ANovelRX-TXFront-Ends forPassive RFIDReaderwithHigh Isolation

Inpassive radiofrequency identification (RFID) system, theisolation between transmitter and receiver hasbeena critical problem because theTXand RX are simultaneous. A directional coupler hasbeen usedto isolateRX fromTX,whereas some latent disadvantage ofinsertion lossofreceiversignal and poorisolation havealready emerged fromconventional microstrip directional coupler because oflowcoupling andunequal phase velocity between even andoddmode. Inthispaper,a new RX-TXFront-Ends based on a 3dB branch-line coupler is proposed to reducethe insertion lossofthereceived signal andimprove the isolation byReflected PowerCanceller (RPC) between TXandRX.Theresults oftheproposed method showthat theinsertion lossofreceived signal isabout3dBand thetransmit/receive isolation ismore than46dBinthe UHFRFIDfrequency band. IndexTerms:Isolation, RFID,Coupler