ata antennas feeds and systems nsf review 8/05/08 jack welch
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ATA Antennas Feeds and Systems
NSF Review 8/05/08
Jack Welch
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The Allen Telescope Array of 350 dishes in Northern CA ~ 2010
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Array of a Large Number of Small Dishes (LNSD)
• A Survey Telescope with large field of View
• For Multiple Pointings, point source sensitivity is proportional to ND, not NDD
• Single Wide Band Feed insures frequency agility
• Complementary to other cm wave telescopes
• US Pathfinder for the SKA mid-band
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A “Green Telescope”
• All ambient antenna heating and cooling is done by underground air flow
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ATA - 350 Dishes Made By
TVRO Companies
2.4m secondary2.4m secondary
6m primary6m primary
Log-periodic FeedLog-periodic Feed with Actuatorwith Actuator
ShroudShroud
Radome
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6m Antenna Optics
• Offset Gregorian - Unblocked Aperture• Higher Gain• Lower sidelobes -15db• Shroud lowers spillover and background
noise and interference• Total surface RMS=.7mm• Wide field of View: 3degrees at 1 GHz• Aperture efficiency > 0.6
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The Antenna Pattern
At 2.3 GHz
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Dewar/Cryo
12”
Dewar
Refrigerator
LNAs
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Wideband Feed (Log Periodic)
• Range: 0.5 – 11 GHz• Input reflection < -15 db• LNA within dewar at 62K• Cryocooler inside the feed• Feed gain 11.5 db +/- 1 db• Feed f/D = .65• All receiver electronics a part of the feed• Entire analog band sent to lab in fibers• Dual linear polarization
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Overall System
• Four RF Downconverters produce 600 MHz Dual Polarized Bands at Any Input Frequency
• Filters feed 100 MHz bands to backends• AD Converters (8 bit) drive Spectral Correlators
and beamformers• Simultaneous SETI and other astronomy
Observing Enabled• Good Overall gain Stability for Single Antenna
Observations of Large Scale Structure
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