Signal descriptions and formulations for long range UHF RFID readers

In this paper, signal descriptions and formulations for the radio frequency ( RF) front-end of a passive backscatter radio frequency identification ( RFID) reader working at ultra high frequencies ( UHF) are discussed in detail, and a set of design considerations aiming to improve the read range are outlined. The reader's architecture is proposed and the design details of its RF frond-end are presented. The read range is formulated through calculating the time-averaging power absorbed by the tag and the signal-noise-ratio ( SNR) of the demodulation, and accordingly RFID systems can be classified into tag-determining and reader-determining ones. It is concluded that the gain of the reader antenna, the phase noise of the local oscillation ( LO) and the receive-transmit isolation coefficient dominate the demodulation output noise of the reader, and consequently the reader-determining maximum operational distance. A prototype reader working at the frequency of 915MHz was built with off-the-shelf components and was evaluated with a commercial tag in an indoor environment. The measured results show that this RFID system is of tag-determining and has a read range of 8.4 meters, which are in good agreement with the calculated results.