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Dual Polarisation All Digital Aperture Array Danny Price, University of Oxford CASPER Workshop 2009, Cape Town SA A 2-PAD Correlator, Holography, and Direct.

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Presentation on theme: "Dual Polarisation All Digital Aperture Array Danny Price, University of Oxford CASPER Workshop 2009, Cape Town SA A 2-PAD Correlator, Holography, and Direct."— Presentation transcript:

1 Dual Polarisation All Digital Aperture Array Danny Price, University of Oxford CASPER Workshop 2009, Cape Town SA A 2-PAD Correlator, Holography, and Direct Imaging

2 danny.price@astro.ox.ac.uk Introduction Danny Price Direct imaging correlators 2-PAD Correlator Holography

3 danny.price@astro.ox.ac.uk Part I: The 2-PAD Correlator Danny Price 2-PAD Correlator

4 danny.price@astro.ox.ac.uk 2-PAD Digital Backend Danny Price

5 danny.price@astro.ox.ac.uk Adding a correlator  Why tack on a correlator?  A1: Engineering challenge  A2: Two element interferometer  A3: Tile level calibration  A4: Holography experiment  Station level calibration  What sort of correlator?  2-element, 2-polarisation (full stokes)  FX correlator  Freq range? Bandwidth?  Pocket Correlator  Griffin Foster  Would like help with this here in Cape Town! Danny Price Image: Ant Holloway

6 danny.price@astro.ox.ac.uk Part II: A Holography Primer Danny Price 2-PAD Correlator Holography

7 danny.price@astro.ox.ac.uk Holography Primer Rectangle FunctionSinc Function Danny Price F.T.

8 danny.price@astro.ox.ac.uk Holography Primer Danny Price Reflector Antenna Horn Antenna

9 danny.price@astro.ox.ac.uk Holography Primer Danny Price Reflector Antenna Horn Antenna

10 danny.price@astro.ox.ac.uk Holography Primer Danny Price Aperture IlluminationF.F. Electric Field Pattern Radiation Power Pattern F.T. |F| 2

11 danny.price@astro.ox.ac.uk Holography Primer Danny Price Aperture IlluminationF.F. Electric Field Pattern Radiation Power Pattern F.T. |F| 2

12 danny.price@astro.ox.ac.uk 2-PAD Measurements Danny Price Aperture IlluminationF.F. Electric Field Pattern Radiation Power Pattern Photo: Ant Holloway

13 danny.price@astro.ox.ac.uk Dish Holography Danny Price Charles E. Mayer et. al., A holographic surface measurement of the Texas 4.9m antenna at 86GHz, 1983

14 danny.price@astro.ox.ac.uk Dish Holography Danny Price J. Baars et. al., Near-Field Radio Holography of Large Reflector Antennas, 2007

15 danny.price@astro.ox.ac.uk Aperture Array Holography  Why would we want a AA hologram?  A1: Measuring 2-PAD beam pattern  A2: Calibration  A3: Direct Imaging Correlator  Can we get a good enough hologram to calibrate 2-PAD?  A: Not sure yet – but if we have the beam pattern, it’s a simple FT to see the aperture Danny Price

16 danny.price@astro.ox.ac.uk Holography: Method Danny Price s t

17 danny.price@astro.ox.ac.uk Holography: Method Danny Price

18 danny.price@astro.ox.ac.uk Part III: Direct Imaging Danny Price Direct imaging correlators 2-PAD Correlator Holography

19 danny.price@astro.ox.ac.uk Direct Imaging Correlators  Direct imaging correlators do a spatial Fourier Transform, instead of electric field FT (FX / XF).  Rarely used because:  Antennas must be in a grid  Images produced suck  Calibration is hard  Individual visibilities are never formed => deconvolution is hard  Largest implementation is an 8x8 array at Waseda Uni, Japan (Dashido 2000). Danny Price Image: Ian Heywood

20 danny.price@astro.ox.ac.uk Direct Imaging Correlators  Morales shows that holographic data can drastically improve direct imaging correlators (2008):  Antennas must be in a grid  Images produced suck  Calibration is ??? hard  Individual visibilities are never formed Danny Price M. Morales, Enabling next generation dark energy and epoch of reionisation radio observatories with the MOFF correlator, 2008 Image: Ian Heywood

21 danny.price@astro.ox.ac.uk Direct Imaging Correlators  Measure Electric field  Weight by noise & grid using holography  Spatial Fourier Transform  Square & integrate to produce an image Danny Price Weight by noise Grid by holography Fourier Transform

22 danny.price@astro.ox.ac.uk Direct Imaging Correlators Danny Price

23 danny.price@astro.ox.ac.uk Conclusion Danny Price Direct imaging correlators 2-PAD Correlator Holography

24 danny.price@astro.ox.ac.uk Acknowledgements  Sascha Schediwy, Richard Armstrong, Kris Zarb-Adami, Jack Hickish, and Mike Jones  2-PAD team  Oxford  Cambridge  Manchester  Pre-emptive acknowledgements  CASPER Workshop 2009 attendees! Danny Price

25 danny.price@astro.ox.ac.uk Supplementary Material Danny Price

26 danny.price@astro.ox.ac.uk What is 2-PAD?  The purpose of 2-PAD is to design and implement a Dual Polarisation All Digital Phased Array for radio astronomy. In particular, 2-PAD aims to show the feasibility of ultra- wideband digital beamforming for radio astronomy purposes.  2-PAD is designed as a sandbox for testing different digital beamforming algorithms for radio astronomy. As such, the 2- PAD team is undertaking a variety of different approaches to digitisation, channelisation and beamforming.  CASPER beamforming approach headed by Richard Armstrong of The University of Oxford, DAQ card / offline / supercomputer based beamformer approach headed by The University of Manchester. Danny Price

27 danny.price@astro.ox.ac.uk OSKAR Simulator Danny Price Radiation Power PatternAperture Array http://wiki.oerc.ox.ac.uk/oskar

28 danny.price@astro.ox.ac.uk MOFF Maths Danny Price

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