Novel Broadband Center-Fed UHF Near-Field RFID Reader Antenna

A broadband center-fed ultra-high frequency (UHF) near-field radio frequency identification (RFID) reader antenna is proposed and investigated in this letter. The design utilizes four tapered double-side parallel stripline (TDSPSL)-fed dipoles to form a circular loop to achieve broadband impedance matching and strong and uniform magnetic field distribution. Parametric studies are carried out to characterize the design concept. The proposed antenna was fabricated and measured. The measured 10-dB impedance bandwidth is 236 MHz (814-1050 MHz), which covers the entire UHF RFID frequency band. The maximum reading distance is 210 mm at 30 dBm input power. Moreover the antenna can achieve a 100% read percentage within the height of 135 mm for multitag detection. The measured results agree well with the simulated ones.