Spectroscopy with multichannel correlation radiometers

Correlation radiometers make true differential measurements in power with high accuracy and small systematic errors. This receiver architecture has been used in radio astronomy for measurements of continuum radiation for over 50 years; in this article, spectroscopy over broad bandwidths using correlation techniques is examined. After general discussions of correlation and the choice of hybrid phase experimental results from tests with a simple laboratory multichannel correlation radiometer are shown. Analysis of the effect of the input hybrid’s phase shows that a 90° hybrid is likely to be the best general choice for radio astronomy, depending on its amplitude match and phase flatness with frequency. The laboratory results verify that the combination of the correlation architecture and an analog lag correlator is an excellent method for spectroscopy over very wide bandwidths.