Multifeed tri-band circularly polarized antenna for UHF/MW-RFID application

A compact three-port tri-band circularly polarized (CP) antenna for radio-frequency identification (RFID) technique is introduced. Four inverted-F radiating elements fed with a 90 degrees phase delay feeding network realize the CP radiation at the FCC UHF-RFID band (0.902-0.928 GHz). With the slot-coupled feeding technique, Corner-truncated slot and patch have been employed to achieve CP radiation at MW-RFID bands (2.4-2.485/5.725-5.875 GHz). Decoupling structures are implemented to obtain excellent 20 dB port isolations during all operating bands. The relative impedance bandwidths in the three bands are 6.6%, 5.3%, and 5.1%, respectively, with peak gains of 2, 5.1, and 5.7 dBic.