PLANCK/LFI: an Advanced Multi-beam High Performance mm-wave Optics for Space Applications

The Low Frequency Instrument (LFI) is one of the two instruments onboard the ESA PLANCK satellite foreseen to be launched in 2007. The LFI will image the Cosmic Microwave Background (CMB) anisotropies and the polarization in four different bands, with an unprecedented combination of sky coverage, calibration accuracy, control of systematic errors, and sensitivity. LFI is coupled to the PLANCK Telescope by an array of 23 high performance dual profiled corrugated feed horns. The dual reflector off axis-design of the 1.5 meter projected aperture telescope is the most advanced optical design ever conceived for accommodating large multi-beam and multi-frequency focal plane units. The location and the design of the feed horns, for both instruments, have been optimised in order to maintain good beam symmetry, even far from the optical axis, and an excellent straylight rejection. In this paper we describe the LFI instrument with emphasis on its optical performance and coupling with the PLANCK telescope.