Radio link analysis and design of directional coupler with high isolation for UHF RFID reader

The radio link between reader and tag for UHF band RFID is discussed and analyzed, focusing in particular on minimum transmitting power and improving the sensitivity of the receiver in order to emphasis on the necessity of increasing the isolation between TX and RX for high performance of reader; based on the conventional microstrip directional coupler, a method is introduced to achieve high isolation and good direction. The experimental results show the improved coupling can achieve high performance with the isolation of 58.875 dB and directivity of 45 dB at 915 MHz, and suppress carrier leakage into receiver channel effectively, which is able to satisfy the requirement of the isolation of UHF reader with 902-928 MHz.