ATA Antennas Feeds and Systems

NSF Review 8/05/08

Jack Welch

The Allen Telescope Array of 350 dishes in Northern CA ~ 2010

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

A “Green Telescope”

• All ambient antenna heating and cooling is done by underground air flow

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

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

The Antenna Pattern

At 2.3 GHz

Dewar/Cryo

12”

Dewar

Refrigerator

LNAs

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

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