1. Molonglo SKA Prototyping and MNRF
AUSTRALIA
Brisbane
Darwin
Perth
Canberra
Hobart
Adelaide
Melbourne
Sydney +
Narrabri AM Meeting, 4 July 2001

2. Molonglo SKA Prototyping and MNRF
Research Team:
Anne Green1, John Bunton2, Duncan Campbell-Wilson1, Lawrence Cram1, Ralph Davison1, Dick Hunstead1, Daniel “Mitch” Mitchell1,3, Andrew Parfitt2, Elaine Sadler1, George “Ñima” Warr1,3
[1] School of Physics, University of Sydney
[2] Telecommunications and Industrial Physics, CSIRO
[3] Australia Telescope National Facility, CSIRO
Narrabri AM Meeting, 4 July 2001

3. What is the SKA? The next generation radio telescope
The Square Kilometre Array radio telescope:
Large collecting area for high sensitivity (1 km2)
Array elements (stations) distributed over a wide area for high resolution (~4000 km)
For good uv plane coverage, stations can’t be too sparse
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4. Radio telescope sensitivity increasing logarithmically with time
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5. SKA will provide higher sensitivity and resolution
HST
VLA
SKA
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Radio frequency interference (RFI) must be excised to get high sensitivity
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7. For high resolution array stations are distributed across a continent
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8. Phased array (Netherlands)
1000km
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(Courtesy NFRA)

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Luneberg Lens (ATNF)
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10. Luneberg Lens Focusing Action (ATNF)
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11. Parabolic Reflector Array (SETI Institute, USA)
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Aerostatically mounted receiver above Large Adaptive Reflector (Canada)
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13. Large [Arecibo-like] Reflectors (China)
Narrabri AM Meeting, 4 July 2001

14. Cylindrical Parabolic Collector Molonglo (USyd, ATNF, CSIRO)
AUSTRALIA
Brisbane
Darwin
Perth
Canberra
Hobart
Adelaide
Melbourne
Sydney +
Narrabri AM Meeting, 4 July 2001

15. Molonglo SKA Prototyping and MNRF. Overview
Molonglo telescope is an E-W array of two collinear cylindrical paraboloids.
total length of 1.6 km (2 x 800m with 15 m gap between them).
Collecting area 18,000 m2 (largest in the Southern Hemisphere). 
We propose to equip the telescope with new feeds, low-noise amplifiers, digital filterbanks and FX correlator as an SKA prototype with continuous frequency coverage in multibeam mode from MHz. 
Allows development and testing of several new technologies.
Provides a sensitive instrument for exploring the distant universe.
Funding for this project is currently being sought from the Australian Government's Major National Research Facilities (MNRF) program.
The Molonglo Telescope has been operated by the University of Sydney since Major achievements include the Molonglo Reference Catalogue (MRC; 408 MHz) and a sensitive all-sky imaging survey, Sydney University Molonglo Sky Survey (SUMSS; 843 MHz) that will be completed in 2003.
Narrabri AM Meeting, 4 July 2001

16. Target Specifications
Parameter
1420 MHz
300 MHz
Frequency Coverage
300–1420 MHz
Bandwidth
250 MHz
Resolution (δ < -30°)
26" x 26" csc|δ|
123" x 123" csc|δ|
Imaging field of view
1.5° x 1.5° csc|δ|
7.7° x 7.7° csc|δ|
UV coverage
Fully sampled
Tsys
< 50K
< 150K
System noise (1σ) hr: 8 min:
11 μJy/beam 100 μJy/beam
33 μJy/beam 300 μJy/beam
Polarisation
Dual Linear
Correlator
I and Q (Full Stokes at 125 MHz bandwidth)
Frequency resolution
120–1 kHz (FXF mode: 240 Hz)
Independent fanbeam
1.3’ x 1.5°
6.2’ x 7.7°
Independent fanbeam offset
±6°
±27°
Sky accessible in < 1 s
180 deg2
1000 deg2
Narrabri AM Meeting, 4 July 2001

17. Molonglo SKA Prototyping and MNRF Main science goals:
Low-frequency radio spectrometry ( MHz)
Selection of objects via their radio spectral shape, e.g. candidate high-redshift (z>3) galaxies with ultra-steep radio spectra (de Breuck et al. 2000), which allow us to study the formation of galaxies and massive black holes.
Redshifted HI ( MHz)
HI in absorption against bright continuum sources over a wide redshift range (z=0 to 3).
HI in emission - evolution of the HI mass function from z=0 to Will be able to detect a bright spiral galaxy (2.5 x 1010 solar masses of HI, DV=200 km/s) at z=0.1 in 12 hours.
Narrabri AM Meeting, 4 July 2001

18. Selection of high-z radio galaxies by radio spectral index
de Breuck (PhD 2000) - ultra-steep radio spectra (a < -1.3) can select (some) high-z galaxies
K magnitude is a good initial redshift estimator
BUT two-point spectral index is crude (finds only ~1 candidate per deg2) - we will be >5 times more sensitive and can use detailed radio spectra.
Narrabri AM Meeting, 4 July 2001

19. Molonglo able to measure evolution of HI mass function over z=0
Molonglo able to measure evolution of HI mass function over z=0.03 to 0.26
HIPASS (8 min)
Molonglo (12 hr)
H0 = 50 km/s/Mpc, q0 = 0.5
(10 x 12 hr)
1.7 deg2 field
log10 Mlim (HI) (M⊙)
Galaxy with velocity width DV = 200 km/s
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Science Goals ctd…
Low-frequency Galactic recombination lines
Recombination lines of carbon and hydrogen can be used to probe the partially-ionized ISM and constrain the physical conditions (Anantharamaiah & Kantharia 1999).
Gamma Ray Bursters
Electronic beam steering gives 5% chance of monitoring instantaneously on alert.
Concurrent Pulsars and Source Flux Monitoring
18 to 400 deg2 accessible around main beam.
Real time dedispersion.
Pulsar and SETI Searches (optional 64 fanbeam system)
Fast high sensitivity search.
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21. Molonglo continuous uv coverage produces excellent image quality
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22. Molonglo Continuum Confusion (10 beams/source) at δ = -60°
Bock et al 1999
SUMSS 843 MHz
Rengelink et al 1997
WENSS 325 MHz
Wall 1994
1420 MHz
beam size:
43” x 43” csc|d|
112” x 112” csc|d|
26” x 26” csc|d|
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23. Narrabri AM Meeting, 4 July 2001
SKA Technologies
Multibeaming
Wide instantaneous field of view
Digital Beamforming
FX Correlators
Frequency and Pointing Agility
Wideband linefeeds and LNAs
Cylindrical Antenna Prototype – in particular addressing
Polarisation purity
Beam variability/stability
Inter-antenna patch coupling
Adaptive Null steering and Adaptive Noise cancellation
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24. Narrabri AM Meeting, 4 July 2001
Observing Modes
Wide Field Imaging
Full integration over 12 hours or multiple snapshots.
Spectral Line Observations
FX mode 2048 channels, each kHz ( km/s).
FXF mode 1 or 2 channels with 768 complex lags.
Independent Fanbeam Observations
An independent fanbeam can be formed within ±6° (1420 MHz) or ±27° (300 MHz) of the imaging beam, e.g., for pulsar timing or flux monitoring.
Interleaved Observing [Rapid electronic changes (< 1 s) in frequency & meridian distance]
Frequency agility  spectral index determination.
Meridian angle agility  10,000 deg2 of sky accessible during routine 12h observations, e.g., source monitoring or calibration.
Optional digital beamformer with 64 fanbeams
Pulsar and SETI search observing.
Narrabri AM Meeting, 4 July 2001

25. Signal Path and Antenna Pattern
Cylindrical Parabolic Collectors
(Two collinear 778 m x 12 m)
MHz Feed and LNA
(7,400 feeds, 14,800 LNAs)
Delay line beamforming
(Over 9 feeds)
Analog to Digital Converter
(1,600 8 bit 250 MHz BW ADCs)
Digital delay beamforming
(80 10 m x 10 m patches)
Digital filterbank (160)
(Two 250 MHz/patch)
FX Correlator
(3,160 baselines, 2,048 channels)
Signal processing & storage
(imaging, spectrometer, searching...)
Independent fanbeam
(1 within 9 feed field of view)
Digital Beamformer
(64 fanbeams within imaging beam)
[Requires extra funding]
Single feed beam
Delay line beam
Independent fanbeam
Imaging beam
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26. Narrabri AM Meeting, 4 July 2001
Collector
The telescope’s collector consists of two cylindrical paraboloids, 778m x 12m, separated by 15m and aligned east-west (total area 18,000 m2).
The telescope is steered by mechanical rotation of the cylindrical paraboloids about their long axis, and by electronic delays of the feed elements along the arms. The resulting ‘alt-alt’ system can follow fields south of declination -30° for ±6 hours.
The original parabola shape was designed to be accurate for operation at 1.4 GHz. The reflecting mesh was designed for operation at 408 MHz and will need to be replaced for operation above ~1 GHz.
Geometry
MD=Meridian Distance
Narrabri AM Meeting, 4 July 2001

27. Molonglo parabola design accurate to > 1400 MHz
Piecewise linear fit to parabola shape
x focus
Flat mesh tied on supports at points shown
Mesh supported at 0.6 m (2 ft) intervals in x direction.
Each section gives the same error for a linear fit to a parabola.
Gives only 0.1 dB loss at 1420 MHz.
Narrabri AM Meeting, 4 July 2001

28. Original 408 MHz mesh needs replacing for operation above ~1 GHz
843 MHz NS
1420 MHz NS
~75K ground leakage
Original mesh designed for 408 MHz (12mm NS x 25mm EW)
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29. Narrabri AM Meeting, 4 July 2001
Resurfacing Issues
Wind loading
Pointing accuracy
Not a major issue if using a mesh rather than a solid surface.
No noticeable extra loading at Parkes after resurfacing (with porous surface).
Pointing accuracy degraded at ATCA in windy conditions and low elevations after replacing with solid surface. Possibly due to increased vacuum on lee side of dish.
Narrabri AM Meeting, 4 July 2001

30. Beam Shape
The synthesised beam shape for a possible configuration of antenna patches on the telescope is shown.
This configuration has a contiguous patch covering a third of the telescope area for forming 1.3’ beams for pulsar or SETI searches.
The remaining part of the telescope is more sparsely covered (with positions calculated from a simple grading function) to give good imaging resolution.
Synthesised Beam Shape
800
-800
Distance (m)
Patch positions on reflectors
Narrabri AM Meeting, 4 July 2001

31. Wide Band Feeds Required
Single feed covering MHz desirable
Vivaldi antenna array suitable?
ASTRON THEA operates over MHz
Highest performance at high frequencies. At lower frequencies:
Higher sky temperature
Increased source counts per steradian
Larger beam size
Narrabri AM Meeting, 4 July 2001

32. Wide band ambient temperature low noise amplifiers required
Prototype design for MHz HEMT based LNA (Ralph Davison)
Gain
300
1400
850
Frequency (MHz)
-30
-15 15 30 45
|S| (dB)
Output Match S22
Input Match S11
~20K noise temperature
Ambient temperature operation
Likely to be able to extend to operate over MHz
Design simplifications possible if higher input impedance from antenna (designed for 50W input impedance)
Good starting point for migration to MMIC design
Narrabri AM Meeting, 4 July 2001

33. Beamformer and Correlator
Beamforming and Digital Filterbanks for one of 44 bays
Analog delay line beamforming
Accuracy /4
Each polarisation
RF 0.3 to 1.4 GHz
LO 2.2 to 0.9 GHz
IF at 2.5 GHz
Quadrature baseband detection
Dual 250 MSamples/s 8-bit A/Ds generating a complex 250 MHz signal
Digital Beamforming
Fine delays accuracy /16
Delay corrects for average analog delay error
Arbitrary and time varying grading
Modifiable beam shape with meridian distance
Resources for adaptive null steering
250 MHz complex digital filterbanks
120 kHz frequency channels
Single FPGA implementation
Adaptive noise cancellation on a per channel basis
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34. RFI at Molonglo 200-1500 MHz (Measured 25 June 2001)
UHF TV
VHF TV
GSM
Narrabri AM Meeting, 4 July 2001

35. Molonglo SKA Prototype (Operating by 2004-2005)
New line feeds: prototypes for SKA cylindrical doublet antennas
New low-noise amplifiers
Resurface telescope to operate at higher frequency
Photonics for LO distribution, signal gathering and beam forming
Wide-band FX correlator
‘Software telescope’ - computerised control, beam forming and data acquisition
Automated remote operation, data pipeline
Result: MHz radio ‘spectrometer’ with >5 times increase in continuum sensitivity, high dynamic range, fully-sampled uv plane. New spectral-line capability for redshifted HI.
Narrabri AM Meeting, 4 July 2001

36. Narrabri AM Meeting, 4 July 2001
Summary
Science: Studies of the high-redshift universe (high-z galaxies, evolution of HI mass function)
Technology: prototype for SKA cylindrical antennas, software beamforming, high dynamic range observing with fully-sampled uv plane
Community use: New national facility that re-opens the radio spectrum below 1.4 GHz, operating by 2005 as a fully-automated remote observing telescope with a data reduction pipeline
Narrabri AM Meeting, 4 July 2001