Compact wideband circularly-polarized antenna for universal UHF RFID handheld reader

A compact wideband circularly-polarized (CP) RF identification (RFID) handheld reader antenna based on inverted-F antennas (IFAs) is proposed. The antenna consists of an upper layer of rotationally symmetric radiation structure and lower layer of feed network. Firstly, the feed network is verified by microwave circuit simulation software. Then the antenna is modeled and simulated with the aid of the full-wave electromagnetic simulation software. Finally, a prototype is fabricated using FR4 plate and its performance of the proposed antenna is validated. The measured impedance bandwidth of 10 dB and the axial ratio (AR) bandwidth of 3 dB are wider than 13%. The peak gain is greater than 2.2 dBic, and the minimum AR is less than 1.1 dB, with the symmetrical and stable radiation patterns. The antenna has the compact size of 60 x 60 x 15 mm(3). The proposed antenna can not only meet the requirements of RFID handheld reader applications in universal ultra-high frequency (UHF) band (840-960 MHz), but also has the advantages of wideband, small size, lightweight, low cost, and simple structure. Therefore, the design has a good application prospect in the field of Internet of Things.