PLANCK Low Frequency Instrument : towards a final imaging of the CMB anisotropies

PLANCK is the third generation of mm-wave instruments designed for space observations of the cosmic microwave background (CMB) anisotropies within the new Cosmic Vision 2020 ESA Science Program. PLANCK will map the whole sky with unprecedented sensitivity, angular resolution, and frequency coverage, and it likely leads us to the final comprehension of the CMB anisotropies. The Low Frequency Instrument (LFI), operating in the 30 / 70 GHz range, is one of the two instruments onboard PLANCK satellite, sharing the focal region of a 1.5 meter off-axis dual reflector telescope together with the High Frequency Instrument (HFI) operating at 100 / 857 GHz. We present LFI and discuss the major instrumental systematic effects that could degrade the measurements and the solutions adopted in the design phase in order to adequately reduce and control them.