Open AccessCompact broadband circularly‐polarised antenna with a backed cavity for UHF RFID applications
Author(s) -
Li JunLong,
Liu Hui,
Zhang Shuai,
Zhang Yuan,
He Sailing
Publication year - 2019
Publication title -
iet microwaves, antennas and propagation
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.555
H-Index - 69
eISSN - 1751-8733
pISSN - 1751-8725
DOI - 10.1049/iet-map.2018.5321
Subject(s) - microstrip antenna , optics , patch antenna , ground plane , impedance matching , ultra high frequency , materials science , monopole antenna , broadband , axial ratio , bandwidth (computing) , antenna tuner , antenna measurement , coaxial antenna , optoelectronics , electrical impedance , physics , antenna (radio) , microstrip , electrical engineering , telecommunications , engineering , circular polarization
A compact broadband circularly‐polarised (CP) 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 CP radiation of the antenna. To improve the performance of the proposed antenna and minimise its size, the authors 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 the 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 the CP performance further. The measured results show that the antenna with a low profile (0.45 λ 0 × 0.45 λ 0 × 0.06 λ 0 at 915 MHz) has the impedance bandwidth of 30.2% (730–990 MHz) and 3 dB AR bandwidth of 24.2% (760–970 MHz). Both the impedance and the AR bandwidth cover the worldwide UHF RFID band.