Planar square quadrifilar spiral antenna for mobile RFID reader

A compact planar square quadrifilar spiral antenna (QSA) for passive UHF radio frequency identification (RFID) reader is proposed and experimentally investigated. The presented RFID reader antenna consists of four spiral antennas which are fed by microstrip feed network and the 4-port antenna matching technique for QSA is used to improve radiation efficiency. Experimental results shows the proposed antenna has peak gain of 0.06 dBic, axial ratio under 3 dB in wanted frequency band, 3-dB beamwidth of 124° with good right hand circular polarization (RHCP) characteristics.