Sideband separating mixer for 600-720 GHz for ALMA band 9 upgrade

For high-frequency observational bands like ALMA (Atacama Large Millimeter Array) Band 9 (600—720 GHz), which tend to be dominated by atmospheric noise, implementation of sideband-separating mixers can reduce, up to a factor of two, the integration time needed to reach a certain signal-to-noise ratio for spectral line observations. Because of very high oversubscription factor for observation in ALMA Band 9, an upgrade of the current Double Sideband (DSB) mixer to a Two Sideband (2SB) configuration is a promising option for future ALMA development. Here we present a developed 2SB mixer and a modified cartridge design. The 2SB mixer includes a waveguide RF hybrid block, which have been produced on a micro-milling machine and equipped with standard Band 9 SIS mixer devices. These two SIS mixers have been separately tested in DSB mode. The SSB noise temperature is within the ALMA requirements of 336 K over 80% of the band, and 500 K over the entire band. The 2SB mixer has the sideband rejection ratio better than 12 dB over the full RF band, which is also well within the ALMA specifications of 10 dB.