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 readerdetermining maximum operational distance.A prototype reader working at the frequency of 915 MHz 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.