W band power amplifier development for the Herschel HIFI instrument

This paper summarizes the development of W Band amplifiers for the Local, Oscillator (LO) chains for the Herschel HIM (Heterodyne Instrument for Far Infrared) Instrument. Key amplifier development issues and their solutions are presented, which have been applied on the way to realizing stable, wide-band amplifiers capable of producing 240 mW or greater RF power output across the 71 to 106 GHz frequency range. The HIM power amplifier design embodiment is based on an A-40 silicon-aluminum alloy package with six GaAs(Gallium Arsenide) HEMT(High Electron Mobility Transistors) MMIC(Monolithic Microwave Integrated Circuit) amplifier chips used in each amplifier. Development challenges addressed include: MMIC chip designs which initially had a variety of oscillation or "moding" propensities (mostly out-of-band), signal splitter and combiner development and matching across the band, matching of chip characteristics for those chips installed in the parallel power combined arms of the amplifier, power output control and leveling. The chosen design solutions are presented, including device, component and material selection for amplifier operation at cryogenic temperatures. Room temperature and cryogenic (120 Kelvin) data is also shown for the amplifier.