US4899156A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Virtual ATCRBS using signals of remote SSR
Assignee: Litchstreet Co
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Filing: 1989-07-13
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Granted: 1990-02-06
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Expires: 2009-07-13
Abstract
Abstract A virtual secondary surveillance radar (SSR) of the type described in U.S. Pat. No. 4,115,771 can produce inaccurate or indeterminate range information for a transponder positioned near or on a line between the actual SSR and the virtual SSR, owing to unfavorable geometrical relationships. When such condition occurs, the error or ambiquity is resolved by transmitting interrogations from the virtual SSR site toward the actual SSR. The time delay between transmission of an interrogation and reception of a reply to it is a direct measure of the range of the transponder from the virtual SSR.
Inventors
- 👤 George B. Litchford
- 👤 Burton L. Hulland
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-11-01 18:21
CPC Classifications
G; G01; G01S; G01S13/00; G01S13/74; G01S13/76; G01S13/78; G01S13/781; G01S13/87; G01S5/00; G01S5/02; G01S5/06
Claims Analysis
Total Claims: 18
Claim 1
Independent Claim
140 words
In a system for indicating the position of a transponder with respect to a reference position at a known location within the service area of a secondary surveillance radar (SSR) by receiving at said location interrogations from said SSR and replies from the transponder and determining the position of the transponder from the time relationships between said received interrogations and replies, the improvement comprising, at said reference position: (a) an antenna; (b) active range measuring transmitter-receiver means coupled to said antenna; (c) means for providing a control output in response to the presence of the transponder in an area on or close to a line between the reference position and the SSR which is geometrically unfavorable to passive determination of its range; and (d) means responsive to said control output to actuate said active range measuring means briefly and intermittently.
Claim 2
Dependent Claim
140 words
In a system for indicating the position of a transponder with respect to a reference position at a known location within the service area of a secondary surveillance radar (SSR) by receiving at said location interrogations from said SSR and replies from the transponder and determining the position of the transponder from the time relationships between said received interrogations and replies, the improvement comprising, at said reference position: (a) an antenna; (b) active range measuring transmitter-receiver means coupled to said antenna; (c) means for providing a control output in response to the presence of the transponder in an area on or close to a line between the reference position and the SSR which is geometrically unfavorable to passive determination of its range; and (d) means responsive to said control output to actuate said active range measuring means briefly and intermittently.
Claim 3
Dependent Claim
27 words
The system of claim 1, wherein said antenna a is directive, pointed at said SSR, and is also coupled to means for receiving interrogations from said SSR.
Claim 4
Dependent Claim
39 words
The system of claim 1, wherein said means c for providing a control output includes comparator means for producing an output in response to a decrease in the differential time of arrival t below a predetermined value min .
Claim 5
Dependent Claim
47 words
The system of claim 3, wherein said means c further includes a second comparator means for producing an output in response to a decrease in the difference in bearing of the transponder from that of the SSR, as viewed from the reference position, below a predetermined value.
Claim 6
Dependent Claim
29 words
The system of claim 4, wherein said means c further includes means for inhibiting a control signal output in the absence of output from either of said comparator means.
Claim 7
Dependent Claim
38 words
The system of claim 2, further including means for alternately pointing the beam axis of said antenna several degrees first to one side and then to the other of the line between said reference position and the SSR.
Claim 8
Dependent Claim
16 words
The system of claim 1, wherein said active range measuring means includes reply pulse degarbling equipment.
Claim 9
Dependent Claim
23 words
The apparatus of claim 1, further including means for varying the transmitter power level of said active range measuring means in successive interrogations.
Claim 10
Independent Claim
128 words
A method of determining the position of a transponder with respect to a reference position at a known location within the service area of a secondary survillance radar (SSR) by receiving at said location interrogations from said SSR and replies from the transponder and determining the position of the transponder from the time relationships between said received interrogations and replies, further including the steps of (a) sensing from said time relationships the presence of a transponder in an area on or close to a line between the reference position and the SSR which is geometrically unfavorable to passive determination of its range, and (b) transmitting interrogations from and receiving replies at said reference position for active measurement of the range of such transponder in response to said sensing.
Claim 11
Independent Claim
128 words
A method of determining the position of a transponder with respect to a reference position at a known location within the service area of a secondary survillance radar (SSR) by receiving at said location interrogations from said SSR and replies from the transponder and determining the position of the transponder from the time relationships between said received interrogations and replies, further including the steps of (a) sensing from said time relationships the presence of a transponder in an area on or close to a line between the reference position and the SSR which is geometrically unfavorable to passive determination of its range, and (b) transmitting interrogations from and receiving replies at said reference position for active measurement of the range of such transponder in response to said sensing.
Claim 12
Dependent Claim
19 words
The method of claim 9, wherein said step b is performed in a directive pattern pointed toward the SSR.
Claim 13
Dependent Claim
25 words
The method of claim 9, wherein step a includes sensing a decrease of differential time of arrival t below a predetermined value t min .
Claim 14
Dependent Claim
33 words
The method of claim 11, further including sensing a decrease in the difference in bearing of the transponder from that of the SSR, as viewed from the reference position, below a predetermined value.
Claim 15
Dependent Claim
32 words
The method of claim 12, further including the step of inhibiting transmission of interrogations from said reference position in the absence of concurrent sensing of both said decreases below said predetermined values.
Claim 16
Dependent Claim
32 words
The method of claim 13, further including the step of inhibiting transmission of said interrogations when the SSR beam is pointing within a sector that includes the location of the virtual SSR.
Claim 17
Dependent Claim
25 words
The method of claim 13, further including the step of inhibiting said interrogations during an interval of 1000 to 1500 microseconds following each P3 pulse.
Claim 18
Dependent Claim
17 words
The method of claim 15, further including the step of randomly varying the length of said interval.
References Cited (Backward Citations)
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Cited
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USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1993-02-05 | 1993-08-07 | 1994-02-06 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1997-02-05 | 1997-08-07 | 1998-02-06 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 2001-02-05 | 2001-08-07 | 2002-02-06 | $7700.00 | Window Closed / Lapsed |