antennas for meerkat 13-14 march 2008. tdp awg, 13-14/3/08, san francisco meerkat semantics k.a.t. =...
TRANSCRIPT
Antennas for MeerKAT
13-14 March 2008
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)
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 106)– 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
0 2.5 5 7.5 10 12.5 150
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
Frequency (GHz)
Eff
icie
ncy
Ruze phase error efficiency
1mm RMS error
2mm RMS error4mm RMS error
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 possiblebeam widths
TDP AWG, 13-14/3/08, San Francisco
KAT-7: Status
• F/D Study– Look at different system temperatures
– Optimise Ae / Tsys
– F/D = 0.38
0.3 0.32 0.34 0.36 0.38 0.4 0.42 0.44 0.46 0.48 0.51.5
2
2.5
3
3.5
4
4.5
F/D
Ae /
Tsy
s [
m2 /K
]
Directive Pattern
Tsys
= 15K
Tsys
= 20K
Tsys
= 25K
Tsys
= 30K
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
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 LN2 choice
• Development
– Cryostat development– Cool-box development– Calibration Signal Injection– LNA choice
TDP AWG, 13-14/3/08, San Francisco