RF, Microware and Optical Frequency Communications – A Review of Technologies
8. Classification of Satellites
There are different types of communication satellites based on their orbit and their use. Here are some common types:
1. By orbit:
Geostationary satellites: These satellites are placed in a geostationary orbit, which is an orbit at an altitude of approximately 36,000 km above the Earth's equator. They have an orbital period of 24 hours, which allows them to stay fixed in the same position relative to the Earth's surface. Geostationary satellites are commonly used for broadcasting, internet connectivity, and other communication services.
Low Earth Orbit (LEO) satellites: These satellites orbit the Earth at altitudes between 160 and 2,000 km. They have shorter orbital periods than geostationary satellites, typically ranging from 90 minutes to a few hours. LEO satellites are commonly used for communication and remote sensing applications, including mobile satellite communication and Earth observation.
Medium Earth Orbit (MEO) satellites: These satellites orbit the Earth at altitudes between 2,000 and 36,000 km. They have longer orbital periods than LEO satellites, typically ranging from 2 to 24 hours. MEO satellites are commonly used for navigation and positioning applications, including the Global Positioning System (GPS).
2. By use:
Fixed communication satellites: These satellites provide a fixed connection between two points on the Earth's surface. They are commonly used for satellite phone communication, direct-to-home (DTH) television broadcasting, and other fixed communication services.
Mobile communication satellites: These satellites provide communication services for moving vehicles, including airplanes, ships, and land vehicles. They are commonly used for mobile satellite phone communication, in-flight connectivity, and maritime communication.
Earth observation satellites: These satellites are used for remote sensing and imaging of the Earth's surface. They provide high-resolution images for various applications, including environmental monitoring, disaster management, and agriculture.
Navigation satellites: These satellites are used for positioning, navigation, and timing applications. They include the GPS, GLONASS, and Galileo satellite systems, which provide location information for various applications, including navigation, transportation, and surveying.
Note: Difference between geostationary and geosynchronous orbits?
Geostationary and geosynchronous orbits are similar in that they both refer to orbits around the Earth at an altitude of approximately 36,000 km. However, there is an important difference between the two.
A geostationary orbit is a specific type of geosynchronous orbit where a satellite's orbital period is exactly 24 hours, matching the Earth's rotational period. This means that the satellite appears to remain fixed in the sky above a particular point on the Earth's surface. This is useful for communication satellites, which can provide continuous coverage of a specific geographic region.
In contrast, a geosynchronous orbit is any orbit that has an orbital period that matches the Earth's rotational period, regardless of the inclination or position of the orbit. This means that a geosynchronous satellite may move north and south in the sky, rather than appearing fixed in one position like a geostationary satellite.
In other words, all geostationary orbits are geosynchronous, but not all geosynchronous orbits are geostationary.
9. Satellite transponder frequencies and uses
Transponders on satellites are used to receive signals from Earth stations, amplify the signals, and retransmit them back to the ground. The bandwidth available on each satellite frequency band, as well as their typical applications, are as follows:
1. L-band (1 GHz to 2 GHz): The L-band is primarily used for mobile satellite services, such as satellite phones, satellite radio, and GPS. It is also used for some military communications and remote sensing applications.
2. S-band (2 GHz to 4 GHz): The S-band is used for a variety of communication applications, including satellite-based navigation and weather monitoring. It is also used for some mobile satellite services and some military communications.
3. C-band (4 GHz to 8 GHz): The C-band is one of the most widely used frequency bands for satellite communications, particularly for commercial applications such as broadcasting and telecommunications. It is also used for some military and government communications, as well as for weather monitoring and remote sensing.
4. X-band (8 GHz to 12 GHz): The X-band is used for a variety of communication and sensing applications, particularly for military and government communications. It is also used for some commercial applications, such as satellite-based radar and remote sensing.
5. Ku-band (12 GHz to 18 GHz): The Ku-band is widely used for direct broadcast satellite (DBS) services, including satellite TV and satellite-based internet. It is also used for some military and government communications, as well as for remote sensing and weather monitoring.
6. Ka-band (26.5 GHz to 40 GHz): The Ka-band is used for high-speed satellite communications, particularly for broadband internet and other data-intensive applications. It is also used for some remote sensing and weather monitoring applications.
It's important to note that the bandwidth available on each frequency band can vary depending on the particular satellite and transponder used. Additionally, some frequency bands may be allocated for specific uses or restricted in certain geographic regions.
