System for and method of locating radio frequency identification (RFID) tags associated with items in a controlled area

摘要

A radio frequency identification (RFID) tag reading system having a phased antenna array accurately locates RFID tags in a controlled area, by steering an interrogating beam over the controlled area to interrogate the tags and generate return modulated RF signals. A primary receiver steers a primary receive beam at a primary steering angle that is fixed during each tag interrogation. A primary demodulator demodulates and reconstructs the received return modulated signals. A secondary receiver, independently of the primary receiver, steers a secondary receive beam at a plurality of secondary steering angles. A secondary correlator/demodulator demodulates the combined return modulated signals, and utilizes the reconstructed signal reconstructed by the primary demodulator at each of the secondary steering angles. Both the primary and the secondary receivers cooperate to accurately locate the same tag.

主权项

1. A radio frequency (RF) identification (RFID) tag reading system for accurately locating RFID tags associated with items in a controlled area, comprising:
a phased antenna array; an RF transmitter for steering an interrogating beam over the controlled area to interrogate the tags and generate return modulated RF signals from the tags by transmitting an RF interrogating signal over the phased antenna array to generate the interrogating beam; a primary RF receiver for steering a primary receive beam over the controlled area at a primary steering angle that is fixed during each tag interrogation, and for detecting the tags by receiving and combining the return modulated RF signals as the primary receive beam over the phased antenna array, the primary RF receiver including a primary demodulator for demodulating combined return modulated RF signals from the primary RF receiver to detect each tag, for reconstructing received return modulated RF signal for each tag, and for measuring a primary received signal strength for each tag; and a secondary RF receiver operative, independently of the primary RF receiver, for steering a secondary receive beam over the controlled area at a plurality of secondary steering angles by receiving and combining the return modulated RF signals as the secondary receive beam over the phased antenna array, the secondary RF receiver including a secondary demodulator for demodulating combined return modulated RF signals from the secondary RF receiver to generate a demodulated RF signal from the secondary RF receiver, and for measuring a secondary received signal strength utilizing both the demodulated RF signal from the secondary RF receiver and reconstructed tag signal reconstructed by the primary demodulator at each of the secondary steering angles, whereby both the primary and the secondary RF receivers cooperate to accurately locate same tag even if the secondary received signal strength is below a threshold value.