Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Tilted Beam Measurement of VLBI Receiver for the South Pole Telescope   We have developed a 230 and 345 GHz very-long-baseline interferometry (VLBI)
receiver for the South Pole Telescope (SPT). With the receiver installed, the
SPT has joined the global Event Horizon Telescope (EHT) array. The receiver
optics select the 230 or 345 GHz mixers by rotating the tertiary mirror around
the optical axis, directing the chief ray from the secondary mirror to the feed
horn of the selected frequency band. The tertiary is installed on top of the
receiver cryostat, which contains both mixer assemblies. The feed horns are
placed symmetrically across the centerline of the telescope optics and tilted
inward by 5.7 degrees from the vertical plane so that their beams intersect at
the chief ray intersection on the tertiary mirror. We have performed vector
beam measurements of the SPT VLBI receiver in both frequency bands. The
measurements preserved the relative location of the beams, to establish the
relative locations of the phase centers of the two horns. Measurements in two
parallel reference planes above the cryostat were used to suppress reflected
light. To model the beam, we derive a general expression of the electric field
vector on the measurement plane for a tilted beam and infer the feed horn
position parameters for both frequency bands by fitting models to data with a
Markov chain Monte Carlo (MCMC) method. The inferred parameters such as the
tilt angle of the feed horn are in good agreement with the design. We present
the measurement setup, amplitude and phase pattern of the beam, and the fitting
result here.

28
The categories of this paper are: alg-geom
7
The categories of this paper are: hep-th
0
The categories of this paper are: hep-ph
30
The categories of this paper are: q-alg
35
The categories of this paper are: mtrl-th
15
The categories of this paper are: nucl-ex
21
The categories of this paper are: adap-org
4
The categories of this paper are: cond-mat
31
The categories of this paper are: ao-sci
23
The categories of this paper are: solv-int
11
The categories of this paper are: hep-lat
20
The categories of this paper are: acc-phys
10
The categories of this paper are: q-bio
33
The categories of this paper are: plasm-ph
3
The categories of this paper are: physics
13
The categories of this paper are: quant-ph