Antennas for MeerKAT

13-14 March 2008

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) 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 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 TDP AWG, 13-14/3/08, San Francisco

MeerKAT & KAT-7 Site

• Carnavon, Northern Cape, South Africa TDP AWG, 13-14/3/08, San Francisco

MeerKAT & KAT-7 Site

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 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 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 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?

TDP AWG, 13-14/3/08, San Francisco

KAT-7:

Surface Tolerance

Ruze phase error efficiency 1 0.9

0.8

0.7

0.6

0.5

0.4

0.3

0.2

0.1

0 0 1mm RMS error 2mm RMS error 4mm RMS error 2.5

5 7.5

Frequency (GHz) 10 TDP AWG, 13-14/3/08, San Francisco 12.5

15

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 TDP AWG, 13-14/3/08, San Francisco

KAT-7:

Status

• F/D Study – Look at different system temperatures – Optimise A e – F/D = 0.38

/ T sys Directive Pattern 4.5

4 3.5

T sys  = 15K T sys  = 20K T sys  = 25K T sys  = 30K 3 2.5

2 1.5

0.3

TDP AWG, 13-14/3/08, San Francisco 0.32

0.34

0.36

0.38

0.4

F/D 0.42

0.44

0.46

0.48

0.5

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 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) TDP AWG, 13-14/3/08, San Francisco

KAT-7:

Status

TDP AWG, 13-14/3/08, San Francisco

KAT-7:

Status

• Other engineering work for 2008… – OMT development – Cryo-cooling • He versus LN 2 • Development choice – Cryostat development – Cool-box development – Calibration Signal Injection – LNA choice TDP AWG, 13-14/3/08, San Francisco

TDP AWG, 13-14/3/08, San Francisco