A Compact Broadband Circularly Polarized Antenna with a Backed Cavity for UHF RFID Applications

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Abstract

A compact broadband circularly polarized antenna is designed with a novel method for universal ultra high frequency (UHF) radio frequency identification (RFID) readers. It is composed of a compact ring-shaped patch which aims to decrease the size of the antenna. A quadrature 3 dB coupler placed below the ground plane creates 90° phase differences to generate the circularly polarized radiation of the antenna. To improve the performance of the proposed antenna and minimize its size, we use a coupling feeding method, an FR4 dielectric slab, and a metal cavity. The coupled feeding is implemented to eliminate the mismatching between the long probe and ring-shaped patch, and to improve
the gain over the operating band. The introduction of an FR4 dielectric slab and a cavity can reduce the antenna size and improve the impedance matching and axial ratio (AR) bandwidth. The antenna with a backed cavity can increase the front to back ratio remarkably and improve CP performance further. The measured results show that the antenna with a low profile (0.45λ×0.45λ×0.06λ at 915 MHz) has the impedance bandwidth of 30.2 % (730-990MHz) and 3-dB AR bandwidth of 24.2% (760-970MHz). Both the impedance and the AR bandwidth cover the worldwide UHF RFID band.
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A compact broadband circularly polarized antenna is designed with a novel method for universal ultra high frequency (UHF) radio frequency identification (RFID) readers. It is composed of a compact ring-shaped patch which aims to decrease the size of the antenna. A quadrature 3 dB coupler placed below the ground plane creates 90° phase differences to generate the circularly polarized radiation of the antenna. To improve the performance of the proposed antenna and minimize its size, we use a coupling feeding method, an FR4 dielectric slab, and a metal cavity. The coupled feeding is implemented to eliminate the mismatching between the long probe and ring-shaped patch, and to improve
the gain over the operating band. The introduction of an FR4 dielectric slab and a cavity can reduce the antenna size and improve the impedance matching and axial ratio (AR) bandwidth. The antenna with a backed cavity can increase the front to back ratio remarkably and improve CP performance further. The measured results show that the antenna with a low profile (0.45λ×0.45λ×0.06λ at 915 MHz) has the impedance bandwidth of 30.2 % (730-990MHz) and 3-dB AR bandwidth of 24.2% (760-970MHz). Both the impedance and the AR bandwidth cover the worldwide UHF RFID band.
Original languageEnglish
JournalIET Microwaves, Antennas & Propagation
ISSN1751-8725
Publication statusPublished - Nov 2018
Publication categoryResearch
Peer-reviewedYes
ID: 290392070