Design, development and verification of the 30 and 44 GHz front-end modules for the Planck Low Frequency Instrument

Abstract

We give a description of the design, construction andtesting of the 30 and 44 GHz Front End Modules (FEMs) for the LowFrequency Instrument (LFI) of the Planck mission to be launched in2009. The scientific requirements of the mission determine theperformance parameters to be met by the FEMs, including their linearpolarization characteristics.The FEM design is that of a differential pseudo-correlation radiometerin which the signal from the sky is compared with a 4-K blackbodyload. The Low Noise Amplifier (LNA) at the heart of the FEM is basedon indium phosphide High Electron Mobility Transistors (HEMTs). Theradiometer incorporates a novel phase-switch design which givesexcellent amplitude and phase match across the band.The noise temperature requirements are met within the measurementerrors at the two frequencies. For the most sensitive LNAs, the noisetemperature at the band centre is 3 and 5 times the quantum limit at30 and 44 GHz respectively. For some of the FEMs, the noisetemperature is still falling as the ambient temperature is reduced to20 K. Stability tests of the FEMs, including a measurement of the 1/fknee frequency, also meet mission requirements.The 30 and 44 GHz FEMs have met or bettered the mission requirementsin all critical aspects. The most sensitive LNAs have reached newlimits of noise temperature for HEMTs at their band centres. The FEMshave well-defined linear polarization characteristcs.