Modeling and Design of a Large Segmented Loop Antenna With a Coplanar Parasitic Slot Loop for NF UHF RFID Readers

This work proposes an improved electrically large antenna based on segmented loops for near-field radio frequency identification readers. The paper applies dispersion analysis of an equivalent circuit model to optimize the segmented loop geometric dimensions and enlarge the tag detection perimeter of the antenna. The novel application of a coplanar parasitic slot loop is shown to improve the dispersion properties of the segmented loop and expand the read perimeter to more than 3.5 times the free-space wavelength at the operating frequency. Furthermore, using the proposed circuit model, a loop antenna with perimeter equivalent to 3.54 times the free-space wavelength is designed and tested for both bidirectional and unidirectional detection. The fabricated prototype demonstrated an improved read range reaching
$25~mm$
for the bidirectional range and
$35\,\,mm {-}55\,\,mm$
for the unidirectional operation setup as well as impedance matching at the design frequency (0.915 GHz) located in the North American RFID band from
$0.902 {-}0.928\,\,GHz$
.