SIS flight mixers for band 2 of the HIFI instrument of the Herschel Space Observatory

We present the recently assembled flight models of the SIS mixer units (MU) for band 2 of the HIFI instrument for the Herschel satellite observatory. Design, device fabrication, most of the mixer hardware fabrication, space-qualification, and final assembly are all realized at KOSMA. Thanks to the modular design RF- and IF-performance of different parts of the MU are tested separately before final assembly. Latest test results show a noise temperature between 80 K in the band centre towards 220 K at the upper band edge at 2.8 K operating temperature. The mixer IF-ripple is below 2 dB over a 4-8 GHz bandwidth including the bias-T which provides a very high EMI and ESD protection. The mixer performance and design are discussed under the aspect of the careful trade off between performance, reliability, timely delivery, and resources.