Demonstration of improved passive UHF RFID coverage using optically-fed distributed multi-antenna system

Optically-fed distributed antenna system (DAS) technology is combined with passive ultra high frequency (UHF) radio frequency identification (RFID). It is shown that RFID signals can be carried on directly modulated radio over fiber links without impacting their performance. It is also shown that a multi-antenna DAS can greatly reduce the number of nulls experienced by RFID in a complex radio environment, increasing the likelihood of successful tag detection. Consequently, optimization of the DAS reduces nulls further. We demonstrate RFID tag reading using a three antenna DAS system over a 20 m times 6 m area, limited by building constraints, where 100% of the test points can be successfully read. The detected signal strength from the tag is also observed to increase by an average of approximately 10 dB compared with a conventional switched multi-antenna RFID system. This improvement is achieved at +31 dBm equivalent isotropically radiated power (EIRP) from all three antenna units (AUs).