Circularly polarized antenna with circular shaped patch and strip for worldwide UHF RFID applications

A circularly polarized Radio Frequency Identification (RFID) reader antenna is proposed for worldwide Ultra-High Frequency (UHF) (840-960 MHz) applications. The antenna is composed of two circular shaped patches, a ring shaped strip, and a suspended conducting strip with open-circuited termination. The simulations show that the antenna has an impedance bandwidth (S11 <; -25 dB) of about 17.4% (807-961 MHz), 3-dB axial ratio (AR) bandwidth of about 14.4% (833-962 MHz), 2-dB AR bandwidth of 12.9% or 842-958 MHz, and gain level of about 9.1 dBic or larger within the 3-dB AR bandwidth. The proposed antenna can be a good candidate for universal UHF RFID readers at the UHF band of 840-960 MHz, which has excellent impedance matching (S11 <; -25 dB), high gain (Gain > 9.1 dBic), and good AR (AR<; 2 dB) performance.