I. Antesky Antenna tracking system components and working principle
1. Antenna tracking system composition
Antenna automatic tracking system is mainly composed of indoor antenna control unit (ACU) and outdoor antenna drive unit (ADU).The control command are operated through the programmable terminal display to realized the antenna azimuth, elevation and polarization angle adjustment.
(1) Antenna Control Unit. ACU is the core of the entire ante-sky tracking and control system, the main components are front panel, Computer Motherboard, interface board, Graphics card, IDE control panel, hard drives,Floppy drive, power supply,etc.
(2) Antenna Drive Unit.ADU is installed on the antenna mount, which supplies the necessary electronic and mechanical interface. ADU is mainly composed of antenna control unit, power supply, Overload Relays, Inverter, Indicator,etc.
Bsides the antenna control unit and drive unit, tracking system also include the beacon receiver, azimuth position sensor, elevation position sersor, emergencing switch, polarizaiton position feedback, AC drive motors,etc.
2. Working principle of Antenna tracking system
Beacon signal is transmitted by satellite company, its frequency is fixed with high stability.Different satellite different beacon frequency, after the earth station acquire the necessary beacon signal, the automatic tracking system can make the antenna track the satellite under no intervention. The satellite signal will be passed the feed, Low-noise amplifier (LNA) and sent to the splitter 1:4, then the splitter output will sent it to analyzer spectrum, splitter and beacon receiver. Beacon receiver converts the selected beacon signal to a DC signal with signal strength which is proportional, one way is sent to automatic power control (APC), another way is sent to antenna control unit and is considered as position command reference signal when doing the automatic tracking satellite. In ACU comparing the signals from the position command and position sensor and get the position error signal, this error is compensated by the frequency and is compared with the threshold value; If the error exeed the threshold value, the motor under ADU control will make the antenna move towards the direction which can reduce the error, and make the receiving beacon signals become much more stronger, and the antenna pointing will become more and more correct, when the center of the main beam point to the Satellite, the receiving beacon signal will become the strongest; once the error is lower than the threshold value, ADU will control the motor to keep the antenna postion, the antenna can track the satellite autuomatically under no intervention.
II Control Method of Antenna Tracking System
1.Independent manual control mode
If maintenance will make the antenna angle change a lot, and lead to the antenna deviate the aim far away, the automatic tracking system will stop tracking because of the weak signal, firstly user should use the manual control to make the antenna reset. When adjusting please note the changes of the beacon level, exit the manual control mode when aligning the aim, and get into the mode of step track and op track.
2. Tracking under program control
Program tracking: Compile the predict Satellite orbits and ante-sky antenna pointing angel as the program, and adjust the antenna pointing by the computer.Acturally due to the uneven earth density and other interference effects, it is difficult to canculate the accuracy tracking for a long time.
According to the above working principle, the earth station tracking receiver. get the satellite beacon signal, if the antenna deviate the satellite direction, the tracking receiver will generate an error signal which is proportional to the deviation angel (Az and El). The error signal will guide and control the antenna drive mechanism and adjust the antenna poiting. The advantages of this automatic tracking method is that it can track the satellite continously and the accuracy is much higher.