Planar square quadrifilar spiral antenna for mobile RFID reader

A compact wideband circularly polarized quadrifilar antenna with PIFA elements for UHF RFID readers

“…The proposed antenna offers a good combination of relatively compact size, simple fabrication, relatively high gain, and very large impedance matching as well as AR bandwidth with a directional pattern. The gain variation over a bandwidth of 1 dB provided by the proposed antenna is the lowest compared to state-of-the art quadrifilar antennas from [10][11][12][13][14][15]. In the last column, the relative size of each antenna is provided.…”

“…State-of-the-art circularly polarized UHF RFID reader antennas in the literature fall into two categories, truncated patch or annular ring antennas [5][6][7][8][9] and quadrifilar antennas [10][11][12][13][14][15]. Truncated patch antennas generate circular polarization by truncation of the square patch's corners in one of the diagonals.…”

“…If lower antenna gain is acceptable, the size of the antenna can be reduced. In the case of wideband UHF RFID reader antenna with unidirectional pattern, quadrifilar antennas with four radiator elements and a feed network have been reported in the literature [10][11][12][13][14][15]. The feed network divides the input power equally before feeding to each radiator element with a sequential 90°phase shift to generate the circular polarization.…”

“…The peak gain of [9] is observed at 915 MHz with 2.6 dBic, whereas at the lower and upper band limits of 860 and 960 MHz, the gain is drastically decreased to −4.4 and −1.8 dBic, respectively. In comparison, the designs from [11][12][13] and [15] provide smaller bandwidths, especially regarding the AR which are not sufficient to cover the global UHF RFID band.…”

Compact Uhf Rfid Handheld Reader Antenna and Array Based on Resonant Quadrifilar Spiral Structure

“…Most of those designs realize circular polarization by integrating a four-way phase shift network. Moreover, researchers proposed a type of printed square quadrifilar spiral antenna for the UHF RFID handheld reader applications [21,22]; however, the performance is not good enough. Quite recently, researchers have developed an universal UHF RFID handheld reader antenna with rotated inverted-F antennas [23], while the antenna size is not compact enough.…”