The Planck-LFI flight model ortho-mode transducers

Abstract

The Low Frequency Instrument (LFI) of the ESA Planck CMB mission is anarray of 22 ultra sensitive pseudocorrelation radiometers working at30, 44, and 70 GHz. LFI has been calibrated and delivered forintegration with the satellite to the European Space Agency onNovember 2006. The aim of Planck is to measure the anisotropy andpolarization of the Cosmic Background Radiation with a sensitivity andangular resolution never reached before over the full sky.LFI is intrinsically sensitive to polarization thanks to the use ofOrtho-Mode Transducers (OMT) located between the feedhorns and thepseudo-correlation radiometers. The OMTs are microwave passivecomponents that divide the incoming radiation into two linearorthogonal components. A set of 11 OMTs (2 at 30 GHz, 3 at 44 GHz, and6 at 70 GHz) were produced and tested. This work describes thedesign, development and performance of the eleven Flight Model OMTs ofLFI.The final design was reached after several years of development. Atfirst, Elegant Bread Board OMTs were produced to investigate themanufacturing technology and design requirements. Then, a set of 3Qualification Model (QM) OMTs were designed, manufactured and testedin order to freeze the design and the manufacturing technology for theflight units. Finally, the Flight Models were produced and tested.It is shown that all the OMT units have been accepted for flight andthe electromagnetic performance is at least marginally compliant withthe requirements. Mechanically, the units passed all the thermoelasticqualification tests after a reworking necessary after the QMcampaign.