Presentation on theme: "Narrabri AM Meeting, 4 July 2001 Molonglo SKA Prototyping and MNRF Molonglo AUSTRALIA Brisbane Darwin Perth Canberra Hobart Adelaide Melbourne Sydney +"— Presentation transcript:
Narrabri AM Meeting, 4 July 2001 Molonglo SKA Prototyping and MNRF Molonglo AUSTRALIA Brisbane Darwin Perth Canberra Hobart Adelaide Melbourne Sydney +
Narrabri AM Meeting, 4 July 2001 Research Team: Anne Green 1, John Bunton 2, Duncan Campbell-Wilson 1, Lawrence Cram 1, Ralph Davison 1, Dick Hunstead 1, Daniel “Mitch” Mitchell 1,3, Andrew Parfitt 2, Elaine Sadler 1, George “Ñima” Warr 1,3  School of Physics, University of Sydney  Telecommunications and Industrial Physics, CSIRO  Australia Telescope National Facility, CSIRO Molonglo SKA Prototyping and MNRF
Narrabri AM Meeting, 4 July 2001 What is the SKA? The next generation radio telescope The Square Kilometre Array radio telescope: Large collecting area for high sensitivity (1 km 2 ) Array elements (stations) distributed over a wide area for high resolution (~4000 km) For good uv plane coverage, stations can’t be too sparse
Narrabri AM Meeting, 4 July 2001 Radio telescope sensitivity increasing logarithmically with time
Narrabri AM Meeting, 4 July 2001 SKA will provide higher sensitivity and resolution HST VLA SKA
Narrabri AM Meeting, 4 July 2001 Radio frequency interference (RFI) must be excised to get high sensitivity
Narrabri AM Meeting, 4 July 2001 For high resolution array stations are distributed across a continent
Narrabri AM Meeting, 4 July 2001 Phased array (Netherlands) 1000km (Courtesy NFRA)
Narrabri AM Meeting, 4 July 2001 Luneberg Lens (ATNF)
Narrabri AM Meeting, 4 July 2001 Luneberg Lens Focusing Action (ATNF)
Narrabri AM Meeting, 4 July 2001 Parabolic Reflector Array (SETI Institute, USA)
Narrabri AM Meeting, 4 July 2001 Aerostatically mounted receiver above Large Adaptive Reflector (Canada)
Narrabri AM Meeting, 4 July 2001 Large [Arecibo-like] Reflectors (China)
Narrabri AM Meeting, 4 July 2001 Cylindrical Parabolic Collector Molonglo (USyd, ATNF, CSIRO) Molonglo AUSTRALIA Brisbane Darwin Perth Canberra Hobart Adelaide Melbourne Sydney +
Narrabri AM Meeting, 4 July 2001 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 m 2 (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 Target Specifications Parameter1420 MHz300 MHz Frequency Coverage300–1420 MHz Bandwidth250 MHz Resolution (δ < -30°)26" x 26" csc|δ|123" x 123" csc|δ| Imaging field of view1.5° x 1.5° csc|δ|7.7° x 7.7° csc|δ| UV coverageFully sampled T sys < 50K< 150K System noise (1σ) 12 hr: 8 min: 11 μJy/beam 100 μJy/beam 33 μJy/beam 300 μJy/beam PolarisationDual Linear CorrelatorI and Q (Full Stokes at 125 MHz bandwidth) Frequency resolution120–1 kHz (FXF mode: 240 Hz) Independent fanbeam1.3’ x 1.5°6.2’ x 7.7° Independent fanbeam offset±6°±6°±27° Sky accessible in < 1 s180 deg deg 2
Narrabri AM Meeting, 4 July 2001 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 0.5. Will be able to detect a bright spiral galaxy (2.5 x solar masses of HI, V=200 km/s) at z=0.1 in 12 hours.
Narrabri AM Meeting, 4 July 2001 Selection of high-z radio galaxies by radio spectral index de Breuck (PhD 2000) - ultra-steep radio spectra ( < -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 deg 2 ) - we will be >5 times more sensitive and can use detailed radio spectra.
Narrabri AM Meeting, 4 July 2001 Molonglo able to measure evolution of HI mass function over z=0.03 to 0.26 log 10 M lim (HI) (M ⊙ ) (10 x 12 hr) Molonglo (12 hr) HIPASS (8 min) Galaxy with velocity width V = 200 km/s 1.7 deg 2 field H 0 = 50 km/s/Mpc, q 0 = 0.5
Narrabri AM Meeting, 4 July 2001 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 deg 2 accessible around main beam. Real time dedispersion. Pulsar and SETI Searches (optional 64 fanbeam system) Fast high sensitivity search.
Narrabri AM Meeting, 4 July 2001 Molonglo continuous uv coverage produces excellent image quality
Narrabri AM Meeting, 4 July 2001 Molonglo Continuum Confusion (10 beams/source) at δ = 60° Bock et al 1999 SUMSS 843 MHz Rengelink et al 1997 WENSS 325 MHz Wall MHz beam size: 43” x 43” csc| | beam size: 112” x 112” csc| | beam size: 26” x 26” csc| |
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
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 deg 2 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 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
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 m 2 ). 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. MD=Meridian Distance Geometry
Narrabri AM Meeting, 4 July 2001 x focus Molonglo parabola design accurate to > 1400 MHz 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. Piecewise linear fit to parabola shape
Narrabri AM Meeting, 4 July 2001 Original 408 MHz mesh needs replacing for operation above ~1 GHz Original mesh designed for 408 MHz (12mm NS x 25mm EW) 1420 MHz NS ~75K ground leakage 843 MHz NS
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 Beam Shape Distance (m) Patch positions on reflectors Synthesised 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.
Narrabri AM Meeting, 4 July 2001 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 Wide band ambient temperature low noise amplifiers required ~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 50 input impedance) Good starting point for migration to MMIC design Gain Frequency (MHz) |S| (dB) Output Match S 22 Input Match S 11 Prototype design for MHz HEMT based LNA (Ralph Davison)
Narrabri AM Meeting, 4 July 2001 Beamformer and Correlator 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 Beamforming and Digital Filterbanks for one of 44 bays
Narrabri AM Meeting, 4 July 2001 RFI at Molonglo MHz (Measured 25 June 2001) GSM VHF TV UHF TV
Narrabri AM Meeting, 4 July 2001 Molonglo SKA Prototype (Operating by ) 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 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