US SKA Feeds and Receiver Development Summary Plan – Nov 30, 2007.
US SKA Feeds and Receiver DevelopmentSummary Plan – Nov 30, 2007
Wideband Feeds Under Development at Cornell (Cortes), NRAO (Bradley), Chalmers (Kildal), Berkeley (Welch), and Caltech (Weinreb). A frequency range of 0.5-10 GHz with Tsys < 30K is challenging. Approach is CAD modeling, followed by pattern and reflection tests, and then Tsys and efficiency measurements on a reflector with optics matching the feed.
LNA’s – For 0.5-10 GHz current HEMT LNA’s give < 6K noise if cooled to 15K, or < 20K noise if cooled to 60K which is much preferred for SKA because of operating and capital costs. Development of improved HEMT’s and SiGe LNA’s will have goal of < 8 K noise at 10 GHz and 60K. For < 3 GHz CMOS or SiGe LNA’s operating at 300K may be adequate.
Integration of antenna, feed, LNA, and cooler is crucial as Tsys will be dominated by losses. Cooled feed is required at > 3 GHz but is very difficult at 0.5 GHz; a split cooled/uncooled feed or two feeds, 0.5 – 3 at 300K and 1.2 – 12 GHz at 60K will be investigated.
Affordable manufacture and maintenance in quantities of thousands.
An educational 34m radio telescope, GAVRT, DSS28, will be an “SKA Phase 0” test bed for a 0.5 to 14 GHz system realized with two commercial wideband feeds.
They are manufactured by the ETS-Lindgren company based in Finland.
Model 3164-06, 0.5 to 4 GHz
LNA cooled to 70K
Model 3164-05, 2 to 14 GHz
Feed and LNA cooled to 15K
Measured Noise Temperature of GAVRT Receiver
DSS28 Total Efficiency with 2-14 GHz FeedComputed* using measured phase and amplitude patterns of Lindgren feed Reflector rms of 0.3mm = .012” and 10% strut blockage assumed.Cross-polarization is -15 to -20 dB
* See W. Imbriale, “Design of a Wideband Radio Telescope”, IEEE Aerospace Conference, Big Sky, MT, March, 2007.
Tsys Breakdown Showing Contributions from LNA, Connections, and Feed
This example shows current values for 0.5 to 3 GHz receiver on GAVRT telescope and shows development goals for SKA by 2010.