Reduced-size circular polarized antenna for 434MHz RFID systems using meandered bowtie elements with a novel quadrifilar feed

A meander-line antenna fed in quadrifilar fashion for circular polarized (CP) operation is presented. The antenna and feed network are designed to operate in the 434 MHZ RFID/ISM band (432-435 MHz in this application). The four bowtie elements are fed by a 180 power splitter and 90 degree phase shifters to achieve circularly polarized radiation. Initial measurements show good performance in the 432-435 MHz band, with an axial ratio of 0.72 dB at 434 MHz. The CP performance was demonstrated in a 2×1 and 4×1 array with measured axial ratios of 1.5 and 2 dB, respectively. A 3 dB beam width of 65° and 48° for the 3×1 and 4×1 array was also achieved, respectively.