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Дата изменения: Mon Feb 16 02:35:15 2004
Дата индексирования: Sun Sep 7 02:30:24 2008
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A Multi-Fielding SKA
Peter Hall & Aaron Chippendale Cape Town, January 2004

Background
Only AA & LL offer independent multi-fielding at whole-array sensitivity ("area re-use")
"Multi-fielding" means widely separable FOVs

Multi-fielding offers important science and operational gains at all frequencies Cost studies show that only small-M (1 Primary gain to science is via operational parallelism
» Greater access to instrument, ability to undertake extended programs, dedicated transient and SETI modes, greater ability to develop new observational modes and explore new phase space, enhanced diagnostics and calibration, .....

SKA lifetime will extend to 2050
Frequencies above 2 GHz will require a flux concentrator If multi-fielding is to be feasible in 1st half of century, need to pursue an omni concentrator

In a LL SKA implementation antenna cost is minimum with small lenses
A r2 ; dielectric volume r3 Small lenses lead to same electronics-dominated regime as AA
» Evolutionary path with advancing technology (e.g. DSP)

Multi-fielding requirement is a primary driver for SKA antenna technology
But studying the parallelism made possible by multi-fielding is instructive in any SKA system design
» E.g. ensures due weight to switching and sub-array modes in dish-based designs

Multiple FOVs Advantages

The AA+LL Concept

The Concept Some Detail
3-band AA + 27,600 LL (3.5 m dia)
300 stations, 4 FOVs over entire band 0.1-22 GHz, highly flexible signal transport and DSP simultaneous AA and LL use AA and LL components add in 1-1.5 GHz band
» Could overlap 0.5-1.5 GHz

Primary FOV at 1.4 GHz is about 14 deg2
» x 4 ~ 60 deg2 (cf CR ~24 deg2) · With 0.8 GHz BW, process about Ѕ FOV in 2015

2 x linear poln, 3000+ km baselines 8 FOVs on AA may be possible Closer to "software telescope" than most concepts
» Substantial instrument evolution possible

Save 80% of dielectric relative to 2003 LL proposal (7m lenses) Better Tsys due to lower lens loss and better receivers

AA+LL Costing
Component cost = USD 1.1B
Plus civil, infrastructure and software total cost USD 1.4 B

Division of cost:

Steel now dominates LL cost; need smart feed positioning! (May allow more LL area)

A Week in 2018

Parallelism & Discovery
Paydarfar and Schwartz algorithm for discovery
Slow down to explore
» Discovery facilitated by unhurried approach

Pursue quality for its own sake
» Time spent refining methods and design is almost always rewarded

Look at the raw data (Read, but not too much; cultivate smart friends)

Science, 6 April 2001

Harwitt notes
Discovery favoured when observer has the chance to trust his/her instrument more than current theories Discovery favoured when a new instrument substantially extends the parameter space AND when expert users have large blocks of time available to fully extend the instrument
» Normally argues against immediate national/international facility use BUT with area re-use one can have BOTH modes in the SKA

A figure-of-merit for an SKA design should involve a product of performance gain and instrument access
Both can make the SKA unique

Major Aust Contributions to Wider SKA
Largest Southern Hemisphere radio telescopes
Lead-in science for SKA, platform for testing new techniques, ...

Strong systems design tradition
Astronomers and engineers have worked closely Important in emerging areas such as SKA int mit, calibration, ...

Antenna and feed design and metrology
E.g. existing/previous AA tile, DSN, LL, ...

Integrated RF systems (to > 100 GHz)
Uncooled wholly integrated rx being developed (CR, EMBRACE, ....)

Leading-edge signal processing architectures and components
E.g. scaleable F/X correlator, 10 GHz ADC, 15 GHz analog multiplier, ...

Supercomputer-based simulation and visualization Advanced imaging techniques Infrastructure and construction engineering
History of commercial antenna fabrication for international clients Strong international project management sector

Substantial experience in site selection practices and related aspects
E.g. radio quiet reserves