A slotted circularly-polarized patch antenna for near-field and far-field UHF RFID applications

Abstract

A slotted patch antenna is proposed for near-field and far-field ultra high frequency (UHF) radio frequency identification (RFID) applications. By slotting the patch, the antenna is able to produce strong and uniform magnetic field in the near field and generate the circularly-polarized radiation in the far field. The fabricated antenna (90 mm × 90 mm × 4.5 mm) with 10-dB return loss and 3-dBic gain from 913 MHz to 924 MHz, achieves a 100% reading rate for arbitrary oriented near-field tag over a distance of 35 mm and offers a far-field tag reading up to 3.6 m. The antenna is suitable for portable near-field and far-field UHF RFID readers.