Highligh in Physics 2005

1

• Congresso del Dipartimento di Fisica
• Highlights in Physics 2005
• 1114 October 2005, Dipartimento di Fisica,
  Università di Milano
• Calibration and testing of the Planck-LFI
  instrument
• A. Mennella, M. Bersanelli, D.Maino, M.
  Tomasi,, B. Cappellini, S. Pezzati, O.
  DArcangelo, L. Figini, S. Garavaglia, P.
  Platania, A. Simonetto, C. Sozzi, P.
  Battaglia?, C. Franceschet?, M. Lapolla ?, and P.
  Leutenegger?
• Dipartimento di Fisica, Università di Milano,
  INAF- IASF, Milano, IFP - CNR, Milano,
  ?Alcatel Alenia Spazio

Planck, an ESA mission scheduled for launch in
2007, is the third generation of CMB anisotropy
space mission planned to fully map the sky
emission with an unprecedented combination of
frequency coverage (30-857 GHz), angular
resolution (30 to 5) and sensitivity (few ?K
per resolution element). The Planck-LFI
instrument is an array of 11 pseudo-correlation
radiometric receivers in three frequency bands
centred at 30, 44 and 70 GHz. The testing and
calibration phase of this instrument is carried
out in three main phases (I) testing performed
at unit level, (ii) testing and calibration of
each radiometric chain and (iii) testing and
verification of the whole integrated LFI
instrument. In this poster we present the results
obtained during the QM (Qualification Model)
testing campaign with particular emphasis to the
calibration of the individual radiometric chains.
List of main radiometric tests List of main radiometric tests
Tuning tests Tuning tests
Dynamic range optimisation The objective is to find the optimal conditions to to adapt the input signal at the ACD dynamic range and the best bias conditions to the front-end amplifiers and phase switches.
Phase switch balance The objective is to find the optimal conditions to to adapt the input signal at the ACD dynamic range and the best bias conditions to the front-end amplifiers and phase switches.
Amplifier bias tuning The objective is to find the optimal conditions to to adapt the input signal at the ACD dynamic range and the best bias conditions to the front-end amplifiers and phase switches.
Basic performances (from data acquired at different temperature inputs) Basic performances (from data acquired at different temperature inputs)
Noise temperature, calibration constant, linearity, input offset These parameters are determined from data acquired during a ramp in the sky-load temperature.
Receiver bandwidth Determined by a dedicated test in which the input signal is a monochromatic wave swept through the receiver bandpass (swept source test, done only at RCA level)
Noise properties (from data acquired at stable input and boundary conditions) Noise properties (from data acquired at stable input and boundary conditions)
1/f noise, white noise limit and noise effective bandwidth From data acquired in stable conditions we calculate the power spectral density, from which the basic noise properties are derived.
Receiver susceptibility Receiver susceptibility
To variations in boundary temperatures These test are performed by changing the temperature at a given boundary or the bias input voltage and recording the radiometric output.
To variations in input bias voltages These test are performed by changing the temperature at a given boundary or the bias input voltage and recording the radiometric output.
The RCA (Radiometer Chain Assembly) is a complete
independent differential radiometric chain
collecting the sky signal by means of a
corrugated feed horn. Each RCA is tested and
calibrated independently before being integrated
in the LFI instrument. RCAs at 30 and 44 GHz are
integrated and tested at Alcatel-Alenia Spazio
S.p.A. (Vimodrone, Milano) in a custom designed
cryofacility. RCAs at 70 GHz are integrated and
tested at Ylinen (Helsinki, Finland). The LFI QM
is constituted by one RCA at 30 and 44 GHz and by
2 RCAs at 70 GHz.
The RAA (Radiometer Array Assembly) is the
complete array of radiometric chains integrated
in the mechanical structure. The RAA is
integrated and tested in Alcatel Alenia Spazio
(Vimodrone, Milan) in a custom designed
cryofacility developed by CSL (Liegi, Belgium).
The QM LFI instrument
Details of the RCA
Bipods
Waveguides
CAD 3D model of the LFI instrument. The
feed-horns and the front-end modules of the
radiometers are integrated into an aluminum
structure (the main-frame) interfaced to the
satellite by bipods. The waveguides carry the
radiometric signal from the 20K front-end to the
300K back-end. Three radiative shields (so-called
V-grooves) allow an effective dissipation into
space of the heat coming from the warm stage. In
the central part of the focal plane the
feed-horns of the HFI instrument are visible
The 44 GHz RCA integrated on the cryofacility
workbench. Attached to the feed-horn an OMT
(Orthomode Transducer) separates the incoming
wave into two orthogonally polarised components.
Each wave is amplified and compared with a stable
signal from a 4 K black body. Further RF
amplification is provided at room temperature
before detection. Waveguides follow a complex
routing for mechanical integration purposes and
are made by different materials to optimise
thermal and radiometric performances. Below, in a
close-up of the radiometer front-end, we show the
OMT, the Front-end Module and the two waveguides
that carry the reference signal from the
reference loads to the front-end module.
waveguides
back-end module
OMT
Front-end unit
Feed horn
Back-end unit
The input sky load, a black body
custom-designed by IASF Bologna to provide and
adapted input with lt -30 dB return loss. The
feed-horn faces an ECCOSORB bed through the hole
visible in the figure. The flexible waveguide is
used to inject a monochromatic signal in the
swept source test (see below)
The QM LFI instrument during integration in the
Alcatel-Alenia Spazio laboratories in Vimodrone
(Milano). The instrument is supported by a custom
Ground Support Equipment that is removed once
integrated in the cryofacility
4K reference loads
A test in more detail the swept source test
waveguides
The QM LFI instrument integrated into the
cryochamber in the Alcatel-Alenia Spazio
laboratories in Vimodrone (Milano). An ECCOSORB
bed is placed below the focal plane and
constitutes the sky load, i.e. the black body
that provides the input signal to the
radiometers.
back-end unit (300K)
Schematic of the swept source test. A
monochromatic wave in injected into the RCA feed
horn at various frequencies in the receiver band
by means of a flexible waveguide. The radiometric
output is recorded and the power is plotted
against frequency. On the QM instrument the test
has been run only with the 30 GHz radiometer
front-end unit (20K)
The receiver effective bandwidth is defined as
and depends on the characteristics of the
radiometer gain function. The bandpass measured
by the swept source test matched simulation
results obtained with a numerical model of the
LFI receivers. The measured effective bandwidths
at 30 GHz were 6 GHz, consistently with the
required value.
sky load (20K)
Data analysis software
An IDL software package has been developed to
analyse the data produced during the RCA and RAA
testing campaigns. The software, named LIFE (Lfi
Integrated perFormace Evaluator) is constituted
by two main modules RaNA (Radiometer aNAlyser),
used to analyse data produced by individual
radiometers during the RCA tests, and LAMA (Lfi
Array Measurements Analyser) used to analyse the
data from the complete array during the RAA
tests. In the figures we show some snapshots of
the software. More info on http//lucifer.mi.iasf.
cnr.it/web/rana
The data viewer. This interface allows to
navigate interactively into radiometric and
housekeeping data.
The RaNA and LAMA main windows