File Name: microwave and satellite communication .zip
- Microwave transmission
- An Introduction to Microwave and Satellite Communication
- An Introduction to Microwave and Satellite Communication
A satellite is basically a self-contained communications system with the ability to receive signals from Earth and to retransmit those signals back with the use of a transponder —an integrated receiver and transmitter of radio signals. A satellite has to withstand the shock of being accelerated during launch up to the orbital velocity of 28, km 17, miles an hour and a hostile space environment where it can be subject to radiation and extreme temperatures for its projected operational life, which can last up to 20 years. In addition, satellites have to be light, as the cost of launching a satellite is quite expensive and based on weight. To meet these challenges, satellites must be small and made of lightweight and durable materials.
Microwave transmission is the transmission of information by microwave radio waves. In the s, large transcontinental microwave relay networks, consisting of chains of repeater stations linked by line-of-sight beams of microwaves were built in Europe and America to relay long distance telephone traffic and television programs between cities.
Communication satellites which transferred data between ground stations by microwaves took over much long distance traffic in the s. In recent years, there has been an explosive increase in use of the microwave spectrum by new telecommunication technologies such as wireless networks , and direct-broadcast satellites which broadcast television and radio directly into consumers' homes.
Microwaves are widely used for point-to-point communications because their small wavelength allows conveniently-sized antennas to direct them in narrow beams, which can be pointed directly at the receiving antenna.
This allows nearby microwave equipment to use the same frequencies without interfering with each other, as lower frequency radio waves do. This frequency reuse conserves scarce radio spectrum bandwidth.
Another advantage is that the high frequency of microwaves gives the microwave band a very large information-carrying capacity; the microwave band has a bandwidth 30 times that of all the rest of the radio spectrum below it. A disadvantage is that microwaves are limited to line of sight propagation; they cannot pass around hills or mountains as lower frequency radio waves can.
Microwave radio transmission is commonly used in point-to-point communication systems on the surface of the Earth, in satellite communications , and in deep space radio communications.
Other parts of the microwave radio band are used for radars , radio navigation systems, sensor systems, and radio astronomy. Radio waves in this band are strongly attenuated by the gases of the atmosphere. This limits their practical transmission distance to a few kilometers, so these frequencies cannot be used for long distance communication. The electronic technologies needed in the millimeter wave band are also in an earlier state of development than those of the microwave band.
More recently, microwaves have been used for wireless power transmission. Microwave radio relay is a technology widely used in the s and s for transmitting information, such as long-distance telephone calls and television programs between two terrestrial points on a narrow beam of microwaves. In microwave radio relay, a microwave transmitter and directional antenna transmits a narrow beam of microwaves carrying many channels of information on a line of sight path to another relay station where it is received by a directional antenna and receiver, forming a fixed radio connection between the two points.
The link was often bidirectional, using a transmitter and receiver at each end to transmit data in both directions. For longer distances, the receiving station could function as a relay, retransmitting the received information to another station along its journey. Chains of microwave relay stations were used to transmit telecommunication signals over transcontinental distances. Microwave relay stations were often located on tall buildings and mountaintops, with their antennas on towers to get maximum range.
The launch of communication satellites in the s provided a cheaper Much of the transcontinental traffic is now carried by satellites and optical fibers , but microwave relay remains important for shorter distances. Because the radio waves travel in narrow beams confined to a line-of-sight path from one antenna to the other, they do not interfere with other microwave equipment, so nearby microwave links can use the same frequencies.
Antennas must be highly directional high gain ; these antennas are installed in elevated locations such as large radio towers in order to be able to transmit across long distances. Typical types of antenna used in radio relay link installations are parabolic antennas , dielectric lens, and horn-reflector antennas , which have a diameter of up to 4 meters.
Highly directive antennas permit an economical use of the available frequency spectrum, despite long transmission distances. Because of the high frequencies used, a line-of-sight path between the stations is required. Additionally, in order to avoid attenuation of the beam, an area around the beam called the first Fresnel zone must be free from obstacles.
Obstacles in the signal field cause unwanted attenuation. High mountain peak or ridge positions are often ideal. Obstacles, the curvature of the Earth, the geography of the area and reception issues arising from the use of nearby land such as in manufacturing and forestry are important issues to consider when planning radio links.
In the planning process, it is essential that "path profiles" are produced, which provide information about the terrain and Fresnel zones affecting the transmission path. The presence of a water surface, such as a lake or river, along the path also must be taken into consideration since it can reflect the beam, and the direct and reflected beam can interfere at the receiving antenna, causing multipath fading.
Rare events of temperature, humidity and pressure profile versus height, may produce large deviations and distortion of the propagation and affect transmission quality. All previous factors, collectively known as path loss , make it necessary to compute suitable power margins, in order to maintain the link operative for a high percentage of time, like the standard Hop distance is the distance between two microwave stations.
During s microwave radio links begun widely to be used for urban links in cellular network. Furthermore, link planning deals more with intense rainfall and less with multipath, so diversity schemes became less used.
Another big change that occurred during the last decade was an evolution toward packet radio transmission. Therefore, new countermeasures, such as adaptive modulation , have been adopted. The emitted power is regulated for cellular and microwave systems. These microwave transmissions use emitted power typically from 0. In the last decade the dedicated spectrum for each microwave band has become extremely crowded, motivating the use of techniques to increase transmission capacity such as frequency reuse, Polarization-division multiplexing , XPIC , MIMO.
The first experiments with radio repeater stations to relay radio signals were done in by Emile Guarini-Foresio. In an Anglo-French consortium headed by Andre C. The radiated power, produced by a miniature Barkhausen-Kurz tube located at the dish's focus, was one-half watt. A military microwave link between airports at St. The development of radar during World War II provided much of the microwave technology which made practical microwave communication links possible, particularly the klystron oscillator and techniques of designing parabolic antennas.
After the war, telephone companies used this technology to build large microwave radio relay networks to carry long distance telephone calls. It was expected at that time that the annual operating costs for microwave radio would be greater than for cable.
There were two main reasons that a large capacity had to be introduced suddenly: Pent up demand for long distance telephone service, because of the hiatus during the war years, and the new medium of television, which needed more bandwidth than radio.
Remarkable were the microwave relay links to West Berlin during the Cold War , which had to be built and operated due to the large distance between West Germany and Berlin at the edge of the technical feasibility.
In addition to the telephone network, also microwave relay links for the distribution of TV and radio broadcasts. This included connections from the studios to the broadcasting systems distributed across the country, as well as between the radio stations, for example for program exchange.
Military microwave relay systems continued to be used into the s, when many of these systems were supplanted with tropospheric scatter or communication satellite systems. When the NATO military arm was formed, much of this existing equipment was transferred to communications groups.
The typical communications systems used by NATO during that time period consisted of the technologies which had been developed for use by the telephone carrier entities in host countries. The typical microwave relay installation or portable van had two radio systems plus backup connecting two line of sight sites. These radios would often carry 24 telephone channels frequency division multiplexed on the microwave carrier i.
Lenkurt 33C FDM. Any channel could be designated to carry up to 18 teletype communications instead. Similar systems from Germany and other member nations were also in use. Long-distance microwave relay networks were built in many countries until the s, when the technology lost its share of fixed operation to newer technologies such as fiber-optic cable and communication satellites , which offer a lower cost per bit.
By positioning a geosynchronous satellite in the path of the beam, the microwave beam can be received. At the turn of the century, microwave radio relay systems are being used increasingly in portable radio applications. The technology is particularly suited to this application because of lower operating costs, a more efficient infrastructure , and provision of direct hardware access to the portable radio operator. A microwave link is a communications system that uses a beam of radio waves in the microwave frequency range to transmit video , audio , or data between two locations, which can be from just a few feet or meters to several miles or kilometers apart.
Microwave links are commonly used by television broadcasters to transmit programmes across a country, for instance, or from an outside broadcast back to a studio. Mobile units can be camera mounted, allowing cameras the freedom to move around without trailing cables. These are often seen on the touchlines of sports fields on Steadicam systems. Terrestrial microwave relay links are limited in distance to the visual horizon , a few tens of miles or kilometers depending on tower height.
Tropospheric scatter "troposcatter" or "scatter" was a technology developed in the s to allow microwave communication links beyond the horizon, to a range of several hundred kilometers. The transmitter radiates a beam of microwaves into the sky, at a shallow angle above the horizon toward the receiver. As the beam passes through the troposphere a small fraction of the microwave energy is scattered back toward the ground by water vapor and dust in the air.
A sensitive receiver beyond the horizon picks up this reflected signal. Signal clarity obtained by this method depends on the weather and other factors, and as a result, a high level of technical difficulty is involved in the creation of a reliable over horizon radio relay link. Troposcatter links are therefore only used in special circumstances where satellites and other long-distance communication channels cannot be relied on, such as in military communications. From Wikipedia, the free encyclopedia.
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An Introduction to Microwave and Satellite Communication
Skip to content. Related Articles. Last Updated : 13 Feb, Terrestrial Microwave Transmission System TMTS : In these systems, the signals are extremely concentrated and the physical route must be line of sight. The signals in these systems are extended with the help of Relay towers. Terrestrial Microwave Systems need directional parabolic antennas to broadcast and receive signals in the lower gigahertz range. These systems need satellites which are in the geostationary orbit which is km above the earth.
Skip to Main Content. A not-for-profit organization, IEEE is the world's largest technical professional organization dedicated to advancing technology for the benefit of humanity. Use of this web site signifies your agreement to the terms and conditions. Satellite and terrestrial microwave communications in China Abstract: China deploys satellite communications, microwave radio links, and optical fiber systems as three major transmission infrastructures for its public switched telephone network PSTN. The deployment of the first two of these infrastructures, satellite communications and radio links, is described. Article :. Date of Publication: July
An Introduction to Microwave and Satellite Communication
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