Justin Jonas

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LNSD SP-WBF

• Small/medium diameter dishes plus single-pixel
  wideband feeds

2
Overview

• JLJ
• Introduce concept, reference specifications and
  technical issues
• JMC
• Implications for science
• Metrics
• Extreme arrays

3
General

• Minimum (but not low) risk mid-band SKA scenario
• Known and tested concept, but e.g.
• no WBF currently performing as well as
  traditional RA feeds
• no existing correlator with gt100 stations
• Sensitivity provided by large N
• Sensitivity ? ND2
• FoV provided by small D
• SSFoM ? (ND)2
• Preferred high(er) band implementation

4
Reference Specifications
ATA
N3109
N1925
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Large N
Need to achieve good Ae/Tsys All survey speed
metrics ? (Ae/Tsys)2
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Small D
Primary Beam FoV ? (?/D)2 scaling
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Trades and Optimization

• Primary trade/optimization parameter is dish
  diameter
• SKA cost model tool used
• Caveats
• See Memo 92 and/or web interface for coefficients
  exponents
• Includes optimistic predictions for processing
  and replication cost reductions

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Diameter optimization - fixed Ae/Tsys
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Diameter optimization - fixed SSFoM
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Technical Challenges - Dishes

• Large N
• Major cost driver
• Manufacturability
• Dish diameter
• large enough to satisfy 20? criterion at Flow
• small enough to support suitable Fhigh
• Clean and time-independent beam
• Optical configuration and mount geometry
• Developments
• Canada, South Africa, USA

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Tyrany of Ruze
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Technical Challenges - WBFs Receivers

• 101 frequency coverage with good
• Return loss
• Illumination pattern
• Xpol
• Ohmic losses
• Manufacturability
• Tsys with/without cooling
• Low cost/high reliability
• Developments
• ATA, Cornell, Chalmers, JPL, MeerKAT

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Technical Challenges - Array Data Processor

• Large N and N2
• Major cost driver
• Massive data transport, interconnect processing
• FX architecture almost certain
• Divide and conquer
• Packet switched fabric?
• FPGAs, ASICs multi-core processors
• Developments
• CASPER (IBOB-2), eVLA, 2-PAD,etc

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Technical Challenges - Computing

• Large N and N2
• Major cost driver
• Not only imaging
• Pulsars Transients
• Parallel reconfigurable computing
• Developments
• Probably not enough

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Complementarity / Innovation

• Aperture Arrays
• What is the transition frequency?
• Is there frequency overlap?
• Implications for lower diameter limit
• PAFs (upgrade path)
• f/D optical configuration
• Mechanical requirements
• High frequencies (lt 15 GHz)
• Multiple feeds - mechanical requirements
• Pointing and surface accuracy from day one

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Generic Issues

• Homogeneous dish diameters across entire array?
• Station Beam-forming?
• Configuration
• Flexibility/scalability/ease-of-use/cost trades
• Data Spigots
• Phased implementation
• Practical issues
• Science development