Comprehensive Description of Sideband Ratio of 2SB SIS Receiver

Sideband Ratio or so called Image Rejection Ration (IRR), is one of the key figures of merit of sideband separating (2SB) receivers. Although these kind of receivers are widely used in ground-based astronomy, a full description of their IRR pattern has not been performed yet. To solve this problem we have simulated the entire 2SB SIS receiver by combining models of RF and IF chains. It was found that a bottle neck of the IRR performance is not in an imbalance of individual RF and IF components, but in system imbalances determined by parasitic reflections in RF and IF chains. Using that knowledge we have built a 2SB receiver based on SIS mixers for the APEX telescope in Chile, which has a state-of-the-art performance at frequencies 600-720 GHz.