All-Metal High-Efficiency Wideband Circularly Polarized Patch Antenna

A modified version of the circularly polarized (CP) U-slot patch antenna is proposed in this paper. This design added a vertical metal sheet to the center of the U-shaped slot, which serves as a capacitor between the patch and the ground plane. This capacitor solved one problem of previous research, that is: an all-metal structure cannot coexist with large CP bandwidth that has two zeros in its axial-ratio (AR)-frequency response. It achieved this by lowering the resonance frequency of one of the characteristic modes of the patch. Based on this structure, an antenna for the application of UHF RFID reader is designed, fabricated, and measured. Measured results show a −10dB impedance bandwidth of 19.0%, 3dB AR bandwidth of around 16.3%, and peak realized gain of 8.1 dBic.