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1 1 (August 21, 2020)

handle is hein.crs/govdblg0001 and id is 1 raw text is: 01;0$S~l i~s $ch$e Updated August 21, 2020 Defense Primer: Military Use of the Electromagnetic Spectrum Since the introduction of the two-way radio in the early 1900s, militaries have been interested in the electromagnetic spectrum (the spectrum). The proliferation of spectrum-dependent systems in all military domains-air, land, sea, space, and cyberspace-along with Department of Defense (DOD) concepts, such as net-centric warfare and multidomain battle, increases the military's dependence on the spectrum. What is the Spectrum? The electromagnetic spectrum is a series of frequencies ranging from radio waves to microwaves, visible light, X- rays, and gamma rays. As the wavelength of the electromagnetic radiation shortens, the waves have a higher frequency how quickly electromagnetic waves follow each other-and therefore more energy. Figure I. The Electromagnetic Spectrum Source: https://imagine.gsfc.nasa.gov/science/tool box/ emspectrumlI.html. Different parts of the spectrum serve different military purposes. Radio transmissions have relatively low data rates-particularly in the very low frequency range. However, they are able to travel long distances and pass through solid objects like buildings and trees, and are often used for communications equipment. Microwaves have higher throughput-ata upload and download rates-than radio waves and therefore are able to transmit more data, but are more limited in range and can be disrupted by solid objects. Hence, microwaves are often used for radars and satellite communications. Infrared waves, which emit energy, can be used for intelligence and targeting data because they are closely associated with heat sources. X- rays are routinely used for aircraft maintenance to identify cracks in airframes. Finally, gamma rays are high-energy radiation and help identify potential nuclear events. The following discussion focuses on the DOD's use of the radio wave, microwave, and infrared aspects of the spectrum. Applicatio~ns\ of theSetu The military uses the entire spectrum to support intelligence and military operations. These applications range from using very low frequency radio waves to communicate with submarines underwater, to microwaves as a continuous datalink between aircraft, and to lasers in the infrared and ultraviolet ends of the spectrum to dazzle satellite sensors and destroy drones. The majority of military communications capabilities use radio waves, microwaves, and infrared frequencies. Nearly every modern weapons system airplanes, satellites, tanks, ships, and radios- depends on the spectrum to function. These applications can be combined to provide an overall military capability, such as command and control or electronic warfare. The following discussion provides a few examples of spectrum applications. Military commanders have become accustomed to communicating with their forces near-instantaneously. Communication includes a range of options from low bandwidth options, such as transferring small strings of text, to high data-intensive applications, such as full motion video and video teleconferencing. Radio frequencies are the primary mechanism to transmit this data. These systems can be located terrestrially (either with ground forces or on ships), in the air, or in space (i.e., on satellites). In general, communications systems use radio and microwave frequencies; however, emerging communications technologies use lasers-transmitting light, instead of radio waves, between antennas. Radios use different frequencies depending on the range and amount of data they are required to transmit. Ground- based radios are typically used at short ranges, limited by the line of sight. These short ranges span no more than 50 miles. In general, militaries use satellites to communicate over longer distances. Situadonal Awarenezss Another application of the spectrum is using radio or microwave frequencies to develop a picture of the battle space by providing the location of friendly and enemy forces. The most common application is radar, however recently light detection and ranging (LIDAR) systems are also used. Both technologies send out a signal that is then reflected back to sensors to determine the distance, speed, and potentially altitude of an object. Radars operate on different radio and microwave frequencies, depending on their purpose. Lower-band frequencies provide a larger picture of the battle space, although, due to the amount of clutter or radar return (how much radio signal is returned to the radar), these systems are not able to provide target- quality pictures. Higher-band frequencies provide target- quality pictures, yet lack the same effective range. Radar and LIDAR systems are commonly associated with air defense, military aviation, artillery, and space systems. Signals intelligence (SIGINT) systems primarily collect spectrum emissions. These passive systems-that is, they do not emit their own signal-can listen to radio and radar mppm qq\ p\w gn'a', ggmm a 'S I 11\111WILiN,

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