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MILITARY USE OF THE EMF SPECTRUM

 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

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frequencies and observe heat signatures of personnel, missiles, aircraft, artillery, and vehicles.

Other Applications

Militaries use the spectrum to target and potentially attack adversaries. Missiles in general, and anti-air munitions in particular, use either infrared or radar for terminal guidance (i.e., guiding a missile once it has been launched) to targets. Electronic jammers are used to deny an adversary access to the spectrum. These jammers are primarily used in the radio wave and microwave frequencies (and sometimes paired together), thereby preventing communications (both terrestrially and space-based) as well as radar coverage. Militaries have also begun using lasers to disable intelligence collection sensors, provide a potential kinetic kill against small unmanned aerial systems (aka “drones”), and communicate with satellites.

Types of Spectrum Operations

Numerous military operations use the spectrum. One type is command and control. Command and control uses all of these applications to develop a common operating picture and communicate the commander’s orders. Command and control is resourced according to a unit’s size and mission focus, from a few radios and computers for platoon- and company-level operations to specialized satellites and aircraft for joint operations such as nuclear command and control. Command and control aircraft, such as the E-8C Joint STARS, use communications systems and synthetic aperture radars to develop a comprehensive picture of the battlespace to direct ground forces to their most effective positions for countering enemy forces.

Electronic warfare uses the spectrum to gain and maintain military access to the spectrum. SIGINT capabilities allow military forces to understand where adversary forces are located as well as what frequencies they use for communications and radars. This intelligence, called electronic support by the military, is then used to develop an operational plan to jam (i.e., attack an adversary’s use of the spectrum) radio frequencies. Using SIGINT capabilities on their own forces, militaries can develop techniques to protect themselves from attacks.

Low observable weapons systems manipulate the spectrum to reduce their electromagnetic signature—such as radar return, radio emission, and even heat. This can range from reducing a radar signature, to creating narrow radio beams to reduce the probability of detection or intercept, to reducing spectrum emissions entirely. These design approaches can be used in ships (e.g., Zumwalt-class destroyer), aircraft (e.g., the B-2 Spirit and the F-35 Lightning II), and radar systems (e.g., the AN/APG-81 actively electronically scanned array radar).

Congressional Interest in the Spectrum

Congress has actively supported the deployment of fifth generation (5G) technologies, identifying spectrum used for 5G, and amending federal rules and regulations to facilitate deployment of 5G infrastructure. The Federal Communications Commission is auctioning spectrum for 5G, which DOD currently uses for satellite communications and weather radars. Auctioning this part of the spectrum

would potentially eliminate DOD’s ability to use these systems. DOD could use funds from these auctions, through the Spectrum Relocation Fund, to develop new technologies and relocate displaced technologies to a new place on the spectrum.

Congress has also recently passed legislation impacting the military’s use of the spectrum, particularly in terms of spectrum allocation and electronic warfare. Recent congressional actions in the National Defense Authorization Acts (NDAAs) include the following:

 FY2017 NDAA. Section 234 authorized the Secretary of Defense to create a pilot program to modernize and field spectrum warfare systems. Section 240 required DOD to develop an electronic warfare strategy. Section 1044 protected certain federal spectrum operations.

 FY2018 NDAA. Section 1697 authorized the Secretary of Defense to establish a pilot program to assess the viability of mapping DOD’s usage of the spectrum. Section 1608 required the Secretary of the Air Force to submit a report on the plans using transaction authority to acquire commercial satellite bandwidth.

 FY2019 NDAA. Section 255 required DOD to perform an independent assessment of current electronic warfare plans and programs. Section 1053 directed the Secretary of Defense to establish process and procedures to “develop, integrate and enhance electronic warfare mission area and the conduct of joint electromagnetic spectrum operations in all domains across the Department of Defense and ensure that such processes and procedures provide for integrated defense-wide strategy, planning, and budgeting with respect to the conduct of such operations.”

Defense Primer: Military Use of the Electromagnetic Spectrum

   Relevant Statutes

Title 10, U.S. Code, Armed Forces, Section 488: Management and review of electromagnetic spectrum

      CRS Products

CRS In Focus IF11118, Defense Primer: Electronic Warfare, by John R. Hoehn

CRS In Focus IF11493, Defense Capabilities: Joint All Domain Command and Control, by Nishawn S. Smagh

      Other Resources

DOD Instruction 4650.01. Policy and Procedures for Management and Use of the Electromagnetic Spectrum. Incorporating Change. 1 Oct 17, 17

DOD Instruction 3222.03. DOD Environmental Effects Program Incorporating Change. 2 Oct 10 17

Joint Pub. 6-01 Joint Electromagnetic Spectrum Management Operations

     https://crsreports.congress.gov

John R. Hoehn, Analyst in Military Capabilities and Programs

Defense Primer: Military Use of the Electromagnetic Spectrum

 IF11155

 Disclaimer

This document was prepared by the Congressional Research Service (CRS). CRS serves as nonpartisan shared staff to congressional committees and Members of Congress. It operates solely at the behest of and under the direction of Congress. Information in a CRS Report should not be relied upon for purposes other than public understanding of information that has been provided by CRS to Members of Congress in connection with CRS’s institutional role. CRS Reports, as a work of the United States Government, are not subject to copyright protection in the United States. Any CRS Report may be reproduced and distributed in its entirety without permission from CRS. However, as a CRS Report may include copyrighted images or material from a third party, you may need to obtain the permission of the copyright holder if you wish to copy or otherwise use copyrighted material.

https://crsreports.congress.gov | IF11155 · VERSION 5 · UPDATED

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