The VSAT antenna is required for the reception and transmission of signals to and from the satellite. The appropriate size of the antenna diameter is determined by your SkyVision Account Manager, taking your needs into account. The shape of the coverage pattern of a satellite varies from one satellite to another. As a result, certain geographical locations will require larger antennas for optimal performance. A larger antenna will also result in a higher gain and a narrower transmission beam, which will provide improved rejection of the "side lobes" of adjacent satellites and protection from terrestrial interference.
(Please note that the antenna usually has an elevation offset which you can find in your antenna
You can also view the explanation of the antenna below in the VSAT Installation Manual Components Chapter: