Multiple-Arm Dipoles Reader Antenna for UHF RFID Near-Field Applications

A multiple-arm dipoles antenna array based on magnetic coupling is proposed for ultrahigh frequency (UHF) radio frequency identification (RFID) near-field application. The design utilizes four multiple-arm dipoles to form a square region fed by a quarter-wave impedance transformer double-side parallel stripline (QDSPSL) structure. Broadband performance can be obtained for two different resonant frequencies caused by different dipole arm lengths. Moreover, in induction area, stronger and more uniform magnetic field distribution is generated for phases of currents on three dipole arms being kept in the same compared to conventional single-arm dipole. A 170 x 170 x 1.6 mm(3) antenna has been fabricated on an FR-4 substrate to fit RFID near-field application. The measured 10-dB impedance bandwidth is 190 MHz (810-1000 MHz), which covers the entire UHF RFID frequency band (860-960 MHz). Measured tests on the antenna read range are carried out, exhibiting a reading region of 100 x 100 mm(2) and 100% reading rate within 200 mm for near-field tags.