Interrogator with variable maximum output power

摘要

A method of reading a plurality of RF transponders (14.1 to 14.15) is disclosed and claimed. The method includes the steps of transmitting a first energizing signal generating a first energizing field having a first range (Pm1), receiving response signals from transponders (14.1 to 14.3) within the range and reading data in the signals. The method further includes the step of causing transponders (14.1 to 14.3) just read to cease responding to the energizing signal. Thereafter a second energizing signal generating a second energizing field having a second range (Pm2) is transmitted. Response signals from remaining transponders (14.4 to 14.8) within the second field are received and read. Thereafter transponders (14.4 to 14.8) are also caused to cease responding, before a third energizing signal intended to read transponders (14.9 to 14.15) is transmitted. An electronic identification system, an interrogator for transponders and a method of searching and finding a selected transponder amongst a plurality of transponders distributed in a volume are also disclosed and claimed.