Method for detecting RFID transponders and transponder reader system

摘要

A method for energising and detecting RFID transponders in which a phase relationship between first and second power signals used to power first and second parts (34, 36) of an antenna (24) is repeatedly switched to produce two different field patterns. The regions which may allow transponders having a certain orientation to escape detection may be different for each phase relationship. By selecting the phase relationships appropriately and performing the phase switching at a rate to ensure that any transponder travelling through the antenna range is exposed to each field pattern, the probability of a transponder escaping detection can be reduced.