Insert subject here

1
An update on APERTIF and the DIGESTIF digital FPA
demonstrator

• Wim van Cappellen
• 27-09-2007

2
APERTIF Overview

• Technically, APERTIF aims to increase the FoV and
  bandwidth of the WSRT by using Focal Plane Arrays
• Optimum use of mechanical infrastructure
• Operational in 2010
• All digital beamforming

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Status APERTIF

• RD focuses on the (current) highest risks of FPA
  technology
• Sensitivity Ae/Tsys
• Dynamic range
• Calibration, stability, wide-field imaging
• Two complementary parallel activities
• Extensive simulation effort
• FPA test platform on the WSRT

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Activities

• Efficient electromagnetic modeling of large
  arrays
• MoM, CBF in combination with ACA
• System analysis
• System noise and sensitivity calculation
• Calibration and wide-field imaging
• Stability, dynamic range
• Optimization
• How to choose weights for different scenarios
• (high sensitivity / low sidelobes / etc)
• Design
• Wideband arrays, room temperature LNAs
• Digital hardware leans strongly on LOFAR
• Demonstrator DIGESTIF
• DIGital Early Stage Tile In Focus

5
APERTIF front-end development planning
FE0
APERTIF
DIGESTIF integrated
RD phase
DIGESTIF stand-alone
Proof of concept Basic architecture
DIGESTIF integrated
Demonstrator architecture Tsys 100 50
K Sensitivity, Calibration, Imaging, Stability
FE0 development
Roll-out
Final architecture Tsys 50 K
2005
2006
2007
2008
2009
2010
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DIGESTIF

• DIGital Early Stage Tile In Focus
• A digital FPA demonstrator in one of the WSRT
  dishes to test and evaluate sensitivity,
  calibration and imaging

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DIGESTIF Characteristics

• Frequency range 1.0 1.7 GHz
• Array size 80 x 80 cm
• Dual linear polarization (vivaldi elements)
• Number of elements 8 x 7 x 2 112
• Instantaneous bandwidth 30 MHz
• Number of receivers 60
• Observation time max 6.7 seconds per measurement
• System temperature 100 K
• Dish diameter 25 m
• Raw data storage enormous flexibility since the
  weighting factors are applied afterwards. This
  allows optimisation of the beamformer weights in
  software without re-measuring!

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Array in the focusbox
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Dual polarised Vivaldi array
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Down Conversion Unit

• Convert input band (1.0 1.7 GHz) to
• LOFAR band (40 80 MHz)

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First Light Galactic HI

• HA04h 46m, Dec45 14' t6.7s Df 9.77 kHz
  (defined in software)

13
First light Driftscan Virgo A

• 0.2s integration per point, 20 MHz bandwidth,
  1420 MHz

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Comparison with simulated patterns

• First order simulation (simulation took
• Satisfactory agreement for now

15
Element pattern measurement

• Used geostationary satellite (Afristar) as point
  source
• Four elements are now operational

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Measured far field beam of single element
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Measured far field beam of single element
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Measured far field beam of single element
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Measured far field beam of single element
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Measured far field beam of single elements
Complex patterns are combined offline, ideal to
experiment and for optimisation
Combination of elements will correct for these
effects
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Focal field distribution

• Single point source on-axis

Simulation
Measurement
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Coming months

• Hardware
• Upgrade from 4 to 60 active elements
• Install LNAs on all 112 elements
• Measurement and analysis of DIGESTIF data

23
SKADS MCCT Technical workshop
Design of Wideband Receiving Array Systems

• Topics of the workshop include
• Antenna array EM modeling and design
• Low noise amplifiers
• Sensitivity calculation of receiving array
  systems
• Low-cost mass production and its impact on
  performance
• Beamforming and digital signal processing
• Measurement and experimental techniques

Guest speakers Prof. A.K. Brown
(Manchester) Prof. C. Craeye (UCL) Prof. P-S.
Kildal (Chalmers) K.F. Warnick (Associate Prof
Brigham Young, US)
Grants are available for EU eligible countries!
http//www.astron.nl/workshop/MCCT/