Wideband circularly polarized microstrip-parallel strip-fed spiral antenna

A microstrip-parallel strip-fed circularly polarized spiral antenna is investigated. A wideband microstrip to parallel strip transition is designed in order to feed the spiral antenna. The transition shows a back-to-back return loss of better than 10 dB from 0.045 to 20 GHz except for a ripple at 2 GHz, while the back-to-back insertion loss is less than 2.4 dB. The final antenna shows a return loss of better than 10 dB from 2.5 to 13.5 GHz. The antenna axial ratio is better than 2.2 dB from 5 to 12 GHz.