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International Journal of Antennas and Propagation
Volume 2013 (2013), Article ID 349817, 10 pages
Research Article

Circularly Polarized Low-Profile Antenna for Radiating Parallel to Ground Plane for RFID Reader Applications

1Faculty of Engineering, King Mongkut’s Institute of Technology Ladkrabang, Chalongkrung Road, Ladkrabang, Bangkok 10520, Thailand
2Graduate School of Science and Technology, Kumamoto University, 2-39-1 Kurokami, Chuo-ku, Kumamoto 860-8555, Japan

Received 4 September 2013; Revised 4 October 2013; Accepted 5 October 2013

Academic Editor: Z. N. Chen

Copyright © 2013 Kittima Lertsakwimarn et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.


This paper presents a low-profile printed antenna with double U-shaped arms radiating circular polarization for the UHF RFID readers. The proposed antenna consists of double U-shaped strip structures and a capacitive feeding line to generate circular polarization. A part of the U-shaped arms is bent by 90° to direct the main beam parallel to the ground plane. From the results, 10 dB and 3 dB axial ratio of the antenna cover a typical UHF RFID band from 920 MHz to 925 MHz. The bidirectional beam is obtained with the maximum gain of 1.8 dBic in the parallel direction to the ground plane at the 925 MHz. The overall size of the proposed antenna including ground plane is 107 mm × 57 mm × 12.8 mm (0.33 × 0.17 × 0.04 ).