Method for controlling the angular extent of interrogation zones in RFID

A new broadcasting method for radio frequency identification (RFID) controls the reader's interrogation zone by using a two-element antenna to transmit a data signal with a directional sum pattern and a scramble signal with a complementary difference pattern. Only the data signal communicates with RFID tags, and the beam patterns are chosen so that the scramble signal dominates the data signal except in one angular sector. Simulations and experiments with a commercial reader and off-the-shelf RF components show that this method can create a narrow, adjustable interrogation zone for identifying and locating tags, even in complex indoor environments.