A Wideband Single-Fed, Circularly-Polarized Patch Antenna With Enhanced Axial Ratio Bandwidth for UHF RFID Reader Applications

A wideband single-fed, circularly-polarized patch antenna with enhanced axial ratio bandwidth for RFID reader application is proposed. The antenna consists of a modified half E-shaped patch, a near-field resonant parasitic (NFRP) patch, and four rotated vertical metallic plates on the ground plane. The metallic plates surrounding the main radiator of the modified half E-shaped patch antenna are fabricated vertically on the ground plane. The operating frequency of the antenna decreases substantially with the vertical metallic plates, which is important for miniaturization of RFID applications. With an elliptical slot and a cut on the modified half E-shaped patch, antenna impedance bandwidth and CP performance both improve. A truncated corner patch as an NFRP element can generate an additional CP radiation mode and further enhances the axial ratio and impedance bandwidth. The measured results show that the antenna has an impedance bandwidth of 14.2% (833-960 MHz), a 3-dB AR bandwidth of 9.0% (846-926 MHz), and an average gain of 7.3 dBic over a 3-dB AR bandwidth. The proposed antenna has a compact size and a low profile (0.45 lambda(0) x 0.45 lambda(0) x 0.074 lambda(0)).