Ultra low noise and high stability receivers of Planck LFI

Design concept and development of the Low Frequency Instrument (LFI) for ESA's Planck Surveyor mission is described. The LFI is a multifrequency radiometer array designed to cover the 30–100 GHz spectral range. The goal is to perform a deep, full-sky imaging of the microwave sky and to extract the wealth of cosmological information imprinted in the Cosmic Microwave Background anisotropy pattern. The LFI will survey the sky at four frequencies (30, 44, 70 and 100 GHz) with unprecedented accuracy using state-of-the-art, cryogenic, coherent receivers based on low-noise Indium Phosphide high-electron-mobility transistor amplifiers cooled at an operating temperature of 20 K. The main instrument requirements, design drivers and sources of potential systematics are discussed.