The satellite communication (satcom) system consists of two parts, the space segment and the ground segment. Communication satellites and measurement and control stations are collectively referred to as the space segment. A typical ground segment is an earth station.
The earth station is an important part of the satellite communication (satcom) system. It generally consists of antennas, feeder equipment, transmitting equipment, receiving equipment, channel terminal equipment, power supply equipment, automatic tracking equipment, and adjacent equipment.
The parabolic reflector of the parabolic antenna concentrates the radio waves into a narrow beam, which has strong directivity, reduces the loss of radio waves when propagating in space, and ensures that the transponders and earth station equipment on the communication satellite receive normal signals. With automatic tracking equipment in the earth station, the antenna is always aimed at the satellite in the sky.
The earth station is composed of high power amplifier, low noise amplifier, combiner, distributor, up converter, down converter, modulator, demodulator and baseband equipment. Taking telephone communication as an example, the telephone signal is first transmitted from the long-distance telephone office to the earth station through the ground transmission system. The baseband equipment in the earth station processes the signal to make it a baseband signal in line with satellite transmission. Then the baseband signal is sent to the modulator and modulated into an intermediate frequency signal of 70MHz or 140MHz. The intermediate frequency signal is converted into an uplink carrier signal with a carrier frequency of 6MHz by an upconverter. This signal is finally sent to a high-power amplifier to amplify to the required transmission power, and sent to the satellite by the antenna. The above is the processing process of the signal in the transmitting equipment of the earth station. The receiving process is just the opposite.
Very Small Antenna Earth Station (VSAT), slightly different. Its antenna diameter is small, generally only 0.3 ~ 2.4m. With it, users can directly use satellites to communicate without the need for tandem through the ground communication network. VSAT combines high-power amplifier, low-noise amplifier and up-down converter into one component, called low-noise combiner (LNB) or low-noise converter (LNC), which can be installed outdoors and communicated with indoor units with cables. Thereby simplifying the structure.
The antenna system is the entrance and exit for the satellite to send and receive radio signals. According to communication needs, antennas include global beam antennas, regional beam antennas, domestic beam antennas, and spot beam antennas.
The space transponder system is the main body of the satellite, which is used to amplify, convert the frequency and then retransmit the radio signal received by the antenna. There are several to dozens of transponders on a communication satellite, and each transponder can simultaneously receive and transmit signals from multiple earth stations.
The position control and attitude control system is used to maintain and control the correct position and attitude of the satellite in orbit. The telemetry command system is used to inform the ground measurement and control station of the satellite's working conditions in time, and receive the command signal sent by the ground measurement and control station, so that the on-board equipment operates according to the command.
The power system is used to provide the electrical energy required for the work of the equipment on the star, including solar arrays, battery packs, etc. The above devices are all installed in the shell made of high temperature resistant and light metal materials.
TT&C is short for Tracking, Telemetry, Command and Monitoring (TTC & M). The task of the measurement and control station is to accurately and reliably track and measure satellites, and to control satellites such as orbit correction, position maintenance, and attitude maintenance. A measurement and control station can monitor and control multiple satellites, but a satellite can only be monitored and controlled by a specific measurement and control station at the same time.