Device for protecting SSR transponders against unintended triggering on an airport with very limited muting activity in vertical direction

• US 5,623,268 A
• Filed: 10/06/1994
• Issued: 04/22/1997
• Est. Priority Date: 10/06/1994
• Status: Expired due to Fees

• Current Assignee: British Technology Group Ltd.
• Original Assignee: British Technology Group Ltd.
• Inventors: De Haan, Frans H.
• Primary Examiner(s): Lobo, Ian J.
• Application Number:
  US08/319,019
• Time in Patent Office: 929 Days
• Field of Search: 342/30, 342/32, 342/37, 342/463, 342/464
• US Class Current: 342/32
• CPC Class Codes: G01S 13/784 Coders or decoders therefor; Degarbling systems; Defruiting systems
• CPC Class Codes: G01S 13/934 on airport surfaces, e.g. while taxiing
• CPC Class Codes: G01S 2013/466 by Trilateration, i.e. two antennas or two sensors determine separately the distance to a target, whereby with the knowledge of the baseline length, i.e. the distance between the antennas or sensors, the position data of the target is determined

Abstract

A device is provided for interrogating airborne SSR transponders at an airport, in which in certain regions which are made non-active, P1 pulses are transmitted followed, with the correct timing, by P2 pulses which have the same or a larger amplitude than the P1 pulses. As a consequence, SSR transponders in these regions are blocked or muted, and this blocking or muting is repeated, whereas in one or a few selected regions, normal interrogating signals are transmitted. Spreading of transmitted pulses to higher levels above ground is countered by keeping the energy of the pulses low and the vertical gain of transmitter antennas small.

Claims

1. A system for localizing SSR transponders at an airport, said system comprising a plurality of transmitters for transmitting an interrogation signal, a plurality of receivers for receiving a response signal of an SSR transponder in response to said interrogation signal, the airport being divided in a plurality of divisional regions, and said transmitters transmitting interrogating signals suitable to cause an SSR transponder present in a predetermined divisional region to respond, means for controlling said transmitters such that transmitters interrogating different divisional regions transmit, successively, pulses which, in different divisional regions are received as interrogating signals P1, P3, said interrogating signals comprising a first pulse P1, a second pulse P2 of smaller reception strength than the first pulse and transmitted after a first predetermined time period and a third pulse P3 transmitted a second predetermined period after the time allotted to the second pulse, said SSR transponders being muted during a time period longer than the sum of said first and second periods after reception of a second pulse of a strength at least equal to the first pulse, means for providing transmission into at least one temporary inactive divisional region, spaced from an active divisional region or regions, of, successively, a first pulse P1 having in said at least one temporary inactive divisional region, a first strength and, after said first predetermined period, a second pulse P2 having, in said at least one temporary inactive region, a second strength at least equal to said first strength, said transmission being repeated at intervals of a duration less than the sum of said predetermined first period and said predetermined second period.

2. A system according to claim 1, wherein, between the inactive and the active divisional regions, at least one neutral divisional regions is located in which no interrogating pulses are transmitted.

3. A system according to claim 1 wherein said transmitters each include an antenna having a vertical gain and a horizontal gain which is at least three times greater than said vertical gain.

4. A system as claimed in claim 3 wherein the maximum distance from a transmitter that a SSR transponder can be triggered is less than 500m.

5. A device for determining the locations of SSR transponders on the surface of an airport wherein P1 and P3 interrogating pulses are transmitted by SSR interrogators, said device comprising protective means for protecting transponders from responding to unwanted interrogations by SSR interrogators other than a wanted SSR interrogator, said protective means including means for transmitting into regions, not currently being interrogated by the wanted SSR interrogator, a pulse group comprising a first pulse P1 followed, after a predetermined period, by a second pulse P2 of at least equal amplitude to said pulse P1, said pulse group being repeated at an interval of less than the interval between said interrogation pulses P1 and P3 of the shortest interrogation mode of SSR interrogators used in the region or regions concerned.

6. A system as claimed in claim 5 wherein said transmitters each include an antenna having a vertical gain and a horizontal gain which is at least three times greater than the vertical gain, said transmitters producing a transmission having a strength insufficient to either trigger or mute SSR transponders at ground level at a horizontal distance of more than 500m.

7. A surveying system for an airport provided with interrogating transmitters producing SSR transponder interrogation signals in selected portions of the airport area, wherein said airport is divided into at least ten divisional regions and said regions are provided with muting transmitters for SSR transponders, said surveying system including control means for controlling said muting transmitters so as to cause occurrence of effective muting signals comprising a first pulse P1 and, after a time delay, a second pulse P2, in a plurality of said divisional regions forming an inactive area, without causing the occurrence of said muting signals in other divisional regions outside of said inactive area, said second pulse P2 being at least equal in strength to said first pulse P1.

8. A surveying system according to claim 7, wherein the divisional regions include receiving means for receiving SSR transponder response signals in order to localize the SSR transponder by trilateration.

9. A surveying system according to claim 8, wherein said control means causes a plurality of said divisional regions to be active to mute SSR transponders, one or more divisional regions to be active to carry out trilateration and between one or more divisional regions, the transmitter or transmitters to be inactive.