SIS based mixers development for radio astronomy

Superconductor-insulator-superconductor (SIS) mixers are used in the most sensitive heterodyne receivers for sub-mm and mm waves. SIS mixers are installed on all state of the art sub-mm observatories such as the Atacama Pathfinder Experiment (APEX) and the Atacama Large Millimeter Array (ALMA). While sensitivity of an SIS mixer is quantum limited a current state of the art performance of receiver systems can still be improved. In this report we summarize our development effort to improve SIS mixer performance in several frequency bands that are relevant for the ground based astronomy. We have calculated, fabricated and measured a optimized mixer design for the 211-275 GHz frequency range, which could be used for LLAMA observatory in Argentina, for the Millimetron space mission and additional stations in the VLBI network of the Event Horizon Telescope. For the near future development we consider a 2SB mixer design for the 211-275 GHz which is conceptually close to the successful ALMA Band 9 2SB mixer. A receiver is based on single SIS mixer connected to RF hybrid block. The mixer design was developed using 3D electromagnetic modeling in CST microwave studio. The mixer is based on Nb/AlOx/Nb SIS junction embedded in a Nb/SiO2/Nb microstrip line. A good matching between a 500x1000 µm waveguide and the SIS junction was achieved by using quasi-triangle orthogonal waveguide single-sided or double-sided probes. We improved further our modeling approach for the Band 9 mixers which demonstrated an IF bandwidth of up to 20 GHz. We also optimized a mixer design for 790-950 GHz band. The mixer description and achieved performances will be presented at the conference