https://crsreports.congress.gov
Updated April 10, 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 1. The Electromagnetic Spectrum
Source: https://imagine.gsfc.nasa.gov/science/toolbox/
emspectrum1.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—data 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.
Applications of the Spectrum
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.
Communications
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.
Situational Awareness
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
