Controlling the THz heterodyne — Lesson learned from HIFI/Herschel mission

The Local Oscillator Subsystem (LOS/S) is a part of the HIFI (Heterodyne Instrument for the Far Infrared) project, an infrared heterodyne instrument for astronomical observations on the ESA HERSCHEL Space Observatory. Local Oscillator Subsystem uses the set of sensitive microwave components, essential for frequency multiplication from K/Ka Bands to 480/1910GHz. The paper presents the methods of biasing of the LOU independent microwave amplifiers and diodes. The special care at the design phase was given to different methods of protection against wrong biasing of such components. The results of the protection, implemented in LCU hardware and software, are discussed at the paper, based on the lessons learned from more than four years of pre-launch activities and almost three years of HIFI operations on the orbit.