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 degrees 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 x 0.22 x 0.05 lambda(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.