Square-Kilometre Array

The Next Generation Radio Telescopehttp://www.atnf.csiro.au/SKA

Dr Peter J Hall

Australia Telescope National Facility

CSIRO SKA Program Leader

Presentation Outline

Radio astronomy and radio telescopes Motivation for building the SKA SKA concept and design goals

– key characteristics

Ideas for SKA realization– reflectors, arrays, lenses, signal processing

– interference mitigation

– site selection

Design and technology challenges Australian and international aspects of the SKA project

Radio Astronomy

Begun in 1930s by Karl Jansky - a Bell Labs communications engineer

Developed in 1940s by Grote Reber, a US radio engineer and radio amateur

Became respectable in late 1940s. Australia was an early player and has remained a world leader

Has provided insight into the most fundamental questions, e.g.

– 3 K big bang background radiation (communications engineers again)

– general relativity (binary pulsars) Gives access to physical conditions unattainable in labs Australia is good at astronomy, and RA in particular

– DISR impact studies

Radio Astronomy

RA derives information about the Universe from the study of natural radiation in the range ~ 10 MHz - 1000 GHz

Radio telescopes use the combination of an antenna and receiver to form a radiometer - a device for measuring the radiation temperature of a distant region of space viewed by the antenna beam

The received radiation may be continuum (broadband noise) or spectral line (“quasi-cw”) in character; variation on timescales of milliseconds to years may be involved

The measured temperature may or may not be the physical temperature of the region, depending on whether the emission is thermal or non-thermal

Radio Telescopes

Can be:– single continuous aperture (e.g. parabolic dish)

» focussing (wavefront delay) done optically

– synthesized aperture (e.g. array)» focussing done using time delay electronics

» can make huge effective aperture

» mathematically manipulate wave interference patterns between array elements to simulate continuous aperture

Sensitivity depends on total collecting area of aperture Angular resolution depends on linear extent of aperture (micro-

arcsecond attainable) Typically use very low-noise receivers (e.g. cryogenically cooled)

Computer

Dishes and Arrays

$$$ (computers)$$$

(Steel)

New paradigm: wavefront sensors and software replace steel

Physical Aperture

Synthesized Aperture

Major ATNF Radio Telescopes

64 m Parkes dish; 6 x 22 m AT Compact Array; both upgraded substantially to maintain international competitiveness

Radio Images Using the ATCA

SN1987a

NGC1808

PKS2356-61

Radio Telescopes of the Future HEMT receivers

– Wide-band, cheap, small and reliable– Need to build low-noise systems with many elements

Focal planes arrays– N beams => N-fold increase in telescope speed (and data rate!)– Greatly improve calibration schemes and imaging dynamic range – Synthesised beams and illumination patterns to overcome problems of feed

packing

Interference rejection– Adaptive nulling and RFI cancelling can work in single dishes and arrays

More computing capacity– Computing power doubles every 18 months (Moore’s Law)– Era of software-defined radio telescopes is upon us

Square Kilometer Array - Why?

Current large telescope technology dates from 1960/70’s

» VLA total area ~ 104 m2

Era of facilities upgrades approaching its end

Large increase in sensitivity is needed (100x), telescopes not receiver noise

limited ==> 1 km2 collecting area » epoch of first stars and galaxies» major advance in many other areas of astronomy (and hence physics)

New challenges: » cost ($US600 m cf ~ $US50 m for ATCA)» frequency coverage» man-made interference» completion by ~2010

Technology shift will be required

Radio Telescope Sensitivity

GMRT

Reber

Dwingeloo

Jodrell BankParkes

Arecibo

BonnWSRT

VLAAT

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1940 1950 1960 1970 1980 1990 2000

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SKA

Core Issue

HST VLA

Solution

HST SKA

“Dark Ages”- before the stars ? Square-Kilometre Array

COBE satelliteNASA

“Primordial soup” - matter and energy

radio

Early galaxies- stars light up

Hubble Space TelescopeNASA / ESA

light

Astronomy Beyond the Light

SKA: Selected “Other” Astronomy

Active Galactic Nuclei

– does every ‘normal’ galaxy contain a black hole? Magnetic fields

– Faraday rotation studies of Milky Way, intergalactic medium and nearby galaxies Radio emission from hot and cool stars

– including imaging surfaces and atmospheres of giant stars Radio after-glows of gamma-ray bursts

– merger of a neutron star pair? Pulsars

– first demonstrated existence of extra-solar planets and gravitational waves; explicit demonstrations of general relativity

– future use in timing standards; interplanetary navigation; cosmological background of gravity waves

Deep space network tracking; SETI

SKA: The Concept One square km radio telescope (SKA) in 2010

– 2005 technology choice– 2007 construction– 2012 operations

Frequency range 0.3 - 12 GHz (minimum) Sensitivity 100 x VLA

– need ~ 68 dB K-1 at 1.4 GHz Multibeam essential at lower frequencies Need innovative design to reduce cost International funding unlikely to exceed $US600m

– 106 sq metre => ~$500 / sq metre» cf VLA $10,000 / sq metre

» GMRT $1,000 / sq metre

SKA Top-Level Specifications

Parameter Design GoalSensitivity Effective Area/System Temperature =

2 x 104 m2K-1

(about 68 dB K-1 at 1.4 GHz)Frequency range f = 0.2 to GHzNumber of simultaneous beams ~ 100Field of view 1 degree square at 1.4 GHzAngular resolution 0.1 arcsecond at 1.4 GHzInstantaneous bandwidth 0.5 + (f/5) GHzNumber of spectral channels 104

Number of simultaneous bands 2Polarization purity dB couplingSynthesized image dynamic range 106 at 1.4 GHz

Sky Key CharacteristicsOperating Frequency

SKA Key CharacteristicsField of View

HST FOV

1kT 20cm

1kT 6cm

mmA FOV

20 M

pc

at z

= 0

.3

SKA Key CharacteristicsConfiguration

200 km

20 km

Array Station

SKA Key CharacteristicsMultibeaming

4

8

12

16Synthesized beams

Station antenna patterns

Element antenna pattern

NFRA 1998

SKA - Multiple Station Concept

1000km(Courtesy NFRA)

Large Reflector SKA

Need revolution in construction technique before conventional large steerable dishes could be used

Chinese have suggested multiple Arecibo (‘holes in ground’) approach

SKA - Large Adaptive Reflector

Tile Array SKA

Luneburg Lens SKA

Luneburg Lens Focussing

Plane waves incident from left 1 m diameter lens, 2 GHz

radiation Classical Luneburg - focus on

surface

(Image courtesy Dr Andrew Parfitt, CTIP)

Luneburg Lens - The Loss Issue

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Noise Temperature Increase vs Lens Loss at Tphysical

= 290 KN

ois

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pe

ratu

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K)

Insertion Loss (dB)

Luneburg Lens - Alternative SKA Implementation

SETI Institute - 1hT

SKA Signal Processing - Reality Check

Can we expect to be able to process the signals from an array as vast as the SKA?

Look at the growth in computation power per unit (area, dollar…)– familiar as Moore’s Law

Moore’s Law - Astronomical Correlators

Correlator Performance vs Time

VLA?VLBA

ATNobeyama

VLAWRST

Fleurs

Mills Cross

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1950 1960 1970 1980 1990 2000 2010 2020

Ope

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Year

(Roughly doubles every two years)

SKA Signal Processing - Rough Guide

To correlate 106 antennas, over a 500 MHz bandwidth, with 104 frequency channels needs ~ 1012 Giga ops/sec

In 2010 astronomical correlators will be capable of ~107 Giga ops/sec– must aggregate SKA antennas prior to correlation– can only correlate ~4000 ‘elements’– with 100 stations, each station can have ~40 clusters of antennas– with 400 Luneburg Lens station, combine 10 lenses per cluster

If we wait until 2020, can reduce aggregation by ~3 – but only if Moore’s Law holds!

SKA - Interference Mitigation

Why?– SKA needs to observe outside (small) designated astronomy bands to

meet its scientific objectives

– SKA sensitivity is unprecedented (~100 times VLA)» each beam ~ 10Jy in 1 sec OR ~ -265 dBW/m2/Hz (128 MHz continuum

bandwidth)

– terrestial transmissions will be a problem for all but a few sites on Earth

– satellite transmissions are now globally pervasive (intentional constellation coverage for many LEOs)

How?– No single IM solution; need a hierarchy of techniques starting with

telescope site and environment, and ending with astronomy data processing

Terrestrial Interference

FORTÉ satellite: 131 MHz

Global InterferenceFrom The Sky - An Example

IRIDIUM satellite:measured 1998

ITU frequency allocation to Radio Astronomy

Signal levels of brightest*celestial radio sources

These peaks also change frequencyas the satellite moves across the sky

* Signals from early Universe are 100 billion times weaker

MHz

ITU permittedaverage levelS

ign

al

stre

ngt

h

SKA Interference Mitigation Essentials

Effective Robust Versatile: different observing modes, different

techniques (or different emphases in hierarchy)– e.g. snapshot versus synthesis imaging modes; pulsar modes

Low toxicity– removing the interference must not ruin the astronomy data, nor

turn easy-to-identify spurious signals into hard-to-identify artifacts

– bear in mind the imaging dynamic range needed in the SKA is >106 so uncorrected fiddling with imaging beams may be disastrous

SKA Interference Mitigation Hierarchy

Location of instrument (esp. central cluster), and legislated or regulated radio quiet zone

Array configuration (use power of correlation processing for as much critical science as possible)

Choice of concentrators and feeds Design of (cheap) high-intercept MMIC low-noise amplifiers Placement of RF/IF filters for high-level, fixed frequency RFI (e.g.

photonic fibre filters) “High” resolution quantizers and first-level digital filters DSP adaptive techniques (exploiting SKA buffer?) New image and time-domain processing techniques

Practical Interference Mitigation

AT Compact Array data Russian GLONASS satellite +

two frequency markers + astronomy signal in passband

Off-line digital adaptive filtering by Steve Ellingson, Electrosciences Lab OSU

On-line (real-time) realizations possible

Much synergy with military and commercial users

SKA Site Selection

Australia - Terrestial Transmitters

WA Site Search Area

Australian SKA Configuration?

SKA Critical Design Challenges

Wide bandwidth– antenna element type; use of true time delay phasing

Sensitivity– how to maintain effective area of antennas with frequency variation

Cost– need highly-integrated, easily manufactured systems

Interference mitigation– telescope site, adaptive RF, photonic and digital techniques

Calibration– 106 dynamic range; good polarization purity; both in presence of adaptive beaming!

Upgrade path– expensive infrastructure must last well; need to follow Moore’s Law (or equiv.)

Operations – robust; maintainable; advanced power generation and management

SKA Critical Technologies

Antennas & feeds– wideband, multi-beaming, easily manufactured, cheap– specific CSIRO challenge to make a cheap Luneburg Lens

RF front-ends– low-noise, ambient temperature, very highly integrated

Signal transmission and distribution– wideband analog or digital station links– need cost breakthrough in opto-electronic modulators– probably incorporate photonic signal processing in analog stages

Digital signal processing– for correlators, interference mitigation

Software– the SKA will be largely a “software radio” telescope

SKA - Current Australian Innovation

Antennas and arrays (e.g. Luneburg Lens, feed arrays) Highly-integrated (GaAs or InP MMIC) receivers Radio-frequency interference mitigation

– Adaptive (“smart”) antennas

– Robust receivers

– Software radio Photonics

– Fibre communications (GHz analog and digital)

– SKA connectivity and signal delay (wavelength division multiplexing)

– Active and passive fibre signal processing (e.g. bandstop filters)

– Ultra-wideband A-D Converters (15 GHz) Advanced synthesis imaging techniques

SKA - Benefits to Australia

CIE report for DISR (**DISR disclaimer)– distinguishes between participating and participating and hosting– examines quantified and unquantified benefits and costs

Quantified costs and benefits (QC&B)– R&D expenditure; operating expenditure; human capital; construction

expenditure; tourism benefits

Unquantified costs and benefits (UC&B)– development contracts; new IP; scientific knowledge; construction contracts;

HR & technology spinoffs; national prestige; community awareness of science and engineering

Bottom line for break-even– Participating: UC&B > $62 m (quantified cost ~ $72 m)

– Participating and hosting UC&B > $44 m (quantified cost ~ $81 m)

CSIRO Technology:Communications Antennas

Astronomy

Communications

Benefit / cost ~ 2(real estimate)

Achieving the Vision - International Collaboration

To build facilities which no single nation can afford Broaden knowledge base and provide cross fertilisation Joint URSI - IAU working group Endorsed by the OECD Megascience forum International MOU for technology study program

– Netherlands Australia

– China India

– Canada U.S.

– UK

Funding Distribution

Australia$50M

Asia$50M

Europe$250M

Nth. America$250M

Total cost $US600M

Australian Funding Profile

New funds

CSIRO

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Strategic research

Prototype Construction Operations

Close existing facility

Summary

SKA is a scientific necessity if we are to understand critical phases in the evolution of the universe

It will have wide general application in all areas of astronomy

The scale of the telescope requires new design concepts and enabling technologies

Australia, and CSIRO, are well-placed to continue a leading role in the project

There are many opportunities for commercial involvement - astronomers are demanding (but harmless) customers

Updates at http://www.atnf.csiro.au/SKA