A Sideband-separating Receiver with a Calibrated Digital If-Hybrid Spectrometer for the Millimeter Band

Abstract

Due to its advantages over other configurations, sideband-separating receivers are usually preferred for radio astronomy, particularly in the presence of high atmospheric noise. However, even with all the advances that have been made in recent years in the field of receiver technology, one of the most important figures of merit for this kind of receiver, the sideband rejection ratio, is still relatively low and typically around 10 to 20 dB. This is because keeping low amplitude and phase imbalances over large RF and IF bands is extremely difficult. In order to overcome this problem, it has been suggested that by introducing a digital back-end that mimics the performance of an IF-hybrid, such imbalances can be calibrated out. Until now, this has been demonstrated only at very low RF frequencies (below 4 GHz). Here, for the first time, we demonstrate that this technique can be applied at higher frequencies. We have implemented a sideband-separating receiver with a calibrated digital IF-hybrid spectrometer for the 3 mm band, and have demonstrated that, even in the presence of large imbalances of individual components, sideband ratios above 35 dB can be obtained in the entire RF band.