9
views
0
recommends
+1 Recommend
0 collections
    0
    shares
      • Record: found
      • Abstract: found
      • Article: found
      Is Open Access

      Planck-LFI radiometers' spectral response

      Preprint

      Read this article at

      Bookmark
          There is no author summary for this article yet. Authors can add summaries to their articles on ScienceOpen to make them more accessible to a non-specialist audience.

          Abstract

          The Low Frequency Instrument (LFI) is an array of pseudo-correlation radiometers on board the Planck satellite, the ESA mission dedicated to precision measurements of the Cosmic Microwave Background. The LFI covers three bands centred at 30, 44 and 70 GHz, with a goal bandwidth of 20% of the central frequency. The characterization of the broadband frequency response of each radiometer is necessary to understand and correct for systematic effects, particularly those related to foreground residuals and polarization measurements. In this paper we present the measured band shape of all the LFI channels and discuss the methods adopted for their estimation. The spectral characterization of each radiometer was obtained by combining the measured spectral response of individual units through a dedicated RF model of the LFI receiver scheme. As a consistency check, we also attempted end-to-end spectral measurements of the integrated radiometer chain in a cryogenic chamber. However, due to systematic effects in the measurement setup, only qualitative results were obtained from these tests. The measured LFI bandpasses exhibit a moderate level of ripple, compatible with the instrument scientific requirements.

          Related collections

          Most cited references5

          • Record: found
          • Abstract: found
          • Article: found
          Is Open Access

          Planck-LFI: Design and Performance of the 4 Kelvin Reference Load Unit

          The LFI radiometers use a pseudo-correlation design where the signal from the sky is continuously compared with a stable reference signal, provided by a cryogenic reference load system. The reference unit is composed by small pyramidal horns, one for each radiometer, 22 in total, facing small absorbing targets, made of a commercial resin ECCOSORB CR (TM), cooled to approximately 4.5 K. Horns and targets are separated by a small gap to allow thermal decoupling. Target and horn design is optimized for each of the LFI bands, centered at 70, 44 and 30 GHz. Pyramidal horns are either machined inside the radiometer 20K module or connected via external electro-formed bended waveguides. The requirement of high stability of the reference signal imposed a careful design for the radiometric and thermal properties of the loads. Materials used for the manufacturing have been characterized for thermal, RF and mechanical properties. We describe in this paper the design and the performance of the reference system.
            Bookmark
            • Record: found
            • Abstract: found
            • Article: found
            Is Open Access

            The PLANCK LFI flight model ortho-mode transducers

            , , (2010)
            The Low Frequency Instrument (LFI) of the ESA Planck CMB mission is an array of 22 ultra sensitive pseudocorrelation radiometers working at 30, 44, and 70 GHz. LFI has been calibrated and delivered for integration with the satellite to the European Space Agency on November 2006. The aim of Planck is to measure the anisotropy and polarization of the Cosmic Background Radiation with a sensitivity and angular resolution never reached before over the full sky. LFI is intrinsically sensitive to polarization thanks to the use of Ortho-Mode Transducers (OMT) located between the feedhorns and the pseudo-correlation radiometers. The OMTs are microwave passive components that divide the incoming radiation into two linear orthogonal components. A set of 11 OMTs (2 at 30 GHz, 3 at 44 GHz, and 6 at 70 GHz) were produced and tested. This work describes the design, development and performance of the eleven Flight Model OMTs of LFI. The final design was reached after several years of development. At first, Elegant Bread Board OMTs were produced to investigate the manufacturing technology and design requirements. Then, a set of 3 Qualification Model (QM) OMTs were designed, manufactured and tested in order to freeze the design and the manufacturing technology for the flight units. Finally, the Flight Models were produced and tested. It is shown that all the OMT units have been accepted for flight and the electromagnetic performance is at least marginally compliant with the requirements. Mechanically, the units passed all the thermoelastic qualification tests after a reworking necessary after the QM campaign.
              Bookmark
              • Record: found
              • Abstract: found
              • Article: found
              Is Open Access

              The Planck-LFI flight model composite waveguides

              , , (2010)
              The Low Frequency Instrument on board the PLANCK satellite is designed to give the most accurate map ever of the CMB anisotropy of the whole sky over a broad frequency band spanning 27 to 77 GHz. It is made of an array of 22 pseudo-correlation radiometers, composed of 11 actively cooled (20 K) Front End Modules (FEMs), and 11 Back End Modules (BEMs) at 300K. The connection between the two parts is made with rectangular Wave Guides. Considerations of different nature (thermal, electromagnetic and mechanical), imposed stringent requirements on the WGs characteristics and drove their design. From the thermal point of view, the WG should guarantee good insulation between the FEM and the BEM sections to avoid overloading the cryocooler. On the other hand it is essential that the signals do not undergo excessive attenuation through the WG. Finally, given the different positions of the FEM modules behind the focal surface and the mechanical constraints given by the surrounding structures, different mechanical designs were necessary. A composite configuration of Stainless Steel and Copper was selected to satisfy all the requirements. Given the complex shape and the considerable length (about 1.5-2 m), manufacturing and testing the WGs was a challenge. This work deals with the development of the LFI WGs, including the choice of the final configuration and of the fabrication process. It also describes the testing procedure adopted to fully characterize these components from the electromagnetic point of view and the space qualification process they underwent. Results obtained during the test campaign are reported and compared with the stringent requirements. The performance of the LFI WGs is in line with requirements, and the WGs were successfully space qualified.
                Bookmark

                Author and article information

                Journal
                2010-01-26
                Article
                10.1088/1748-0221/4/12/T12010
                1001.4589
                aaad1e30-fdc1-4450-8fbc-b73f6cc5ba71

                http://arxiv.org/licenses/nonexclusive-distrib/1.0/

                History
                Custom metadata
                Journal of Instrumentation, Volume 4, Start page T12010, 2009
                16 pages, 9 figures, this paper is part of the Prelaunch status LFI papers published on JINST: http://www.iop.org/EJ/journal/-page=extra.proc5/jinst
                astro-ph.IM astro-ph.CO

                Cosmology & Extragalactic astrophysics,Instrumentation & Methods for astrophysics

                Comments

                Comment on this article