KVN and VERA Array

Aperture Efficiency

The aperture efficiency of each VERA antenna is about 40-50% in both K band and Q band (table 4 for the 2012 data). These values will be measured and updated in 2014-2015 winter season.

These measurements were based on the observations of Jupiter assuming that the brightness temperature of Jupiter is 160 K in both the K band and the Q band. Due to the bad weather condition in some of the sessions, the measured efficiencies show large scatter. However, we conclude that the aperture efficiencies are not significantly changed compared with previous measurements. The elevation dependence of aperture efficiency for VERA antenna was also measured from the observation toward maser sources.

Table 4:Aperture efficiency and beam size of KaVA antennas.
K band (22 GHz) Q band (43 GHz)
HPBW HPBW
Antenna Name (%) (arcsec) (%) (arcsec)
Mizusawa 44 146 51 76
Iriki 47 142 41 73
Ogasawara 48 143 46 74
Ishigakijima 41 138 42 75
Yonsei 55 119 60 62
Ulsan 60 120 56 62
Tamna 59 123 62 62

Figures 3 shows the relations between the elevation and the aperture efficiency measured for VERA Iriki station. The gain curves are measured by observing the total power spectra of intense maser sources. The aperture efficiency in low elevation of  deg decreases slightly, but this decrease is less than about 10%. Concerning this elevation dependence, the observing data FITS file include a gain curve table (GC table), which is AIPS readable, in order to calibrate the dependence when the data reduction.

The aperture efficiency and beam size for each KVN antenna are also listed in Table 4. Aperture efficiency of KVN varies with elevation as shown in Figure 3. The main reflector panels of KVN antennas were installed to give the maximum gain at the elevation angle of 48. The sagging of sub-reflector 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 antennas use a hexapod to adjust sub-reflector position. Figure 3 shows the elevation dependence of antenna aperture efficiency of the KVN 21 m radio telescopes measured by observing Venus or Jupiter. 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:

(1)

where EL is the elevation in degree.
figure 3:the elevation dependence of the aperture efficiency for kvn three antennas and vera iriki antenna. for kvn antennas, the maximum gain is given at the elevation angle of 48. The efficiency in K-band (on Feb 8, 2005) and the Q-band (on Feb 12, 2005) for VERA Iriki antenna is shown in bottom right. The efficiency is relative value to the measurement at EL = 50 .

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KaVA ( KVN and VERA Array )