Earth stations use microwave frequencies, which lie between approximately 1 and 30 GHz, and therefore owe much to the development of Radio Detecting and Ranging (RADAR) systems. Many readers are aware that a radar antenna in the Hawaiian Islands detected imperial Japanese aircraft that bombed Pearl Harbor on December 7, 1941 [3]. However, much earlier, in 1929, G. Ross Kilgore, an engineer at Westinghouse, generated 18 GHz of microwave energy with an experimental split-anode magnetronvacuum tube. This particular device could measure Doppler reflections from moving automobiles and railroad cars. Radar improved in RF power output and sophistication during World War II and shortly thereafter, providing a technology base for terrestrial and satellite microwave communications.
Professor Wilmer Barrow of the pioneering Radiation Laboratory at MIT experimented with electromagnetic horn antennas for static-less ultrahigh-frequency wave transmission. The system consisted of a conducting tube, a transmitting terminal device, and either a receiving terminal unit or the radiating horn. Other developments at the Rad Lab include a multitude of microwave components like the klystron, numerous waveguide devices like diplexers, and antenna systems for radar and communication applications. An early horn reflector antenna was developed at Bell Laboratories in 1942, a precursor to antennas used in terrestrial and satellite microwave communications. After the war, Raytheon used microwave technology in an innovative (and noncommunication) manner with their invention of the microwave oven. Not surprisingly, the first food item to be cooked was popcorn.
AT&T recognized that microwave technology could increase the capacity and reliability of long-haul communication lines. Line-of-sight microwave links were established across the developed regions of the world during the 1950s and 1960s. The terminal ends and intermediate connection points were very much like earth stations in their design and use, namely to interface the long-distance link with local users. The overall microwave network offers much that a modern ground segment can, although it is tied to the specific routing and associated real estate.
Radio astronomy, while not able to command the investment and revenues of commercial telephone and television services, still benefited from the availability of microwave technology. Here, the challenge is to receive very weak signals (effectively noise within the noise). The parabolic dish antennas grew in size to provide greater ability to discriminate distant radio emitters.
The principle behind this is that the width of the narrow antenna beam is inversely proportional to the diameter of the reflector. Thus, radio telescopes in the 30-to-100-m range soon appeared, topped by the giant 305-m Arecibo dish antenna in Puerto Rico (this antenna is actually constructed in a small lake basin and was featured in the James Bond movie Golden Eye). Constructed in 1960, and operated by Cornell University under a cooperative agreement with the National Science Foundation (NSF), the Arecibo radio telescope not only receives celestial noise, it can also transmit radar signals to map the planets of our solar system.
Radio telescopes more along the lines of earth stations were constructed at several locations in the United States and around the world. The 91-m (300-ft) Green Bank Telescope was constructed in the 1960s but experienced mechanical failure in 1988. At the time of this writing, another 100-m radio telescope was under construction, this time using the offset parabolic reflector design popular for home DBS installations (and many spacecraft reflector antennas as well). Another type of terrestrial radio communications system is the tropospheric scatter communication link, which employs microwave signals that can be propagated over the horizon (OTH).
The tropo installation shown in Figure 1.4 was installed in 1967 by the U.S. Army Signal Corps at Pleiku, Vietnam, where it provided a single-hop link of about 230 km to Nha Trang (four times line-of-sight range). As can be seen, this 15-m antenna points nearly at the horizon to acquire the relatively weak but reasonably stable) signals that have been dispersed by the troposphere.
Professor Wilmer Barrow of the pioneering Radiation Laboratory at MIT experimented with electromagnetic horn antennas for static-less ultrahigh-frequency wave transmission. The system consisted of a conducting tube, a transmitting terminal device, and either a receiving terminal unit or the radiating horn. Other developments at the Rad Lab include a multitude of microwave components like the klystron, numerous waveguide devices like diplexers, and antenna systems for radar and communication applications. An early horn reflector antenna was developed at Bell Laboratories in 1942, a precursor to antennas used in terrestrial and satellite microwave communications. After the war, Raytheon used microwave technology in an innovative (and noncommunication) manner with their invention of the microwave oven. Not surprisingly, the first food item to be cooked was popcorn.
AT&T recognized that microwave technology could increase the capacity and reliability of long-haul communication lines. Line-of-sight microwave links were established across the developed regions of the world during the 1950s and 1960s. The terminal ends and intermediate connection points were very much like earth stations in their design and use, namely to interface the long-distance link with local users. The overall microwave network offers much that a modern ground segment can, although it is tied to the specific routing and associated real estate.
Radio astronomy, while not able to command the investment and revenues of commercial telephone and television services, still benefited from the availability of microwave technology. Here, the challenge is to receive very weak signals (effectively noise within the noise). The parabolic dish antennas grew in size to provide greater ability to discriminate distant radio emitters.
The principle behind this is that the width of the narrow antenna beam is inversely proportional to the diameter of the reflector. Thus, radio telescopes in the 30-to-100-m range soon appeared, topped by the giant 305-m Arecibo dish antenna in Puerto Rico (this antenna is actually constructed in a small lake basin and was featured in the James Bond movie Golden Eye). Constructed in 1960, and operated by Cornell University under a cooperative agreement with the National Science Foundation (NSF), the Arecibo radio telescope not only receives celestial noise, it can also transmit radar signals to map the planets of our solar system.
Radio telescopes more along the lines of earth stations were constructed at several locations in the United States and around the world. The 91-m (300-ft) Green Bank Telescope was constructed in the 1960s but experienced mechanical failure in 1988. At the time of this writing, another 100-m radio telescope was under construction, this time using the offset parabolic reflector design popular for home DBS installations (and many spacecraft reflector antennas as well). Another type of terrestrial radio communications system is the tropospheric scatter communication link, which employs microwave signals that can be propagated over the horizon (OTH).
The tropo installation shown in Figure 1.4 was installed in 1967 by the U.S. Army Signal Corps at Pleiku, Vietnam, where it provided a single-hop link of about 230 km to Nha Trang (four times line-of-sight range). As can be seen, this 15-m antenna points nearly at the horizon to acquire the relatively weak but reasonably stable) signals that have been dispersed by the troposphere.
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