18-45-GHz sideband-separating downconverter with RF image rejection calibration

Abstract

We present a sideband separating downconverter for radio astronomy applications, featuring radio frequency image rejection calibration for frequencies between 18 and 45 GHz. The multichip module optimizes image rejection for specific target observation frequencies by injecting a modulated portion of the Q-branch signal into the I-branch with independent upper and lower sideband injection control. Measurements demonstrate an average image rejection ratio improvement of 9 dB over a 7-GHz band of interest compared with a baseline uncalibrated operation, with improvement of over 40 dB in targeted subbands.