Study of a Multi-Loop Travelling Wave UHF RFID Near-Field Antenna

A multi-loop travelling-wave ultra-high frequency (UHF) radio frequency identification (RFID) near-field antenna (NFA) is proposed and investigated. To achieve strong and uniform magnetic field, as well as extendable reading range, multiple
$\lambda $
/2 rectangular loop structures printed on both sides of an FR4 substrate is adopted. Via the RFID system measurement for magnetic field distribution, the maximum reading range of the proposed NFA is 11 cm, and its corresponding 100% reading rate distance is 5 cm. Here, broad 10-dB impedance bandwidth of 18.7% (816–984 MHz) was measured, which can cover both ETSI (European Telecommunication Standards Institute) and FCC (Federal Communications Commission) bands. Parametric studies are further carried out to facilitate the design and optimization processes.