A novel concept for slot coupled circularly polarized patch antenna

Many applications today need compact, low-profile, small, lightweight and low-cost antennas. Microstrip patch antennas meet these requirements which made them very popular. Two main techniques exist to achieve circular polarization in patch antennas. The first consists in creating an asymmetry in the patch shape in order to excite two orthogonal linear modes. The second technique consists in exciting two orthogonal linear modes using two separate feeds. Single fed asymmetrically shaped patch antennas have poor axial ratio bandwidths (ARB) typically smaller than 1% (AR < 3 dB). The disadvantage of the double fed antennas is the relatively large size of the feed network. We present a new concept for single fed circularly polarized microstrip patch antennas with an improved ARB.