Sequential Phase Feed Based Circularly Polarized RFID Reader Antenna for 2.45 GHz Applications

Abstract

A wideband, circularly polarized (CP) reader antenna is presented for 2.45 GHz RFID systems. To achieve circular
polarization, the antenna features a circular radiating patch on the top layer, fed by a sequential phase feed network located
on the bottom layer. An air gap is introduced between the two layers to minimize dielectric loss, thereby enhancing
directivity and radiation efficiency, which in turn increases overall gain. Cylindrical copper wires passing through the air
gap connect the bottom feed network to the top patch layer. By implementing incremental phase variations across the four
outputs of the feed network, the antenna achieves a −10 dB impedance bandwidth of 650 MHz (2.02–2.67 GHz) and a
circular polarization axial ratio (CP AR) bandwidth of 150 MHz (2.366–2.527 GHz). The antenna exhibits a peak gain of
8.4 dBiC and maintains a symmetric radiation pattern at 2.45 GHz. The physical dimensions of the antenna are 70 × 70 ×
13.2 mm³. The design provides a 3 dB axial ratio beamwidth of 91° and a half-power beamwidth of 63.9° in the X–Z plane
and 64° in the Y–Z plane. An equivalent circuit analysis is performed to better estimate the antenna's performance. The
design is experimentally verified and compared with simulation results. The proposed antenna is particularly suitable for
mobile RFID applications operating at 2.45 GHz, such as inventory management, asset tracking, access control, electronic
toll collection, and medication distribution.