Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: A Highly-Sensitive Cryogenic Phased Array Feed for the Green Bank
  Telescope   In this paper, we describe the development of a new L-band (1.4 GHz)
Cryogenic Phased Array Feed (PAF) system, referred to as the GBT2 array.
Results from initial measurements made with the GBT2 array are also presented.
The PAF was developed for the Green Bank Telescope (GBT) as part of the Focal
L-band Array for the GBT (FLAG) project. During the first stage of the
development work (Phase I), a prototype cryogenic 19 element dual-polarized
array with "Kite" dipole elements was developed and tested on the GBT. The
measured system temperature over efficiency ($T_{sys}/\eta$) ratio for the bore
sight beam of the Kite array was 45.5 K at 1.55 GHz. The off-boresight
$T_{sys}/\eta$ shows an increase by 13 K at an offset equal to the half power
beam width (7$^{'}$.2 at 1.7 GHz). Our measurements indicate that the
off-boresight degradation and field-of-view (FoV) limitation of the Kite array
is simply due to the fixed array size. To increase the FoV, a new 19-element
GBT2 array with larger array spacing was developed during FLAG Phase II. The
frequency response of the array was optimized from 1.2 to 1.6 GHz. A system
with larger cryostat, new low noise amplifiers (LNAs), down-conversion and
digitization close to the front end, unformatted digital transmission over
fiber, ROACH II based polyphase filter banks (PFBs) with bandwidth 150 MHz and
a data acquisition system that records voltage samples from one of the PFB
channels were all developed. The data presented here is processed off-line. The
receiver temperature measured with the new system is 17 K at 1.4 GHz, an
improvement $>$ 8 K over the previous Kite array. Measurements with the GBT2
array on the telescope are in progress. A real time 150 MHz beamformer is also
being developed as part of an NSF-funded collaboration between NRAO/GBO/BYU \&
West Virginia University (Beamformer Project) to support science observations.

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The categories of this paper are: supr-con
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The categories of this paper are: nucl-th
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The categories of this paper are: patt-sol
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The categories of this paper are: nucl-ex
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The categories of this paper are: ao-sci
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The categories of this paper are: cs
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The categories of this paper are: q-fin
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The categories of this paper are: hep-th
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The categories of this paper are: econ
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The categories of this paper are: physics
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The categories of this paper are: math-ph
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The categories of this paper are: gr-qc
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The categories of this paper are: chem-ph
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The categories of this paper are: stat
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The categories of this paper are: eess
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The categories of this paper are: solv-int