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Introduction
Antenna is one of the most important elements in communication systems as it is used at both transmitters and receivers. When both transmitter and receiver are stationary simple communication occurs but if any one of the antenna is moving then tracking of that antenna becomes necessary. In case of satellite communication when satellite is moving the transmitter or receiver antennas should rotate to receive the signals of maximum strength. Thus here preciseness is the most important factor. Feeding received signal from an antenna to a system that will compare it to the previous signal and according to it will give instructions to the stepper motor to rotate the antenna to a point of maximum signal strength is the core idea of this project.
An antenna tracking system allows an antenna (e.g. 4 meter dish) to be steered in the direction of a satellite passing overhead. The dynamics are such that this process requires at least two degrees of freedom for a tracking head. Traditionally, tracking heads have adopted the Azimuth/Elevation principle in which the elevation angle is limited to +90 degrees from the horizontal position and the Azimuth axis can cover at least 360 degrees of travel.
The antenna needs to be pointed as precisely as possible towards the satellite in order to maximize the antenna gain in the direction of the satellite and hence the transmitted and/or received Signal strength. In principle, the satellite occupies a fixed position in space and consequently ground-based antennas do not need to be constantly steered to follow the satellite's movements.
Small antennas, such as those used for direct reception of satellite broadcasts in the home, can be pointed manually and are insensitive to the small variations in the satellite's position in space. This is because the beamwidth is relatively large and the gain remains approximately constant as the satellite moves with respect to its nominal orbital position. Large ground-based antennas have a narrow beamwidth and the satellite's movements can take it outside of the beam, causing a significant reduction in the antenna gain and hence the signal strength received at the satellite or on the ground. The solution is to use an automatic tracking system that constantly re-points the antenna towards the satellite. So there exist need for “automatic antenna tracking system”.
Automatic tracking systems are not necessary for the smallest antennas; nevertheless it is very important to point the antenna precisely when it is installed to ensure that it is not susceptible to interference from other satellite systems. For antennas that transmit, precise alignment is even more important because a badly pointed antenna can interfere with other systems and services. The smallest antennas are the most susceptible to interference when mispointed because of their large beamwidth, which can "capture" a significant proportion of unwanted signal power from nearby satellites.
Objective and aim of the Automatic Antenna Tracking System:
The purpose of a tracking system is to determine the location or direction of a target on a near-continuous basis. An ideal tracking system would maintain contact and constantly update the target's bearing (azimuth), range and elevation. The output of the tracking system can be sent to a computer system or to a dedicated microcontroller, which stores the information and derives the target's motion and therefore its future position.
• Highest level of transportability
• Optimum performance
• Maximum reliability
• Complete elevation coverage
• Overhead pass capability
• Lowest cost
• High Accuracy/ Preciseness
• Fully Automated (Unattended, dependable operation)
Applications:
1) In navy systems:
A need exists for an inexpensive lightweight portable Tactical Antenna Switching and Positioning System to be employed on ships. The system should be capable of unattended operation, and continuous tracking of UHF geosynchronous satellites despite ship movement and periodic blockage of the satellite by the ship's superstructure
2) In military:
Automatic antenna tracking system has advanced remarkably and applications are now expanding rapidly, particularly in the use of very small aperture terminals (VSATs). In many instances, military forces are required to establish and maintain communications via SATCOM (using VSATs) while stationed temporarily on Navy ships.
3) Vehicle tracking system:
In many advanced countries vehicles with a GPS antenna pre-installed are available. The antenna continuously tracks the GPS satellite for knowing the exact location of the vehicle and the controller unit displays it on a display. This system is very useful for vehicle driver for finding the exact and shortest path.
4) Weather Satellite image reception:
There is no doubt that meteorological imagery from weather satellite systems using automatic antenna tracking system has greatly enhanced our ability to predict weather conditions around the world. To get information from different weather satellites using single antenna it is very convenient to use an automatic antenna tracking system since if one satellite fails to give information about weather the antenna automatically tracks other satellite. Processed weather satellite images are commonly used by television stations to give viewers a more visual impression of weather conditions. The weather is important to those who travel and those who supply services that can be affected by the weather.
Terminologies used:
Adjacent Channel Interference:
Unwanted electrical interference from signals that are immediately adjacent in frequency to the desired signal. This can arise due to imperfections in the transmission channel and/or equipment.
Azimuth:
The pointing direction of an antenna measured in the local horizontal plane in a clockwise direction from north. It is the horizontal co-ordinate that is used to align a satellite antenna. See also Elevation.
Beamwidth:
Measure of the ability of an antenna to focus signal energy towards a particular direction in space (e.g. towards the satellite for a ground-based transmitting antenna), or to collect signal energy from a particular direction in space (e.g. from the satellite for a ground-based receiving antenna). The beamwidth is measured in a plane containing the direction of maximum signal strength. It is usually expressed as the angular separation between the two directions in which the signal strength is reduced to one-half of the maximum value (the -3 db half-power points).
Elevation:
The angle measured in the local vertical plane between the satellite and the local horizon. It is the vertical co-ordinate that is used to align a satellite antenna. See also Azimuth.
Tracking:
The process of continuously adjusting the orientation of an antenna so that its bore sight follows the movements of the satellite about its nominal position. Used in earth stations equipped with large antennas and earth stations operating to satellites in inclined orbit.