Pattern-Reconfigurable, Circularly Polarized, High-Gain, Archimedean Spiral Antenna Array for Long-Distance, Wide-Coverage RFID Inventorying

A low-cost, pattern-reconfigurable, circularly polarized, high-gain, radio-frequency identification (RFID) reader antenna array is presented. It is a $2\times2$ array whose elements are based on an innovative Archimedean spiral design. A 4-way power divider feed network with switchable delay lines is designed that enables reconfiguring the radiation patterns of the array. Because of its high realized gain and nine reconfigurable states, the developed reader antenna can be applied in long-distance, wide-coverage RFID inventorying. The fabricated prototype, with dimensions $1.15\times 1.15\times 0.07~\lambda _{L}^{3}$ at 920 MHz, achieves a measured axial-ratio (AR) fractional bandwidth of 4.6%, and a peak realized gain (RG) of 10.5 dBic (12 dBic without the feed network). The RG of its reconfigurable patterns is greater than 6 dBic within $\theta $ = $0^{\circ }\pm 45^{\circ }$ for all azimuth angles. It was also tested in an outdoor range as the reader antenna for a practical RFID system. The maximum read distance was 22.3 m.