A Compact Circular Polarization Antenna Using Folded Ground Elements

This communication presents a new antenna structure using a folded ground element (FGE) for a compact antenna implementation. The proposed FGE is analyzed with an equivalent circuit model where equivalent capacitances and inductances of the proposed antenna are included. Also, slot patterns are integrated into a radiation patch element, resulting in a further reduction in the overall antenna size. To verify the proposed antenna with FGEs, an RFID antenna module with a right-handed circular polarization (RHCP) feed network was implemented and tested. The fabricated antenna size was
$100\times 100\times 12\,\,{\mathrm{ mm}}^{3}$
(
$0.29\,\,\lambda _{0} \times 0.29\,\,\lambda _{0} \times 0.03\,\,\lambda _{0}$
at 868 MHz), showing a significant reduction in size compared to the conventional structures. The measured reflection coefficient for the feed network was better than 10 dB from 610 to 950 MHz, and 3 dB axial ratio (AR) bandwidth was about 137 MHz (817–954 MHz). Also, the measured peak gain and AR at 868 MHz were 4.6 dBic and 0.6 dB, respectively.