Measurement results for multichannel transmit beamforming tag direction detection in passive ultra-high frequency radio-frequency identification systems

As an alternative to classical ultra-high frequency (UHF) radio-frequency identification (RFID) tag localisation methods (e.g. angle of arrival or received signal strength), a new angle-of-activation approach is presented that uses digital multichannel transmit beamforming. By pivoting the main lobe of the interrogator´s transmit antenna array utilising the very sensitive response threshold of passive UHF RFID tags, the tag direction is estimated. The presented three-channel digital beamforming hardware pivots the main lobe of a circularly polarised antenna array in a range of ±52° with an angular resolution of 0.02°. It estimates the direction of a circularly polarised tag with a mean measured accuracy of 0.9° in a basic multipath environment.