ALMA is the largest radio astronomical facility in the world providing high sensitivity between 35 and 950 GHz,
divided in 10 bands with fractional bandwidths between 19 and 36%. Having a lifespan of at least 30 years, ALMA
carries out a permanent upgrading plan which, for the receivers, is focused on achieving better sensitivity and larger
bandwidths. As result, an international consortium works on demonstrating a prototype receiver covering currents Bands
2 and 3 (67 to 116 GHz) which corresponds to a fractional bandwidth of 54%. Here we present the preliminary design,
implementation and characterization of suitable refractive optics. Results indicate an excellent performance in good
agreement with simulations.
We discuss the design and expected performance of STRIP (STRatospheric Italian Polarimeter), an array of coherent receivers designed to fly on board the LSPE (Large Scale Polarization Explorer) balloon experiment. The STRIP focal plane array comprises 49 elements in Q band and 7 elements in W-band using cryogenic HEMT low noise amplifiers and high performance waveguide components. In operation, the array will be cooled to 20 K and placed in the focal plane of a ~0.6 meter telescope providing an angular resolution of ~1.5 degrees. The LSPE experiment aims at large scale, high sensitivity measurements of CMB polarization, with multi-frequency deep measurements to optimize component separation. The STRIP Q-band channel is crucial to accurately measure and remove the synchrotron polarized component, while the W-band channel, together with a bolometric channel at the same frequency, provides a crucial cross-check for systematic effects.
The LSPE is a balloon-borne mission aimed at measuring the polarization of the Cosmic Microwave Background (CMB)
at large angular scales, and in particular to constrain the curl component of CMB polarization (B-modes) produced by
tensor perturbations generated during cosmic inflation, in the very early universe. Its primary target is to improve the
limit on the ratio of tensor to scalar perturbations amplitudes down to r = 0.03, at 99.7% confidence. A second target is
to produce wide maps of foreground polarization generated in our Galaxy by synchrotron emission and interstellar dust
emission. These will be important to map Galactic magnetic fields and to study the properties of ionized gas and of
diffuse interstellar dust in our Galaxy. The mission is optimized for large angular scales, with coarse angular resolution
(around 1.5 degrees FWHM), and wide sky coverage (25% of the sky). The payload will fly in a circumpolar long
duration balloon mission during the polar night. Using the Earth as a giant solar shield, the instrument will spin in
azimuth, observing a large fraction of the northern sky. The payload will host two instruments. An array of coherent
polarimeters using cryogenic HEMT amplifiers will survey the sky at 43 and 90 GHz. An array of bolometric
polarimeters, using large throughput multi-mode bolometers and rotating Half Wave Plates (HWP), will survey the same
sky region in three bands at 95, 145 and 245 GHz. The wide frequency coverage will allow optimal control of the
polarized foregrounds, with comparable angular resolution at all frequencies.
In this paper we present the test results of the qualification model (QM) of the LFI instrument, which is being
developed as part of the ESA Planck satellite. In particular we discuss the calibration plan which has defined
the main requirements of the radiometric tests and of the experimental setups. Then we describe how these
requirements have been implemented in the custom-developed cryo-facilities and present the main results. We
conclude with a discussion of the lessons learned for the testing of the LFI Flight Model (FM).
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.
The Low Frequency Instrument aboard the PLANCK satellite will employ pseudo-correlation radiometers, operating over three broad bands centred at 30, 44 ,and 70 GHz. The radiometer scheme is based on the simultaneous comparison of two input signals, one coming from the sky and the other coming from a reference blackbody at a stable cryogenic temperature (near 4K) as close as possible to the sky temperature (about 2.7K). This choice is made in order to minimize non-white instrumental noise, typically exhibiting a 1/f spectrum. Effects due to the residual offset are minimised with a gain modulation factor applied in software. Fluctuations of the reference signal, due to fluctuation in the cooling chain or to straylight radiation, can also produce a parasitic signal which would mimic a true sky fluctuation. The PLANCK scientific goal of a high precision imaging of the CMB anisotropy requires an accurate characterisation of each part constituting the chain by using tools of modellisation and experimental tests.
In this work we describe the concept of the radiometric chain, its functioning and the main sources of systematic errors, showing how, only with a hard modelling effort, it is possible to characterise, reduce and then remove in the data processing those systematic effects that may in principle compromise the quality of the whole instrument response.