SKA Hybrids and the US LNSD Concept

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SKA Hybridsandthe US LNSD Concept

• Joseph Lazio
• US SKA Consortium
• (Naval Research Laboratory)

Basic research in radio astronomy at the NRL is
supported by the Office of Naval Research.
Partial support for the US SKA Consortium
provided by the NSF.
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SD Contribution to a Hybrid

• Key Science Projects (n gt 5 GHz)
• Strong-field Tests of Gravity using Pulsars and
  Black Holes
• Galactic center pulsars
• Probing the Dark Ages
• High-z CO
• Origin and Evolution of Cosmic Magnetism
• Faraday rotation
• The Cradle of Life
• Biomolecules
• Terrestrial planet formation
• SETI

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Small Dishes

• Advantages
• Based upon well-proven technology and modest
  extrapolations.
• Good high-frequency performance
• Robust to failure

• Challenges
• Low-frequency limit sufficient?
• FoV difficult to expand without potentially
  increasing the data rate dramatically.
• No multi-fielding

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SKA Hybrid

• How to form a hybrid without increasing the
  budget while retaining as much scientific
  capability as possible?
• High- and low-frequency sub-arrays, with SDs
  forming the high-frequency sub-array
• 2500 SDs Cylindrical Reflectors
• 2500 SDs Aperture Arrays

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SKA HybridsHigh- and Low-Frequency Sub-arrays

• High-frequency sub-array 2500 parabolic dishes
  above 0.47 GHz
• Aeff/Tsys 104 m2/K
• Cost 493M.
• Incorporates savings from utilizing symmetric
  dishes
• Low-frequency sub-array 500M
• Infrastructure 376M.
• Cores
• Central processing facility
• Station (96) infrastructure
• Signal processing
• Computing
• System engineering/NRE
• Total (1400 100)M

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SDs in an SKA Hybrid

• Frequency range 0.4724 GHz
• Provide overlap with lower frequency sub-array.
• Provide coverage of H I line to z 2.

• Core configuration
• Science Requirements specify 20 of the
  collecting area within 1 km (diameter) and 50
  within 5 km (diameter).
• Core 5-km diameter region 1250 antennas
• Try to overlap high- and low-frequency cores as
  much as possible for cost savings.

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Core Configuration

• Central 1-km region 500 antennas
• f 5
• Minimum separation 25 m ? minimum unshadowed
  elevation of 26º
• Only a small fraction of the antennas at any
  given azimuth
• Necessary consequence of exploiting
  foreshortening of baselines
• Separate regions for the high- and low-frequency
  arrays
• 750 antennas in 15 km annulus
• Fifty-eight (58) 13-antenna stations or
• Free ranging

500 SDs
1 km
5 km
750 SDs
1250 antennas total
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SD Station Configuration

• Science Requirements specify 75 of the
  collecting area be within 150 km, with the
  remainder spread over approximately 3000 km.
• 48 stations between 5 and 75 km
• 48 stations beyond 150 km
• Minimum antenna separation is 20 m
• FOV 10 at 1.4 GHz
• some shadowing, but not too significant as
  stations used for high resolution studies

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SDs in an SKA

• Feeds
• ATA-like feed Log-periodic design
• Will be extensively tested on the ATA in 2004
• lower system temperature goal of 18 K
• Ingersen feed Extensive test data
• good power patterns
• unacceptable impedance variation with frequency
• Kildal feed Invented recently

• Receivers
• Objective is decade bandwidth receivers with
  acceptable Tnoise
• Cryogenically cooled HEMT receivers ? SiGe and
  InP HEMT MMIC-based amplifiers
• Associated cryogenics are key
• Low power consumption
• Long mean time between failures (MTBFs)
  (claimed) MTBFs of 5 ? 104 hr

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SDs in an SKA

• Fields of View
• 1.5 deg2 at 1.4 GHz
• One (1) FoV with the full array sensitivity
• Sub-arrays ? multiple FoVs, though with less than
  full array sensitivity

Operational considerations Widely separated
frequency bands with a common field of view
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FINITO