A low-profile circularly polarized (CP) antenna for a handheld Ultra-High Frequency Radio Frequency Identification (UHF RFID) reader is proposed in this paper. The radiating part on the top substrate is composed of three inverted-F elements rotated 120˚ around the center of the structure. A power splitting circuit, placed on the bottom substrate, based on a series transmission line feed delivers equal amplitude to the three IFA with a sequential 120˚ phase shift. Both layers are fabricated on low-cost FR4 material. This design has a disk form factor with a compact size of 35 mm circle radius and an 8.6 mm height. The measurement shows good results with S11 as lower than -10 dB for the whole band, 3 dB-axial ratio around 110˚ (10 MHz of bandwidth), directivity reaching 4.4 dBic, and the total gain of the antenna is 1.9 dBic. In order to validate the proposed antenna performance, a UHF RFID handheld reader is built based on the ThingMagic M6E-Nano module. Different scenarios are investigated to validate the proposed antenna performance in a real environment.
"Miniature Circularly Polarized Antenna for UHF RFID Handheld Reader: Design and Experiments," Progress In Electromagnetics Research M,
Vol. 93, 43-52, 2020. doi:10.2528/PIERM20041004
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