Compact UHF RFID Handheld Reader Antenna and Array Based on Resonant Quadrifilar Spiral Structure

In this paper, a compact circularly polarized antenna based on a resonant quadrifilar spiral structure for the application of UHF RFID handheld reader is proposed and demonstrated experimentally. To reduce antenna size and improve impedance matching, the original resonant arms are revised by bending inverted-F structures and printing them on dielectric substrates, and the four arms are fed by a four-way phase shift network. Such an antenna indicates stable circular polarization performance and wide beamwidth. The gain bandwidth (> 2 dBic) can cover the frequency band from 902MHz to 928MHz, which is suitable for most of the popular UHF RFID systems in the world. Moreover, the 1×4 array and 2×2 array based on previously demonstrated antenna unit are numerically investigated. The array performances, including the gain, beam scanning and low side-lobe are discussed.