A single port dipole for UHF RFID tag antennas with eliminated read-orientation sensitivity

In this paper, a passive UHF RFID tag antenna of planar circular-loop single port dipole is designed. The alteration of external circular-loop geometrical parameters can eliminate the read-orientation sensitivity of the tag antenna with ease. An inductively coupled feed method was adopted to facilitate impedance matching of the proposed antenna. The measured results are in good agreement with the simulated ones. It showed that the tag possesses the normalized gain deviation of less than 2.5 dB in E and H planes at the frequency of 915 MHz. The measured maximum reading range between the tag and the reader falls in 2.4 m ∼ 2.9 m, depending on the rotation angle of the tag in 902 MHz ∼ 928 MHz.