus of claim 4 wherein said code match parameter directs said code matching means to match Mode 3/A transponder codes.

6. The apparatus of claim 4 wherein said code match parameter directs said code matching means to match non-discrete transponder modes.

7. The apparatus of claim 4 further including a window memory, coupled between said control means and said inspection means, for storing and providing to said inspection means, said multipath range intervals, said first azimuth interval, and said second azimuth interval.

8. The apparatus of claim 3 wherein said delay memory means stores only a portion of said reports during the period of said second azimuth interval following said first azimuth interval.

9. The apparatus of claim 3 further comprising means for enabling the elimination of specular multipath aircraft reports when said radar beacon system is pointing in directions known to cause multipath reports and for disabling the elimination of specular multipath aircraft reports when said radar beacon system is pointing in directions known to be free of multipath reports.

10. A method for eliminating specular multipath aircraft reports from an airport terminal air traffic control radar beacon system which provides range, azimuth, and transponder code reports of aircraft, comprising the steps of:

storing a plurality of reports from the radar system in a delay memory means;

controlling said delay memory means to output each of said reports remaining in said delay memory means to a report monitoring system when said each report has been stored for a duration equal to a first azimuth interval and for discarding said each report when said each report has been stored for a duration equal to a second azimuth interval;

comparing each of the reports in said delay memory means to the most recently received one of the reports, called a latest report, and for providing a code match signal when the code in said latest report matches the code of a matching one of said stored reports, called a prior report; and

directing said delay memory means to discard said latest report when the range of said latest report, called the latest range, is greater than the range of said prior report, called the prior range, when the difference between said latest and prior ranges is less than or equal to a selected multipath range interval, and when the difference between the azimuth of said latest report, called the latest azimuth, and the azimuth of said prior report, called the prior azimuth, is less than or equal to said first azimuth interval, and for directing said delay memory means to discard said prior report when said latest range is less than said prior range, when the difference between said latest and prior ranges is less than or equal to a selected multipath range interval, and when the difference between said latest azimuth and said prior azimuth is less than or equal to said first azimuth interval.

11. The method of claim 10 wherein said step of comparing includes matching Mode 3/A transponder codes.

12. The method of claim 10 wherein said step of comparing includes matching non-discrete transponder modes.

13. The method of claim 10 wherein said step of storing includes storing only a portion of said reports during the period of said second azimuth interval following said first azimuth interval.

14. The method of claim 10 further comprising a step of enabling the elimination of specular multipath aircraft reports when said radar beacon system is pointing in directions known to cause multipath reports and disabling the elimination of specular multipath aircraft reports when said radar beacon system is pointing in directions known to be free of multipath reports.