Broadband circular polarized antenna for 915MHz RFID systems using miniaturized bow-tie loop elements

In this work a new broadband circularly-polarized antenna is presented for ultrahigh frequency (UHF) RFID systems. The antenna is designed to simultaneously cover the European and American RFID/ISM band (860-868 MHz and 902-928 MHz, respectively). The simulated data shows a 10 dB return loss bandwidth covering the frequency range from 846 MHz up to 959 MHz, making the antenna suitable for RFID systems. Furthermore, reductions in length of 31% and occupied footprint of 53% for a single antenna element is achieved. The bowtie element was implemented in a four element circular polarized (CP) design for operation in the 915 MHZ band, fed by a 180 power splitter and 90 degree phase shifters to achieve circularly polarized radiation. Initial measurements show good performance in the 902-928 MHz band, with an axial ratio of 0.72 dB at 915 MHz. Due to the broadband performance of the designed antenna, operation in the European ISM band can be easily achieved by simply replacing the feed and matching network components.