What is a Very Small Aperture Terminal?

M. Rosario

A very small aperture terminal (VSAT) is used to receive and transmit information such as narrowband data, radio frequency identification (RFID) data, and Supervisory Control and Data Acquisition (SCADA). Its name originated from the relatively small dish antenna with a diameter no longer than 10 feet (3 meters). The VSAT is commonly employed for commercial purposes such as transmitting credit card data and giving companies a stable communications infrastructure.

Data from VSATs are usually transmitted from network hubs to satellites that follow a regular orbit.
Data from VSATs are usually transmitted from network hubs to satellites that follow a regular orbit.

Data is usually transmitted from network hubs to satellites that follow a regular orbit. As the satellites get near a satellite ground station, they transmit data to earth. The data transmitted normally varies from 56 Kbit/s to 4 Mbit/s. It is then received by the VSAT using a transceiver which interprets the data for the end user.

The very small aperture terminal functions as a miniature communications antenna that is capable of interacting with other VSATs. It can also act as a two-way satellite ground station, and relay information back to orbiting satellites. This enables real-time communication between the end user and the hub.

Remote locations, such as off shore oil rigs or those that cannot be reached by telephone lines, frequently use a very small aperture terminal to gain access to external communications. Maritime communications, such as those VSAT installed in ships, are typically more complicated. Since the ship is not stationary, the terminal needs to constantly adjust its configuration to align with the satellite.

An average VSAT measures 34 inches (75 centimeters) to 3.93 feet (1.2 meters), making it reasonably portable. Set up of a very small aperture terminal is fairly simple, taking only a few minutes from assembly to operation. Cost of a single terminal is much cheaper compared to traditional satellite antennas. This makes it ideal for locations where building a large satellite antenna would be difficult.

A VSAT transmits data using a private layer-2 network, making security one of its advantages. Broadband data can be transmitted through protocol accelerators on the antenna. Signal strength and dish size still affect the quality of transmission, however.

The topological layout of a very small aperture terminal configuration system is generally classified into three types. A star topology uses a satellite to send data to the terminal. Mesh topology uses a system of strategically spaced terminals to deliver data from the hub to the end user. Combination topology, on the other hand, takes advantage of both star and mesh layouts by having a satellite transmit data to a VSAT mesh, effectively increasing the network's area of coverage.

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