Design of an ultra-broadband high-gain circularly polarized antenna

This paper presents an ultra-broadband high-gain circularly polarized antenna. The antenna is in the form of planar spiral structure and loads resistors at the end of the radiation strips to expand its bandwidth. At the same time, a PEC cavity with a height of
$\lambda/4$
is designed below the radiation plane to produce a unidirectional beam and increase the gain. The final design realizes a broadband impedance matching in 0.5~8GHz (176.5%), AR<3dB in 0.5~7.5GHz (175%) and the highest gain reaches more than 13dBi.