Miniaturized Circularly Polarized Periodically Structured Surface Antenna for RFID Application Inspired by SRR

This article presents a novel miniaturized circularly polarized (CP) antenna based on periodically structured surfaces inspired by the vertical split-ring resonator (VSRR). The VSRR is considered as a magnetic dipole placed above the ground, which could excite strong boresight radiation with a reduced size. To enhance the aperture gain, multicapacitors and inductors (Multi-C&L) are loaded on the loop, which replace the single capacitive gap of the conventional split-ring resonator (SRR). Here an SRR-inspired periodic structure with a relatively uniform field distribution is achieved. The stepped impedance resonator (SIR) structure, as the unit cell of the SRR-inspired surface, is analyzed and investigated using the circuit models derived from the SRR. By cascading multiple high-value capacitors, a larger aperture with a uniform field distribution is obtained. Linearly polarized (LP) and CP antennas are studied. The proposed CP antenna is made of thin substrates and metallic screws, resulting in a negligible dielectric loss. It offers attractive features including a compact size, a low profile (
$0.191\lambda _{0} \times 0.191\lambda _{0} \times 0.032\lambda _{0}$
), good radiation efficiency, novel working principle, flexible performance control, and a bandwidth well covering the 902–928 MHz UHF band, which is well situated for radio frequency identification (RFID) application.