A novel RX-TX front-ends for passive RFID reader with high isolation

In passive radio frequency identification (RFID) system, the isolation between transmitter and receiver has been a critical problem because the TX and RX are simultaneous. A directional coupler has been used to isolate RX from TX, whereas some latent disadvantage of insertion loss of receiver signal and poor isolation have already emerged from conventional microstrip directional coupler because of low coupling and unequal phase velocity between even and odd mode. In this paper, a new RX-TX Front-Ends based on a 3dB branch-line coupler is proposed to reduce the insertion loss of the received signal and improve the isolation by Reflected Power Canceller (RPC) between TX and RX. The results of the proposed method show that the insertion loss of received signal is about 3dB and the transmit/receive isolation is more than 46dB in the UHF RFID frequency band.