Novel circular polarization antenna for UHF RFID application

In this paper, a novel antenna for UHF RFID tag with circular polarization is proposed. The antenna is comprised of two diagonal dipoles with unequal slots to produce circularly polarized (CP) radiation and a simple tunable matching network. The measured result for power reflection coefficient (PRC) is 35 MHz (894–929 MHz) and its corresponding simulated 3-dB axial-ratio (AR) bandwidth is about 31 MHz (903–934 MHz). The overall antenna size is 0.21λ
0
× 0.21λ
0
× 0.003λ
0
at 915 MHz and the maximum simulated gain is about −2.8 dB. The experimental results verify a perfectly RHCP radiation.