Versatile 12m16m Antenna for the SKA

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Versatile 12m/16m Antenna for the SKA S.
Weinreb, sweinreb_at_caltech.edu An antenna for the
0.1 to 34 GHz range is proposed. The antenna will
utilize a solid hydroformed surface for the inner
12m diameter and incorporate a 2m mesh rim
addition to provide 16m diameter for lt 1.5 GHz.
The 12m surface will be shaped to allow high
efficiency for cooled secondary focus receivers
covering 1.2 to 11 GHz and 11 to 34 GHz. A prime
focus receiver is then used for 0.1 to 1.5 GHz. A
36 element 0.7 to 1.4 GHz focal-plane array can
map a 200 square degree field. This receiver
flips around the Gregorian subreflector and can
be used for wide field of view (90 degrees)
surveys. The total collecting area in this
"flipped feed" mode is 3600wavelength squared
for the 4500 element US SKA concept. This is the
equivalent to a 250m paraboloid at 100 MHz.
Decade bandwidth feeds with beamwidths
appropriate for this F/D are also described.
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Versatile 12m/16m Antenna for SKARationale

• We need to consider Frequency of View (FROV) as
  well as Field of View (FOV)
• This antenna, feeds, and receivers cover the
  entire 0.1 to 25 GHz specified for the SKA. No
  other concept can make this statement.
• Instantaneous FROVs are 0.1 to 1.5 GHz, 1.2 to
  11 GHz, and 11 to 34 GHz. Change from one band
  to another can be accomplished in less than 1
  minute.
• The number of required receivers is manageable
  4500 x 2 x 3 for both polarizations and all three
  bands. Other concepts requiring millions of
  receivers lead to great difficulties in cost,
  maintenance, and updating of hardware.
• A 36 element focal plane array for 0.7 to 1.4
  GHz can provide a 200 square degree FOV and fits
  the optics of the antenna.

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SKA 12m/16m Versatile Antenna - Features

• 12m solid diameter with 2m mesh extension to 16m
  diameter
• Mesh is 10x10mm with 0.56mm diameter SS wire.
  Has lt 5 transmission for F lt 1.5 GHz
• Mesh has approximately 0.1 the wind resistance,
  weight, and cost per unit area compared to solid
• 16m is 4? at 75 MHz. Will be efficient low
  frequency antenna at prime focus.
• 16m F/D.375 with 67O edge angle has very low
  ground pickup with wideband feed. Very low noise
  for 0.5 to 1.5 GHz.
• Shaped reflector and subreflector provides high
  A/T for secondary focus operation 1.2 to 34 GHz
• 0.1 to 1.5 GHz feed can flip to provide 60O FOV
  with collecting area equivalent to a 250m dish at
  100 MHz for 4500 elements.
• Focal plane array for 0.7 to 1.4 GHz fits for 36
  elements covering 200 square degrees.

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Shaped Reflector Geometry to Scale
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From IEEE AP/URSI Symposium, Monterey, CA, June
20-26, 2004 More data is shown in digest paper.
rikard.olsson_at_elmagn.chalmers.se
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Progress Report on Wideband Feed Design at
Chalmers Per-Simon Kildal and Rikard Olsson

• Further computer studies to optimize
  configuration including back reflector size
  documented in 5 reports
• First experimental model constructed and is
  under test

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• Chalmers Feed Study Results Applied to 12/16m
  Concept
• Calculated pattern gives 57 prime focus
  efficiency, 3K spillover, and 0.3K mesh leakage
  in 12/16m symmetric antenna from 0.5 to 1.5 GHz
• Gain is 10.5 /- 0.5 dB and reflection
  coefficient better than 6 dB over 112 frequency
  range. Provides 65 efficiency at half-angles of
  42O to 55
• These results are for infinite ground plane APS
  paper results are for 0.65? ground plane.