Design of planar near-field RFID reader antenna for liquid tagging

A compact open-loop antenna with magnetic field enhancement is proposed for near-field operations in the ultra-high frequency (UHF) band, which is able to generate a strong and uniform magnetic field in a near-field zone of the open-loop. The open-loop with half-wavelength perimeters is etched on single-layer of FR4 printed circuit board. The fabricated compact antenna with an overall size of a dimension of 66 × 66 × 0.8 mm
³
, achieves an interrogation zone of 60 × 60 mm
²
with good impedance matching and uniform magnetic field distribution over the bandwidth of 918-932 MHz. The measured maximum read range was up to 200 mm under a 30 dBm transmission power when the button near-field tag was attached to a water container.