Satellite antenna systems can perform as uplinks and downlinks. Uplinks are few and downlinks are many. Satellite is a broadcasting of a signal from one location to many locations. It is a common television and radio solution. But we use it for data transmission too. Often it is an means to develop internet signals to remote or hard to reach destinations. But, in industry we commonly use it for SCADA networks to rural locations as well. SCADA means ‘supervisory control and data acquisition”, and is a command and control solution used in the utilities industry for electricity, water, and gas infrastructure control.
Due to the inherent latency of satellite, it is not ideal for some applications. For example, it adds an annoying delay in voice communications. Yet, satellite voice is used when and where other forms of communications are not available, for example in Canada’s Arctic regions.
Downlinks are by far the most popular satellite antennas that you commonly see today. Designing downlinks is relatively easy. You need to consider the environment and the satellite to be captured as a part of the equation. The rest is just maths to determine the performance parameters and the robustness of the link. Downlinks can be small, as ting as just 0.68 metres. But, they can also be rather large as big as 7.3 metres. Receiving satellite signals is driven by the footprint of the signal coverage that the satellite transponders emit. Physical obstructions like terrain, trees and foliage, structures, and more must all be considered.
The most significant issue is structural wind loading. Satellite antennas are effectively similar to the sail on a boat in so much as they capture the winds and due to the curvature of the parabola they create a high / low pressure on either side of the dish. This change in pressure magnifies the wind forces and places three different loads upon the foundations – dead load, lift, and a rotational load. The dead load is the weight of the antenna and its infrastructure in a downward direction. Add ice and snow and the dead load can vary dramatically. The winds will try to fly the antenna off of the foundation and the lift can be many factors greater than the dead loads. The rotational loads or moments are created when the winds try to corkscrew the antenna off of the foundations. The torque can be significant. All wind loads are aggravated by wind shears especially when several large building disrupt the smooth flow of the wind.
Uplinks demand even more precision in the design and greater rigidity of the foundations. The larger the uplink antenna the narrower the beamwidth of the transmit signal that dictates serious stability for the antenna systems and foundations. For example, with a 4.5 metre transmit antenna, the beamwidth is +/- 0.25 of a degree. So, any movements beyond this tolerance impacts the signal from reaching the satellite. A simple movement of +/- 0.25° is a 3 dB loss (50%) of signal to the satellite which is a major loss and will likely result in a service outage.
Polarization of the signals is critical for both downlinks and uplinks. Most satellites use a vertical / horizontal polarization, but some use a circular polarization with left-hand and right-hand rotation of the signal. As a result, it is critical to know the polarization so acquire the right equipment for it all to work.