An Eccentric Annular Slotted Patch with Parasitic Element for UHF RFID Reader Applications

In this paper, an eccentric annular slotted patch antenna for ultra-high-frequency (UHF) radio frequency identification (RFID) reader antenna is initially investigated. To easily attain good impedance bandwidth, the proposed radiating patch is mounted on an L-shaped ground (200 mm × 200 mm × 57 mm) and it has a planar size of 170 mm × 170 mm. To further achieve better circular polarized (CP) bandwidth (or 3-dB axial ratio bandwidth), the technique of loading a parasitic arc-shaped element besides the radiating patch is introduced. The measured result has shown that the proposed antenna can yield 10-dB impedance bandwidth of 56.53% (0.618-1.105 GHz), and its corresponding CP bandwidth was improved to 6.13% (0.886-0.942 GHz) due to the parasitic element.