Simple design of broadband circularly polarized two-arm Archimedean spiral antenna

This article presents a broadband circularly polarized two-arm Archimedean spiral antenna with a novel simple feeding method. Contrary to the conventional spiral antenna excited by a vertically or horizontally balun, the presented design is directly fed by a coxial cable with a planar feeding section optimized to provide a broadband input impedance matching. An antenna prototype has been fabricated and measured to validate the concept. Measured results of reflection coefficient and axial ratio show a good performance over a frequency range from 1.0 to 3.5 GHz, equivalent to similar to 111.1%. Within this band, the antenna prototype exhibits bidirectional radiation with broadside gain values of better than 3.6 dBic.