Low profile cavity-backed four-arm Archimedean spiral antenna with 8:1 bandwidth

A wideband circularly polarized, four-arm Archimedean spiral antenna backed by a low-profile metallic cavity of 15 mm (0.03λ at the lowest frequency) with a 8:1 bandwidth from 0.6 GHz to 5 GHz is presented. A feed network comprising of a 90° wideband hybrid connected to two 180° hybrids excites the spiral antenna in the fundamental mode. For the entire 8:1 bandwidth, the measured input return loss of the system is more than 11.4 dB. Despite the low-profile cavity, the measured boresight gain and axial ratio of the antenna is -1 to 8.7 dBi and less than 2 dB respectively.