A system design for the reader of microwave radio frequency identification

RFID (Radio Frequency Identification) is now attracting many interests for its bright future in commercial and daily use. For the low-frequency (LF, typically 125KHz) and the high-frequency (HF, typically 13.6MHz) RFIDs, the Readers have already come into our daily life out of their matured technologies, while the ultra-high frequency (UHF) RFID Readers are still in the process for the reliability and functionality. This paper represents a systematic design of a UHF RFID reader. Received backscatter modulation waves (carrier wave frequency 915 MHz) are directly demodulated to baseband signals using the Zero IF technology. The reader is designed as a quadrature (I/Q) one, which can avoid null points of the received signals [41 and enhance the demodulation sensitivity.