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Advantages and Disadvantages of Sparse Aperture Arrays

Advantages and Disadvantages of Sparse Aperture Arrays. Fermilab: October 2009. Motivation and Contents. Sascha Schediwy: sws@astro.ox.ac.uk. http://2-pad.physics.ox.ac.uk. Introduce some of the concepts of mid-frequency, sparse aperture arrays

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Advantages and Disadvantages of Sparse Aperture Arrays

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  1. Advantages and Disadvantagesof Sparse Aperture Arrays Sascha Schediwy: sws@astro.ox.ac.uk Fermilab: October 2009

  2. Motivation and Contents Sascha Schediwy: sws@astro.ox.ac.uk http://2-pad.physics.ox.ac.uk • Introduce some of the concepts ofmid-frequency, sparse aperture arrays • Show that 2-PAD is the perfect test-bed for experimentally investigating these concepts • Aperture Array Review • Sparse Aperture Array Concepts • Effective Area • High-Gain Antenna Strategy • Instantaneous Field of View • Sky Coverage • Dynamic Range • Computational Complexity • 2-PAD Sparse Configuration Sascha Schediwy: sws@astro.ox.ac.uk Fermilab: October 2009

  3. Aperture Arrays Sascha Schediwy: sws@astro.ox.ac.uk http://2-pad.physics.ox.ac.uk Sascha Schediwy: sws@astro.ox.ac.uk Fermilab: October 2009

  4. Aperture Arrays +2 +1 0 -1 -2 -2 0 -1 0 0 0 +1 0 0 +2 Sascha Schediwy: sws@astro.ox.ac.uk http://2-pad.physics.ox.ac.uk beamformer Sascha Schediwy: sws@astro.ox.ac.uk Fermilab: October 2009

  5. Sparse Aperture Arrays • Dense: d ≤ λ/√2, Sparse: d > λ/√2 d Sascha Schediwy: sws@astro.ox.ac.uk Fermilab: October 2009

  6. Effective Area fc= 300MHz fc dense up to fc = 700MHz fc dense up to fc = 1000MHz Sascha Schediwy: sws@astro.ox.ac.uk http://2-pad.physics.ox.ac.uk • Dense: Aeff = λc2/2, Sparse: Aeff = λ2/2 • Critical frequency fc Effective Area per Element sparse limit [SKA Memo 100] Sascha Schediwy: sws@astro.ox.ac.uk Fermilab: October 2009

  7. High-Gain Antenna Strategy Sascha Schediwy: sws@astro.ox.ac.uk http://2-pad.physics.ox.ac.uk • “The total cost of aperture array is strongly correlated with number of receiver chains” • If each antenna element has more forward gain, you can use less antennas while still maintaining comparable effective area, but make drastic cost savings due to the reduction in receiver chains S = Aeff /TsysSSFoM = (Aeff /Tsys)2 ∙ FoV • Therefore maintain target SKA sensitivity and survey speed while decreasing cost [SKA Memo 100] Sascha Schediwy: sws@astro.ox.ac.uk Fermilab: October 2009

  8. Instantaneous Field of View • 60m Dish + Phased Array Feed • 120deg+10,000deg2+ • 18deg250deg2 • Fully Digital Dense A. Array • 120deg10,000deg2 • 18deg250deg2 • Hybrid Dense A. Array • 120deg10,000deg2 • 28deg 625deg2 • 18deg250deg2 • Sparse High Gain A. Array • 36deg1,000deg2 • 18deg250deg2 Sascha Schediwy: sws@astro.ox.ac.uk Fermilab: October 2009

  9. Overall Sky Coverage Sascha Schediwy: sws@astro.ox.ac.uk http://2-pad.physics.ox.ac.uk • Earth rotation gives full coverage in RA • Trick: 3-way 36° switching mechanism to get a 108° of declination • Karoo SKA site (SA) 30.5°S • Murchison SKA site (WA) 26.5°S Sascha Schediwy: sws@astro.ox.ac.uk Fermilab: October 2009

  10. Instantaneous Sky Coverage     Sascha Schediwy: sws@astro.ox.ac.uk http://2-pad.physics.ox.ac.uk • Which key science projects require pointing in opposite parts of the sky? • 1 – The Dark Ages • 2 – G. Evolution, Cosmology & Dark Energy • 3 – Cosmic Magnetism • 4 – GR using Pulsars & Black Holes • Search • 4a – Gravitational Waves • 4b – BH Spin • 4c – Theories of Gravity    • 5 – Cradle of Life • 5a – Proto-planetary Disks • 5b – Prebiotic Molecules • 5c – SETI  • 6 – Exploration of the Unknown Sascha Schediwy: sws@astro.ox.ac.uk Fermilab: October 2009

  11. Dynamic Range • Station beam pattern BeamPower Station Beam Pattern • Antenna separation: random (f > 1) dense (f < 1) nominal (f = 1) sparse (f > 1) Antenna Element Separation [SKA Memo 87] Sascha Schediwy: sws@astro.ox.ac.uk Fermilab: October 2009

  12. Computational Complexity • www.oerc.ox.ac.uk/research/oskar • For a constant processed FoV, the digital processing complexity increases as the square of the sparseness factor [SKA Memo 87] Sascha Schediwy: sws@astro.ox.ac.uk Fermilab: October 2009

  13. OSKAR Simulator Sascha Schediwy: sws@astro.ox.ac.uk http://2-pad.physics.ox.ac.uk Sascha Schediwy: sws@astro.ox.ac.uk Fermilab: October 2009

  14. 2-PAD Aperture Array Sascha Schediwy: sws@astro.ox.ac.uk http://2-pad.physics.ox.ac.uk • Dual-Polarisation All Digital Aperture Array • Dual Polarisation plug and play antennas • 4x4 antenna array • Various interchangeable antennas • 300-1000MHz RF range • Digital backend processing • Multi-FPGA boards, Multi-ASIC boards • 200MHz processed bandwidth • Multiple independent beams • No. of Beam vs. Bandwidth trade-off • Demonstrate upgrade path to the AAVP Sascha Schediwy: sws@astro.ox.ac.uk Fermilab: October 2009

  15. 2-PAD Aperture Array Sascha Schediwy: sws@astro.ox.ac.uk http://2-pad.physics.ox.ac.uk Sascha Schediwy: sws@astro.ox.ac.uk Fermilab: October 2009

  16. 2-PAD High Gain Antenna Sascha Schediwy: sws@astro.ox.ac.uk http://2-pad.physics.ox.ac.uk • Log-periodic dipole array (LPDA) antenna • Frequency range = 300-1000+ MHz Sascha Schediwy: sws@astro.ox.ac.uk Fermilab: October 2009

  17. 2-PAD High Gain Antenna Sascha Schediwy: sws@astro.ox.ac.uk http://2-pad.physics.ox.ac.uk • Beam-width = 34.5° (Field of View = 928deg2) • Gain = 13.2dBi (20.9x isotropic) Sascha Schediwy: sws@astro.ox.ac.uk Fermilab: October 2009

  18. ROACH Correlator Sascha Schediwy: sws@astro.ox.ac.uk http://2-pad.physics.ox.ac.uk Sascha Schediwy: sws@astro.ox.ac.uk Fermilab: October 2009

  19. Jodrell Bank RFI Sascha Schediwy: sws@astro.ox.ac.uk http://2-pad.physics.ox.ac.uk Emley Moor (870kW) Winterhill (500kW) Moel-y-Parc (100kW) Sutton Coldfield (1000kW) The Wrekin (100kW) Sascha Schediwy: sws@astro.ox.ac.uk Fermilab: October 2009

  20. Jodrell Bank RFI Sascha Schediwy: sws@astro.ox.ac.uk http://2-pad.physics.ox.ac.uk Sascha Schediwy: sws@astro.ox.ac.uk Fermilab: October 2009

  21. Future Deployment Sascha Schediwy: sws@astro.ox.ac.uk http://2-pad.physics.ox.ac.uk Sascha Schediwy: sws@astro.ox.ac.uk Fermilab: October 2009

  22. Dual Polarisation All Digital Aperture Array

  23. Antenna (ANT) & Balun (BAL) ANT BAL LNA SRC FIL CXA GCM CAT SPL SCM MID TLB CXB CXC Sascha Schediwy – Danny Price 2-pad.physics.ox.ac.uk ORA BECA FlowPAD LPDA Sascha Schediwy: sws@astro.ox.ac.uk

  24. Low Noise Amplifiers (LNA) ANT BAL LNA SRC FIL CXA GCM CAT SPL SCM MID TLB CXB CXC Sascha Schediwy – Danny Price 2-pad.physics.ox.ac.uk Sascha Schediwy: sws@astro.ox.ac.uk

  25. Filter Module (FIL) Sascha Schediwy – Danny Price 2-pad.physics.ox.ac.uk ANT BAL LNA SRC FIL CXA GCM CAT SPL SCM MID TLB CXB CXC Sascha Schediwy: sws@astro.ox.ac.uk

  26. Gain Chain Module (GCM) ANT BAL LNA SRC FIL CXA GCM CAT SPL SCM MID TLB CXB CXC Sascha Schediwy – Danny Price 2-pad.physics.ox.ac.uk Sascha Schediwy: sws@astro.ox.ac.uk

  27. Category-7 Cable (CAT) ANT BAL LNA SRC FIL CXA GCM CAT SPL SCM MID TLB CXB CXC Sascha Schediwy – sws@astro.ox.ac.uk 2-pad.physics.ox.ac.uk Sascha Schediwy: sws@astro.ox.ac.uk

  28. Splitter Balun (SPL) ANT BAL LNA SRC FIL CXA GCM CAT SPL SCM MID TLB CXB CXC Sascha Schediwy – Danny Price 2-pad.physics.ox.ac.uk Sascha Schediwy: sws@astro.ox.ac.uk

  29. Signal Conditioning Module ANT BAL LNA SRC FIL CXA GCM CAT SPL SCM MID TLB CXB CXC Sascha Schediwy – Danny Price 2-pad.physics.ox.ac.uk Sascha Schediwy: sws@astro.ox.ac.uk

  30. Translator Board (TLB) ANT BAL LNA SRC FIL CXA GCM CAT SPL SCM MID TLB CXB CXC Sascha Schediwy – Danny Price 2-pad.physics.ox.ac.uk Sascha Schediwy: sws@astro.ox.ac.uk

  31. Coaxial Cables ANT BAL LNA SRC FIL CXA GCM CAT SPL SCM MID TLB CXB CXC Sascha Schediwy – Danny Price 2-pad.physics.ox.ac.uk CXA SRC CXB CXC Sascha Schediwy: sws@astro.ox.ac.uk

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