Low-Cost Compact Circularly Polarized Dual-Layer PIFA for Active RFID Reader

This communication presents a novel single-fed compact circularly polarized (CP) dual-layer planar inverted-F antenna (PIFA). The proposed antenna is composed of two stacked orthogonal-orientated PIFAs which can be fabricated by elaborately folding one piece of metal plate. The two PIFAs can be excited synchronously with equally allocated power by a single probe, thus a pair of orthogonal polarizations is created. Moreover, the resonant lengths of the upper and lower PIFAs are slightly different from each other to acquire 90° phase shift between the two orthogonal polarizations. Consequently, a right-hand CP radiation is achieved, and the boresight realized gain is 3.8 dBic at the center frequency. The proposed dual-layer PIFA with two quarter-wavelength resonators provides a novel solution for the compactness of CP antennas. To validate the performance of the antenna, a prototype was fabricated and measured. The measured -10 dB impedance bandwidth and 3 dB axial ratio bandwidth are 7.4% and 1.1%, respectively, with a compact antenna volume of 0.26 × 0.22 × 0.05 λ
₃
⁰
. The proposed antenna is a good candidate for the 433 MHz CP active radio-frequency identification reader, and it has the merits of compact size, lightweight, high efficiency, and low cost.