Scalable 100 GHz focal plane arrays: a 16-pixel wideband array for the Green Bank Telescope

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The development of large format detector arrays for millimeter-wavelength spectroscopy offers great opportunity for new discovery, potentially enabling molecular line surveys that efficiently map the dynamics and distribution of star-forming gas with high angular and spectral resolution over large areas of sky. The challenge to building large spectroscopic arrays is technical rather than fundamental: each pixel in the array must be a complete and independent heterodyne spectrometer. In the astronomically important frequency range of 5-170 GHz (wavelength 1.8-60 mm), amplifiers based on High Electron Mobility Transistors (HEMTs) offer low noise, low power dissipation, high reliability, inherently wide bandwidths, and the ability to build instruments with high spectral resolution. Under a previous NSF award, Dr. S. Church of Stanford Univ. and her collaborators developed the necessary complex fabrication techniques and constructed prototype components for such an instrument using single-pixel feed horns, low-noise Monolithic Millimeter-wave Integrated Circuit (MMIC) amplifiers, and Field Programmable Gate Arrays (FPGAs) as the signal-processing components. The current proposal aims to extend this technology toward mass-production and machine-assembly with the 16-channel Argus spectrometer targeted for W-band (85-116 GHz) observations at the 100m Green Bank Telescope (GBT) of the National Radio Astronomy Observatory. While a 16-pixel detector will not fully exploit the potential of this approach, it is well-matched to the field of view offered by the GBT and its scalable design will provide a proof of both concept and fabrication technique for future arrays with perhaps hundreds of pixels on other telescopes. Though not intended as a GBT facility instrument, Argus will be opened to collaborative research use by the general astronomical community. The project will also foster the training of students and young researchers through direct hands-on involvement in the instrument development as well as ongoing outreach efforts in area community colleges and high schools.Funding for the development of MMIC-based multi-channel mm-wave spectrometers is being provided by NSF's Division of Astronomical Sciences through its Advanced Technologies and Instrumentation program.