<title>LO path built-in SIS mixer for further improvement of noise performance</title>

Abstract

In millimeter and submillimeter wave band, radio telescopes' observing efficiency and weak signal detecting capability have been greatly raised in the past tens of years, due to the application of the SIS mixers as their receiver front-ends. However general local power injection methods for a heterodyne receiver usually result in additional insertion loss which degrades sensitivity of SIS receivers. Based on the extremely small local power requirements of SIS quantum mixing, we developed a novel LO path built-in SIS mixer, in which an additional waveguide was built for LO power injection. Without any of traditional external LO diplexers (e.g., crossguide- couplers or beamsplitters), LO power is provided to SIS junctions through the LO waveguide and the junction chip which connects both LO- and signal waveguides. There is no RF signal lost due to coupling LO power since LO- and RF signal take different paths before arriving at junctions, resulting in a compact, stable and lower loss SIS receiver system. Experiments at 110- and 230 GHz bands show that there is no any problem to couple sufficient pumping power to SIS junctions from general LO sources for present LPB mixer, and the receiver sensitivities have a further improvement of about 10 K compared to our previous beamsplitter LO power coupling receiver system. We expect this LPB SIS mixer can be also applied into submillimeter wave band.