M. Sandri

High Performance Corrugated Feed Horns for Space Applications at Millimetre Wavelengths

We report on the design fabrication and testing of a set of high performance corrugated feed horns at 30, 70, and 100 GHz, built as advanced prototypes for the Low Frequency Instrument (LFI) of the ESA Planck mission. The electromagnetic designs include linear (100 GHz) and dual shaped (30 and 70 GHz) profiles. Fabrication has been achieved by direct machining at 30 GHz and by electro-formation at higher frequencies. The measured performances on side lobe and return loss meet the stringent Planck requirements over the large (20%) instrument bandwidth. Moreover, the advantage in terms of main lobe shape and side lobe levels of the dual profiled designs has been demonstrated.

The Optical Design of the Background Emission Anisotropy Scanning Telescope (BEAST)

We present the optical design of the Background Emission Anisotropy Scanning Telescope (BEAST), an offaxis Gregorian telescope designed to measure the angular distribution of the cosmic microwave background radiation (CMBR)at30and 41.5 GHzonangularscalesrangingfrom 20 0 to10 � .Theapertureof thetelescope is1.9m, and our design meets the strict requirements imposed by the scientific goals of the mission: the beam size is 20 0 at 41.5 GHz and 26 0 at 30 GHz, while the illumination at the edge of the mirrors is lower than � 30 dB for the central horn.Theprimarymirror isanoff-axissectionofaparaboloid,andthesecondaryanoff-axissectionofanellipsoid.A spinning flat mirror located between the sky and the primary provides a two-dimensional chop by rotating the beams around an ellipse on the sky. BEAST uses a receiver array of cryogenic low noise InP High Electron Mobility Transistor (HEMT) amplifiers. The baseline array has seven horns matched to one amplifier each and one horn matchedtotwoamplifiers(twopolarizations)foratotalofnineamplifiers.Twohornsoperatearound30GHz,andsix operate around 41.5 GHz. Subsequent campaigns will include 90 GHz and higher frequency channels. Subject heading gs: cosmic microwave background — cosmology: observations — telescopes

Trade-off between angular resolution and straylight contamination in the PLANCK Low Frequency Instrument

The last generation of CMB anisotropy experiments operating either from space, like the WMAP and PLANCK satellite, from the atmosphere, such as balloons, or from the ground, like interferometers, make use of complex multi-frequency instruments at the focus of meter class telescopes to allow the joint study of CMB and foreground anisotropies, necessary to achieve an accurate component separation. Between ∼70 GHz and ∼300 GHz, where foreground contamination is minimum, it is extremely important to reach the best trade-off between the improvement of the angular resolution, necessary for measuring the high order acoustic peaks of CMB anisotropy, and the minimization of the straylight contamination mainly due to the Galactic emission. This is one ol the most critical systematic effects at large and intermediate angular scales (i.e. at multipoles f less than 100) and consists in unwanted radiation entering the beam at large angles from the direction of the antenna boresight direction. We consider here the 30 and 100 GHz channels of the PLANCK Low Frequency Instrument (LFI). Assuming the nominal PLANCK scanning strategy, we evaluate the straylight contamination introduced by the most relevant Galactic foreground components for a reference set of optical configurations, accurately simulated as described in Sandri et al. (2004, A&A, 428, 299) (hereafter Paper 1). Given the overall constraints to the LFI optical design, we show that it is possible to improve the angular resolution by 5-7% by keeping the overall peak-to-peak signal of the Galaxy straylight contamination (GSC) below the level of few μK (and about 10 times smaller in terms of rms). A comparison between the level of straylight introduced by the different Galactic components for different beam regions (intermediate and far beam) is presented. We provide approximate relations, both for the intermediate and the far beam, for the rms and the peak-to-peak levels of the GSC as functions of the corresponding contributions to the integrated beam or of the spillover. For some reference cases we compare the results based on Galactic foreground maps derived from radio, IR, and Hα templates with those based on WMAP maps including CMB and extragalactic source fluctuations. The implications for the GSC in the PLANCK LFI polarization data are discussed. Finally, we compare the results obtained at 100 GHz with those at 30 GHz, where the GSC is more critical.

Planck low-frequency instrument: a study on the performances of the Planck millimeter space telescope coupled with LFI feed horns

PLANCK represents the third generation of mm-wave instruments designed for space observations of Cosmic Microwave Background anisotropies within the new Cosmic Vision 2020 ESA Science Programme. The PLANCK survey will cover the whole sky with unprecedented sensitivity, angular resolution, and frequency coverage. The expected scientific return will be enormous, both for the cosmological constraints that will be set and for the gold mine of information contained in the astrophysical foregrounds. To reach these ambitious scientific goals, the control of systematic effects is mandatory and a careful instrument design is needed, as well as an accurate knowledge of instrumental characteristics. 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 a detailed study carried out by the LFI team on the performances of the PLANCK telescope coupled with LFI feed horns, both in the main beam and in the sidelobe region.

Trade - off between angular resolution and straylight contamination in CMB anisotropy experiments. 2. Straylight evaluation

The last generation of CMB anisotropy experiments operating either from space, like the WMAP and PLANCK satellite, from the atmosphere, such as balloons, or from the ground, like interferometers, make use of complex multi-frequency instruments at the focus of meter class telescopes to allow the joint study of CMB and foreground anisotropies, necessary to achieve an accurate component separation. Between ∼70 GHz and ∼300 GHz, where foreground contamination is minimum, it is extremely important to reach the best trade-off between the improvement of the angular resolution, necessary for measuring the high order acoustic peaks of CMB anisotropy, and the minimization of the straylight contamination mainly due to the Galactic emission. This is one ol the most critical systematic effects at large and intermediate angular scales (i.e. at multipoles f less than 100) and consists in unwanted radiation entering the beam at large angles from the direction of the antenna boresight direction. We consider here the 30 and 100 GHz channels of the PLANCK Low Frequency Instrument (LFI). Assuming the nominal PLANCK scanning strategy, we evaluate the straylight contamination introduced by the most relevant Galactic foreground components for a reference set of optical configurations, accurately simulated as described in Sandri et al. (2004, A&A, 428, 299) (hereafter Paper 1). Given the overall constraints to the LFI optical design, we show that it is possible to improve the angular resolution by 5-7% by keeping the overall peak-to-peak signal of the Galaxy straylight contamination (GSC) below the level of few μK (and about 10 times smaller in terms of rms). A comparison between the level of straylight introduced by the different Galactic components for different beam regions (intermediate and far beam) is presented. We provide approximate relations, both for the intermediate and the far beam, for the rms and the peak-to-peak levels of the GSC as functions of the corresponding contributions to the integrated beam or of the spillover. For some reference cases we compare the results based on Galactic foreground maps derived from radio, IR, and Hα templates with those based on WMAP maps including CMB and extragalactic source fluctuations. The implications for the GSC in the PLANCK LFI polarization data are discussed. Finally, we compare the results obtained at 100 GHz with those at 30 GHz, where the GSC is more critical.

Planck Low Frequency Instrument: Beam patterns

The Low Frequency Instrument on board the Planck satellite is coupled to the Planck 1.5 meter off-axis dual reflector telescope by an array of 27 corrugated feed horns operating at 30, 44, 70, and 100 GHz. We briefly present here a detailed study of the optical interface devoted to optimize the angular resolution (10 arcmin at 100 GHz as a goal) and at the same time to minimize all the systematics coming from the sidelobes of the radiation pattern. Through optical simulations, we provide shapes, locations on the sky, angular resolutions, and polarization properties of each beam. (On behalf of LFI Collaboration)

Sources variability with Planck LFI

Planck LFI (Low Frequency Instrument) will produce a complete survey of the sky at millimeter wavelengths. Data stream analysis will provide the possibility to reveal unexpected millimeter sources and to study their flux evolution in time at different frequencies. We describe here the main implications and discuss data analysis methods. Planck sensitivities typical for this kind of detection are taken into account. We present also preliminary results of our simulation activity.

Data analysis of the Planck/LFI ground-test campaign

The ESA Planck mission is the third generation (after COBE and WMAP) space experiment dedicated to the measurement of the Cosmic Microwave Background (CMB) anisotropies. Planck will map the whole CMB sky using two instruments in the focal plane of a 1.5 m off-axis aplanatic telescope. The High Frequency Instrument (HFI) is an array of 52 bolometers in the frequency range 100-857 GHz, while the Low Frequency Instrument (LFI) is an array of 11 pseudo-correlation radiometric receivers which continuously compare the sky signal with the reference signal of a blackbody at ~ 4.5 K. The LFI has been tested and calibrated at different levels of integration, i.e. on the single units (feed-horns, OMTs, amplifiers, waveguides, etc.), on each integrated Radiometric Chain Assembly (RCA) and finally on the complete instrument, the Radiometric Array Assembly (RAA). In this paper we focus on some of the data analysis algorithms and methods that have been implemented to estimate the instrument performance and calibration parameters. The paper concludes with the discussion of a custom-designed software package (LIFE) that allows to access the complex data structure produced by the instrument and to estimate the instrument performance and calibration parameters via a fully graphical interface.

Millimeterwave tests on passive components of PLANCK-LFI

PLANCK is the ESA mission devoted to cosmic microwave background (CMB) to be launched in 2007. After COBE and WMAP pioneering work, PLANCK is designed to measure the anisotropy spectrum to the full extent of cosmological relevance and make quantitative measurements of CMB polarization. Its optical system consists of a Gregorian telescope coupled with two instruments on the focal surface: the High Frequency Instrument (HFI), an array of bolometers covering the spectral range from 84 GHz to 1 THz; and the Low Frequency Instrument (LFI), an array of pseudo-correlation radiometers spanning the range from 27 to 77 GHz in three 20% frequency bands. We measured vector patterns and return loss of feed horns and S parameters of OMTs and waveguides, obtaining good agreement with the very demanding design specifications.

Millimeterwave Techniques For Fusion Plasmas And For Experimental Cosmology

The millimetric region of the electromagnetic spectrum is of great interest both to plasma physics and to experimental cosmology. Building on the common technological interest, the tests on passive components of the Low Frequency Instrument of the PLANCK mission are made in IFP’s microwave laboratory. The experimental techniques and sample results are shown.