"FLAG" - Focal-plane, L-band, Array for the GBT

This web page is the primary system definition and test results resource for a project to build a 1.4-GHz, cryogenic, phased array feed for the GBT. Considerable infrastructure needs to be added to the GBT to accommodate the relatively large number of receiver channels, and the data rates are potentially quite large so the system definition will include everything from the array elements to data archiving and system control. The system design is a work in progress.

Development work for this project has been a collaboration between Brigham Young University and NRAO, and this work continues as the definition of an array for the GBT takes shape. The most recent full array prototype is an ambient temperature, 19-element, single-polarization dipole array that was installed and tested on the Green Bank 20-meter telescope in the summer of 2008 as shown in the photographs. The culmination of these tests was a wide-field map of the Cygnus continuum emission complex, which is shown in the color image below the array photo. A grey-scale composite of the same region assembled from the Canadian Galactic Plane Survey digital continuum images is shown for comparison.

Prototype work is currently underway on a new array receiver with wider channel bandwidth (5 MHz vs 0.5 MHz), dual-polarization dipoles, a Dewar to cool the LNAs, and an FPGA beamformer. All tests to date have streamed raw samples directly to disk and formed beams in post-processing. Bottom-right is a picture of the latest single-polarization array that is designed for wider bandwidth and better noise match with mutual coupling taken into account.








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