Device for protecting SSR transponders against unintended triggering on an airport with very limited muting activity in vertical direction
First Claim
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.
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Accused Products
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.
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Citations
9 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.
- 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.
- 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.
Specification