KVN and VERA Array (KaVA)

Beam Pattern and Size

Figure 4 show the beam patterns in the K band. The side-lobe level is less than about -15dB, except for the relatively high side-lobe level of about -10dB for the separation angle of 2.0 deg at Ogasawara station. The side-lobe of the beam patterns has an asymmetric shape, but the main beam has a symmetric Gaussian shape without dependence on separation angle. The measured beam sizes (HPBW) in the K band and the Q band based on the data of the pointing calibration are also summarized in Table 4. The main beam sizes show no dependence on the dual-beam separation angle.

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$^{\circ}$. 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$^{\circ}$.

The optics of KVN antenna is a shaped Cassegrain type of which the main reflector and subreflector are shaped to have a uniform illumination pattern on an aperture plane. Because of the uniform illumination, KVN antennas can get higher aperture efficiency than value of typical Cassegrain type antenna. However, higher side-lobe level is inevitable. OTF images of Jupiter at K and Q bands are shown in Figure 4. The map size is 12' X 10' and the first side-lobe pattern is clearly visible. Typical side-lobe levels of KVN antennas are 13-14dB.

Figure 4: The beam patterns in the K-band for VERA (A-beam) Iriki with the separation angle of 0$^{\circ}$ (Upper left) and Ogasawara with the separation angle of 2.0$^{\circ}$(Upper right), and in K/Q-band for KVN Yonsei. The patterns of VERA antennas were derived from the mapping observation of strong H$_2$O maser toward W49N, which can be assumed as a point source, with grid spacing of $75^{\prime\prime}$. In the case of KVN antennas, the patterns were derived from the OTF images of Venus at K/Q-band.

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KaVA ( KVN and VERA Array )