A compact broadband circularly-polarized patch antenna with wide axial-ratio beamwidth for universal uhf rfid applications

Abstract

A compact broadband circularly-polarized (CP) patch antenna with a wide 3-dB axial-ratio (AR) beamwidth is proposed for universal ultra-high-frequency (UHF) radio frequency identification (RFID) applications. The proposed antenna consists of four triangular radiation patches and a compact feed network. Each of the radiation patches is grounded by shorting pins for 3-dB AR beamwidth enhancement and patch miniaturization. The feed network having a miniaturized hybrid coupler and two trans-directional couplers is proposed for good circular polarization. Measured results show that the −10-dB impedance bandwidth of the antenna is 18.4% (820–986 MHz); the 2.5-dB AR bandwidth is 32.8% (700–975 MHz); and the gain is 5.12 dBic. The measured 3-dB AR beamwidths for the planes of phi = 0◦ and phi = 45◦ are 177◦ and 190◦, respectively. The overall antenna size is 0.408λ0 × 0.408λ0 × 0.053λ0 at 900 MHz.