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Microwave Antennas and Microwave Networks

University of Oxford_061422E
[University of Oxford]

- Microwave Link Networks

A microwave link is a communication system that uses beams of radio waves in the microwave frequency range to transmit information between two fixed locations on Earth. They are critical to many forms of communication and impact a wide range of industries. 

Broadcasters use microwave links to send programs from the studio to transmitter locations that may be miles away. Microwave links carry cellular telephone calls between cell sites. Wireless Internet service providers use microwave links to provide their customers with high-speed Internet access without the need for cable connections. 

Telephone companies carry calls between switching centers over microwave links, although they have recently been largely replaced by fiber-optic cables. Companies and government agencies use them to provide communication networks between nearby facilities within an organization, such as a company with multiple buildings within a city. 

One of the reasons microwave links are so adaptable is that they are broadband. This means they can move large amounts of information at high speeds. Another important characteristic of microwave links is that they do not require any equipment or facilities between the two termination points, so installing microwave links is usually faster and less costly than cable connections. 

Finally, they can be used almost anywhere as long as the distances spanned are within the operating range of the device and there is a clear path between locations (i.e. no solid obstructions). Microwaves are also able to penetrate rain, fog and snow, meaning inclement weather won't interrupt transmissions.


- Microwave Antennas

A microwave antenna is a physical transmission device used to broadcast microwave transmissions between two or more locations. In addition to broadcasting, antennas are also used in radar, radio astronomy and electronic warfare. Microwave transmission is the transmission of information by microwave radio waves. 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.

There are different types of microwave antennas that are proven critical in any microwave network. While many types are available to meet different mechanical and electrical requirements, the most common type used for terrestrial microwave networks is the parabolic. However, there are also less frequently used such as the dielectric lens, flat panel, horn, sector, and Yagi. Each one is suitable for specific situations and systems. 


- Types of Microwave Transmission

There are two types of microwave transmission, which are as follows.

  • Terrestrial Microwave Transmission Systems (TMTS): In these systems, signals are so concentrated that physical routing must be within line of sight. The signal in these systems is extended with the help of repeater towers. Terrestrial microwave systems require directional parabolic antennas to broadcast and receive signals in the lower gigahertz range.
  • Satellite Microwave Transmission System (SMTS): A satellite microwave transmission system uses satellites to broadcast and receive signals. These systems require satellites in geostationary orbit at 36,000 kilometers from Earth. These satellites operate as repeaters, with receiving antennas, transponders, and signal transmission.


Satellite Microwave Communication_052123A
[Satellite Microwave Communication - Tutorialspoint]

- Microwave Transmission Networks

Microwave transmission is the use of electromagnetic waves within the microwave frequency range of 300MHz to 300GHz (1 meter to 1 millimeter wavelength) in the electromagnetic spectrum for information transmission. Microwave signals are usually limited to line-of-sight, so using these signals for long-distance transmission requires a series of repeaters to form a microwave relay network. Microwave signals can be used in beyond-horizon communications using troposcatter, but such systems are expensive and typically only used in professional roles.

The use of the microwave spectrum has exploded in recent years by new telecommunications technologies such as wireless networks and direct broadcast satellites that broadcast TV and radio directly to consumers' homes. Larger line-of-sight links are again popular to handle connections between mobile phone towers, although these links are not usually organized into long relay chains.

Wireless microwave transmission of information:

  • Utilizes communication satellites for one-way and two-way communication
  • Terrestrial microwave relay links in telecommunications networks, including backbone or backhaul carriers in cellular networks

More recently, microwaves have been used for wireless power transfer.


- Applications of Microwave Transmission

Microwaves are widely used for point-to-point communications because their small wavelengths allow appropriately sized antennas to direct them into narrow beams that can be pointed directly at a receiving antenna. This allows nearby microwave devices to use the same frequency without interfering with each other like low-frequency radio waves do. This frequency reuse saves scarce radio spectrum bandwidth. 

Another advantage is that the high frequency of microwaves gives the microwave band a very large information-carrying capacity; the bandwidth of the microwave band is 30 times wider than that of all other radio spectrum below it. The downside is that microwaves are limited to line-of-sight propagation; they cannot go around hills or mountains like low-frequency radio waves can. 

Microwave radio transmissions are commonly used in point-to-point communication systems on the Earth's surface, satellite communications, and deep space radiocommunications. Other parts of the microwave radio band are used for radar, radio navigation systems, sensor systems and radio astronomy. 

The next higher band of the radio spectrum, between 30 GHz and 300 GHz, is called "millimeter wave" because their wavelengths range from 10 mm to 1 mm. Radio waves in this band are strongly attenuated by gases in the atmosphere. This limits their actual transmission distance to a few kilometers, so these frequencies cannot be used for long-distance communication. The electronics required for mmWave are also at an earlier stage of development than for microwave.



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