GEOGRAPHIC ADDRESSING BY INTERROGATION FOR CONTROLLING AIRPORT GROUND TRAFFIC

摘要

The geographical location of on-the-ground traffic having on-board ATC transponders can be specifically addressed through the use of two spaced apart interrogators. A first interrogator transmits a first message at least over a field of interest except that a message null exists in a narrow beam. Transponders within the field of interest but outside the null beam are suppressed for a predetermined period of time while transponders within the null beam are not suppressed. A second interrogation subsequently transmits an interrogation along a second narrow beam. Only a transponder located within the geographical area defined by the intersection of the two beams are not suppressed and also illuminated by the interrogation and hence only that transponder responds.