Circularly Polarized Stacked Annular-Ring Microstrip Antenna With Integrated Feeding Network for UHF RFID Readers

• Published in: IEEE antennas and wireless propagation letters Vol. 9; pp. 542 - 545
• Main Authors: Chen, Xi, Fu, Guang, Gong, Shu-Xi, Yan, Ya-Li, Zhao, Wei
• Format: Journal Article
• Language: English
• Published: New York IEEE 2010; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Annular-ring; Antenna feeds; axial ratio (AR); Bandwidth; circularly polarized (CP); feeding network; Frequency; Impedance matching; microstrip antenna; Microstrip antennas; Polarization; Power dividers; Radiofrequency identification; Shape; UHF antennas
• ISSN: 1536-1225; 1548-5757
• DOI: 10.1109/LAWP.2010.2051791

A novel circularly polarized (CP) annular-ring microstrip antenna (ARMSA) is proposed for American ultrahigh frequency (UHF) radio frequency identification (RFID) readers. The annular ring is fed by an equal-split power divider with 90° phase difference. For the compactness of the entire antenna, the divider with the shape of Archimedes gradual-change lines is designed at the inside of the annular ring. A circular parasitic patch is suspended above the ring to improve the impedance matching and bandwidth. It also enhances the performances of axial ratio (AR). The impedance bandwidth for S 11 <; -10 dB and 3-dB AR bandwidth are 870-967 MHz (10.6% at 915 MHz) and 893-948 MHz (6%), respectively. The CP gain is 8.9 dBi at 915 MHz with the front-to-back ratio (F/B) of 16.5 dB. The proposed antenna is low profile as the total height is 0.043 λ 0 (λ 0 is the free-space wavelength).