Antennas for MeerKAT 13-14 March 2008. TDP AWG, 13-14/3/08, San Francisco MeerKAT Semantics K.A.T. =...

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Transcript of Antennas for MeerKAT 13-14 March 2008. TDP AWG, 13-14/3/08, San Francisco MeerKAT Semantics K.A.T. =...

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Antennas for MeerKAT 13-14 March 2008 Slide 2 TDP AWG, 13-14/3/08, San Francisco MeerKAT Semantics K.A.T. = Karoo Array Telescope KAT is Afrikaans for cat MeerKAT: Afrikaans for more cats, also a small furry animal (from the mongoose family) Slide 3 TDP AWG, 13-14/3/08, San Francisco MeerKAT Antenna Team Antenna Pedestal & reflector Subcontracted to industry Managed by Willem Esterhuyse Feeds Subcontracted to industry (EMSS Antennas) Managed by LJ du Toit Close interaction with RF & Reflector RF Subcontracted to industry Managed by Venkat Lakshmanan Slide 4 TDP AWG, 13-14/3/08, San Francisco MeerKAT Intention South African funds (~ $100 x 10 6 ) Funded by Dept. of Science & Technology Administered by National Research Foundation To be built irrespective of SKA site allocation Must be respectable instrument, not just good Must be of relevance to SKA N ~ 80 D ~ 12m Full instrument first light Q4, 2012 Slide 5 TDP AWG, 13-14/3/08, San Francisco MeerKAT & KAT-7 Site Carnavon, Northern Cape, South Africa Slide 6 TDP AWG, 13-14/3/08, San Francisco MeerKAT & KAT-7 Site Slide 7 TDP AWG, 13-14/3/08, San Francisco MeerKAT Phased Implementation XDM: Q4, 2005 to Q4, 2007 Almost a done deal KAT-7: Q1, 2008 to Q4, 2009 This year and next MeerKAT: Q1, 2008 to Q4, 2012 This year, up to 2012 Slide 8 TDP AWG, 13-14/3/08, San Francisco XDM: Q4, 2005 to Q4, 2007 Single dish prototype at Hartebeesthoek, outside Pretoria Composite surface, concrete pedestal, metal support structure Antenna structure & surface R&D, manufacturing by IST Dynamics Diameter 15m, F = 7.5m (F/D = 0.5) El over Az, feed rotator (1.5m diameter disk) Prime-focus fed (four large metal struts) Frequency band: 1414 to 1670 MHz Stepped-horn & stepped-ridge OMT (EMSS), un-cooled Feed cluster: Seven non-overlapping beams (two populated) Two linear polarizations, analogue RF over fiber (COTS) Thermally stabilized COTS LNAs Prototyping test-bed, not a science instrument Used to set up synergy amongst engineering team System Engineering busy evaluating performance Slide 9 TDP AWG, 13-14/3/08, San Francisco KAT-7: Q1, 2008 to Q4, 2009 Seven antenna interferometer, on proposed SKA site First-light scheduled to be Q3, 2009 Limited science instrument, and interferometer test-bed Although small, must be respectable instrument, prototyping errors to be avoided first time around Composite surface, concrete pedestal, metal support structure Antenna structure & surface: Tenders to go out within weeks Diameter 12m, F = 4.56m (F/D = 0.38, optimized for horn & WBF at prime focus El over Az, single-pixel feed, no field rotator Frequency band: 1200 to 2000 MHz (dish tolerances allow >2GHz) Wide flare-angle corrugated horn (four metal struts) Cryogenically cooled OMT & Receiver (probably Sterling) Two linear polarizations, analogue RF over fiber (COTS) Will allow evaluation of remote instrument logistics Slide 10 TDP AWG, 13-14/3/08, San Francisco MeerKAT: Q1, 2008 to Q4, 2012 N ~ 80 interferometer on proposed SKA site Probable topology: Similar to KAT-7 Unless dynamic range requirements dictate otherwise Unless wide-band feed require different F/D Unless upper frequency too high Dynamic Range Considerations N > 80 to be considered Main beam stability, sidelobe and polarization requirements? Offset? Offset and folded? Feed rotator required? Tightened mechanical tolerances? Slide 11 TDP AWG, 13-14/3/08, San Francisco KAT-7: Surface Tolerance Slide 12 TDP AWG, 13-14/3/08, San Francisco KAT-7: Status F/D Study Time scales (dish construction ahead) Accommodate MeerKAT (XDM was for FPAs) No finished feed available Ying wide flare horn Parallel dipoles (radiating as log-periodic antennas) Determine range of possible beam widths Slide 13 TDP AWG, 13-14/3/08, San Francisco KAT-7: Status F/D Study Look at different system temperatures Optimise A e / T sys F/D = 0.38 Slide 14 TDP AWG, 13-14/3/08, San Francisco KAT-7: Status Horn Classic corrugated horn Wide flare (prime focus) Size sub-reflector J(x)/x distribution Optimised on-dish Gain Spill over Still varying radius Slide 15 TDP AWG, 13-14/3/08, San Francisco KAT-7: Status Horn Pattern almost 1 to 2 GHz Match 1.2 to 2 GHz (without OMT) Slide 16 TDP AWG, 13-14/3/08, San Francisco KAT-7: Status Slide 17 TDP AWG, 13-14/3/08, San Francisco KAT-7: Status Other engineering work for 2008 OMT development Cryo-cooling He versus LN 2 choice Development Cryostat development Cool-box development Calibration Signal Injection LNA choice Slide 18 TDP AWG, 13-14/3/08, San Francisco