Axial ratio improvement of an Archimedean spiral antenna over a radial AMC reflector

This paper presents a method to improve the circular polarization of an Archimedean spiral antenna placed over a radial Artificial Magnetic Conductor (AMC). Results have been compared with the same radiating element over a more classical AMC reflector. A prototype of an Archimedean two-wire spiral antenna has been built to operate from 0.5 GHz to 6 GHz. Measurement results with this radial AMC give a relative bandwidth of 79 %, in which the broadside RHCP gain is improved. In this bandwidth the axial ratio of Archimedean spiral antenna placed over a radial AMC is less than 2 dB whereas it is higher than 3 dB with a classical cartesian shape of AMC reflector.