Compact Circularly Polarized Meandered-Loop Antenna for UHF-Band RFID Tag

A planar loop antenna design for ultra-high frequency radio frequency identification (UHF RFID) operating in the 922-928 MHz band is investigated. To achieve compact size of 58.6 × 58.6 mm
²
for this loop antenna, the technique of using meandered-loop structure is applied, and by further introducing an open gap into this meandered-loop, good circularly polarized (CP) radiation is also attained. Desirable impedance matching between the meandered-loop antenna and RFID chip is achieved by applying a simple matching stub. Besides exhibiting satisfactory 3-dB axial-ratio (AR) bandwidth of 921-929 MHz and 10-dB impedance bandwidth of 915-942 MHz, good antenna gain of 1.73 dBic and long read range of up to 20.5 m are also demonstrated.