Korean VLBI Network (KVN)

Gain Curve

The main reflector panels of KVN antennas were installed to give the maximum gain at the elevation angle of 48deg. The sagging of subreflector and the deformation of main reflector by gravity with elevation results in degradation of antenna aperture efficiency with elevation. In order to compensate this effect, KVN antenna use a hexapod to adjust subreflector position. Although this hexapod correction reduces significantly the dependence of aperture efficiency with elevation, the degradation still appears evidently at higher frequency. Following figures show the elevation dependence of antenna aperture efficiency of the KVN 21-m radio telescopes measured by observing Venus or Jupiter using Cross Scan observations.

- Yonsei

YS_Jupiter_2015-03-08_NormalGain
YS_Venus_2015-03-08_NormalGain

- Ulsan

US_Jupiter_2015-04-11_NormalGain
US_RCAS_2016-02-20_GC_lr

- Tamna

TN_Jupiter_2015-04-11_NormalGain
TN_Venus_2015-03-08_NormalGain

By fitting a second order polynomial to the data and normalizing the fitted function with its maximum, we derived a normalized gain curve which has the following form: G_norm = A0*EL^2 + A1*EL + A2, where EL is the elevation in degree. The fitted parameters are summarized in following table.

The fitted parameters are summarized
Yonsei Ulsan Tamna
A0 A1 A2 A0 A1 A2 A0 A1 A2
22L 1.23e-07 6.93e-06 9.99e-01 2.17e-06 -2.63e-04 1.00e+00 -2.40e-06 2.81e-04 9.92e-01
22R -1.32e-06 6.72e-05 9.99e-01 6.17e-06 -6.78e-04 1.01e+00 -2.94e-06 3.52e-04 9.89e-01
43L -2.56e-05 2.47e-03 9.41e-01 2.03e-06 -7.05e-04 1.01e+00 -7.52e-06 7.30e-034 9.82e-01
43R -2.08e-05 1.99e-03 9.52e-01 2.86e-06 -7.72e-04 1.01e+00 -1.13e-05 1.22e-03 9.67e-01
86L -5.15e-05 5.79e-03 8.37e-01 -8.63e-05 8.50e-03 7.90e-01 -1.69e-04 1.58e-02 6.29e-01
86R -4.98e-05 5.60e-03 8.43e-01 -8.63e-05 8.50e-03 7.90e-01 -1.80e-04 1.69e-02 6.03e-01
129L -1.18e-04 1.45e-02 5.34e-01 -1.57e-04 1.43e-02 6.73e-01 -3.24e-04 3.13e-02 2.45e-01
129R -1.11e-04 1.45e-02 5.26e-01 -1.57e-04 1.43e-02 6.73e-01 --- --- ---


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Korean VLBI Network (KVN)