Earth Stations Earth stations are the interface point for communications to and from the satellite[Ha, 1986. An earth station can be divided into two subsystems, the transmit chain and the receive chain. A common element between the transmit and receive chain is the antenna. Because of the large signal attenuation at RF frequencies, the earth station antenna must have high signal gain and be highly directional to focus the power to and from the satellite. A parabolic-shaped reflector antenna is used by earth stations since it can provide these characteristics The transmit chain consists of several major components: baseband equipment, modulators, frequency upconverters, high-power amplifiers(HPA), and combiner circuitry used to switch the output of the HPAs to the antenna. The receive chain uses a low-noise amplifier to receive the satellite signals, frequency downcon- verters, demodulator, and baseband equipment. In the transit chain the signals are modulated, combined, and frequency-shifted with an upconverter to the desired satellite transmit frequency. After upconversion, the signals are amplified by HPAs. In a large earth station there may be many HPAs which feed to a single antenna. These signals must be switched and combined appro- priately At microwave frequencies, waveguide combiners are used to route the output of the HPAs to the antenna In the receive chain, the counterpart to the HPA is the low-noise amplifier(LNA), which is used to amplify the signals received from the antenna. This amplifier must be designed for maximum gain with a very small oise contribution. The noise generated in this unit contributes significantly to the overall performance of the receive side of the earth station. Gallium arsenide( gaAs) FETs are commonly used in the amplifier section of the lna because of their low-noise characteristics. The LNA feeds the signal to the frequency downconvert which converts it to IF frequency suitable for demodulator A hub monitoring and control(M&C)system provides the monitoring and control of the RF equipment and baseband equipment. Redundant RF equipment is common at a hub, and the M& C system is used to monitor the components and provide automatic switchover in the event of equipment failure. Switchover between equipment can occur either by operator initiation or automatically by the M&C upon sensing an Technical characteristics of large earth stations have been established for use with the INTELSAT syste S NTELSAT categorizes two types of earth stations: multipurpose and special purpose. A multipurpose carth purpose standard A, B, and C earth stations have antenna diameters from 11 to 33 meters. Special-purpose standard D, E, and F earth stations have antenna diameters between 3.5 to 11 meters In addition to fixed earth stations, "portable"earth stations, called transportables, have been manufactured which can be taken to locations originating the programming. These transportables are usually mounted on a truck or trailer and include all the components necessary for an earth station. In the case of the transportable, the antenna size is selected to be as small as 4 meters in diameter. a transportable earth station is designed to be upgraded with"building blocks"to handle heavy, medium, and thin route traffic Transportable earth stations temporary carrier service, backup during the retrofit of an existing earth station, and disaster recover ons, are designed to meet the requirements for various applications such as temporary business communicat Another type of earth station is the flyaway. This is a small remote satellite terminal which can be packed into suitcases for shipment on an airline for delivery anywhere in the world. These systems consist of a small antenna, RF unit, and baseband equipment to provide a complete satellite communications station. An example is an L-band version which provides audio communications via the Inmarsat system Fitting into a small suitcase, it contains a telephone handset RF electronics, and antenna that can be assembled to provide audio comI ications anywhere in the world. Mobile satellite terminals are even smaller, suitable to be carried as handheld or briefcase units VSAT Communication System Advances in technology have revolutionized the satellite communications industry by deployment of very small aperture terminal (VSAT)networks for data, voice, and video communication. Since the mid-1980s, VSAT networks have become widely used in the oil, lodging, financial, auto, retail, and manufacturing industries By the 1990s, VSATs were operating in C and Ku-bands. Also by the mid-1990s, over 70% of the VSAT market e 2000 by CRC Press LLC© 2000 by CRC Press LLC Earth Stations Earth stations are the interface point for communications to and from the satellite [Ha, 1986]. An earth station can be divided into two subsystems, the transmit chain and the receive chain. A common element between the transmit and receive chain is the antenna. Because of the large signal attenuation at RF frequencies, the earth station antenna must have high signal gain and be highly directional to focus the power to and from the satellite. A parabolic-shaped reflector antenna is used by earth stations since it can provide these characteristics. The transmit chain consists of several major components: baseband equipment, modulators, frequency upconverters, high-power amplifiers (HPA), and combiner circuitry used to switch the output of the HPAs to the antenna. The receive chain uses a low-noise amplifier to receive the satellite signals, frequency downcon￾verters, demodulator, and baseband equipment. In the transit chain the signals are modulated, combined, and frequency-shifted with an upconverter to the desired satellite transmit frequency. After upconversion, the signals are amplified by HPAs. In a large earth station, there may be many HPAs which feed to a single antenna. These signals must be switched and combined appro￾priately. At microwave frequencies, waveguide combiners are used to route the output of the HPAs to the antenna. In the receive chain, the counterpart to the HPA is the low-noise amplifier (LNA), which is used to amplify the signals received from the antenna. This amplifier must be designed for maximum gain with a very small noise contribution. The noise generated in this unit contributes significantly to the overall performance of the receive side of the earth station. Gallium arsenide (GaAs) FETs are commonly used in the amplifier section of the LNA because of their low-noise characteristics. The LNA feeds the signal to the frequency downconverter, which converts it to IF frequency suitable for demodulator. A hub monitoring and control (M&C) system provides the monitoring and control of the RF equipment and baseband equipment. Redundant RF equipment is common at a hub, and the M&C system is used to monitor the components and provide automatic switchover in the event of equipment failure. Switchover between equipment can occur either by operator initiation or automatically by the M&C upon sensing an equipment failure. Technical characteristics of large earth stations have been established for use with the INTELSAT system. INTELSAT categorizes two types of earth stations: multipurpose and special purpose. A multipurpose earth station can be used with any service, while a special-purpose earth station is restricted. Multipurpose standard A, B, and C earth stations have antenna diameters from 11 to 33 meters. Special-purpose standard D, E, and F earth stations have antenna diameters between 3.5 to 11 meters. In addition to fixed earth stations, “portable” earth stations, called transportables, have been manufactured which can be taken to locations originating the programming. These transportables are usually mounted on a truck or trailer and include all the components necessary for an earth station. In the case of the transportable, the antenna size is selected to be as small as 4 meters in diameter. A transportable earth station is designed to be upgraded with “building blocks” to handle heavy, medium, and thin route traffic. Transportable earth stations are designed to meet the requirements for various applications such as temporary business communications, temporary carrier service, backup during the retrofit of an existing earth station, and disaster recovery. Another type of earth station is the flyaway. This is a small remote satellite terminal which can be packed into suitcases for shipment on an airline for delivery anywhere in the world. These systems consist of a small antenna, RF unit, and baseband equipment to provide a complete satellite communications station. An example is an L-band version which provides audio communications via the Inmarsat system. Fitting into a small suitcase, it contains a telephone handset, RF electronics, and antenna that can be assembled to provide audio commu￾nications anywhere in the world. Mobile satellite terminals are even smaller, suitable to be carried as handheld or briefcase units. VSAT Communication System Advances in technology have revolutionized the satellite communications industry by deployment of very small aperture terminal (VSAT) networks for data, voice, and video communication. Since the mid-1980s, VSAT networks have become widely used in the oil, lodging, financial, auto, retail, and manufacturing industries. By the 1990s, VSATs were operating in C and Ku-bands. Also by the mid-1990s, over 70% of the VSAT market