Broadband Ka-band 90° phase switch for radio astronomy

A broadband 90° phase switch based on microstrip bandpass filters (BPFs) is presented. The phase shift expression is derived from the theoretical analysis of π-network BPFs. The broadband behaviour is performed and validated in the Ka-band focused on radioastronomy applications. The commutation between networks is achieved by a single-pole double-throw switch with negligible power consumption. Measured results show an average phase shift of 88° ± 6° in the frequency band from 24 to 37 GHz (more than 42% relative bandwidth), with an amplitude imbalance of around 0.5 dB. The return loss is better than 15 dB. Experimental results demonstrate its suitability to be used in broadband radio astronomy receivers.