OMNIDIRECTIONAL REFLECTED INTERROGATION REJECTOR

• US 3,715,750 A
• Filed: 07/31/1970
• Issued: 02/06/1973
• Est. Priority Date: 07/31/1970
• Status: Expired due to Term

• Current Assignee: Walton B. Bishop
• Original Assignee: Walton B. Bishop
• Inventors: Bishop, Walton B.
• Primary Examiner(s): Tubbesing, T. H.
• Application Number:
  US05/060,009
• Time in Patent Office: 921 Days
• Field of Search: 343/6.5R,6.5LC,6.8R,6.8LC
• US Class Current: 342/51
• CPC Class Codes: G01S 13/762 with special measures concerning the radiation pattern, e.g. S.L.S. aerials or aerial systems providing at least two radiation patterns, e.g. providing sum and difference patterns, H01Q25/00

Abstract

This application describes a way in which radar-beacon transponders can be made to reject nearly all of the reflected interrogations that reach them without rejecting direct-path interrogations unless two or more interrogators operating on the same interrogation-repetition frequency interrogate a particular transponder simultaneously. Logic circuits are provided to show how the IFF Mark X (SIF), also known as the Air Traffic Control Radar Beacon System (ATCRBS) or the Secondary Surveillance Radar (SSR), can be modified to make use of the new technique. Classified military systems can use it equally well if suitable modifications are made. A circuit is also provided to suppress sidelobe-interrogation decoding instantaneously so that the transponder dead time, no longer needed when reflected interrogations are rejected, can be eliminated.

Claims

1. In a transponder receiving IFF interrogation signals and emitting reply signals, a suppression network for suppressing reply signals to reflected interrogation and sidelobe interrogation comprising:

first means for determining the presence of a sidelobe suppression signal, said first means including delay means for delaying said interrogation signals, first coincidence means for detecting the presence of two pulses spaced 2 microseconds apart in said delaying means, second coincidence means for passing a pulse upon the nonpresence of said two pulse signal;

second means for determining if said interrogation is a reflected main beam interrogation;

third means for determining if said interrogation is a reflected non-main beam interrogation;

an OR gate connected between said second coincidence and said second determining means;

whereby said transponder is suppressed from emitting a reply signal if any of said determining means indicates the presence of a sidelobe or reflected interrogation.

2. A suppression network as recited in claim 1, including:

third coincidence means connected to said second coincidence means and said third determining means whereby said third coincidence means output signal triggers said transponder transmitter and wherein said third determining means supplies a pulse to said third coincidence means only upon determining that said interrogation is not a reflected non-beam interrogation and that said second determining means has supplied an indicating signal that said interrogation is not a reflected main beam interrogation.

3. A suppression network as recited in claim 1 wherein said second determining means comprises:

means for determining the time interval between a second interrogation following a first interrogation within a certain period of time;

means for storing said determined time interval;

means for indicating to said third determining means that no two stored time intervals are identical.