Defense Intelligence Reference Document Pulsed High-Power Microwave Source Technology

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Pulsed High-Power Microwave Source Technology
Summary
This paper provides an overview of the major types of high-power microwave
(HPM) sources and the critical technologies required to build them. Pulsed
HPM technology has been of scientific and military interest for several decades.
Originally, the interest focused on the area of high-altitude electromagnetic
pulse (HEMP) concerns.
HEMP is produced when a nuclear weapon is detonated high above the earth's
surface, creating gamma radiation that interacts with the atmosphere to
create an intense electromagnetic (EM) energy field that is harmless to people
as it radiates outward but can overload computer circuitry with effects similar
to, but causing damage more swiftly than, a lightning strike. HEMP effects
became fully known in 1962, when a high-altitude nuclear test (codenamed
"Starfish Prime") over the Pacific Ocean disrupted radio stations and
electronic equipment 800 miles away in Hawaii. The HEMP effect can span
thousands of miles, depending on the altitude, design, and power of the
nuclear burst. It is speculated that a single device detonated at high altitude
over the central United States could affect the entire country, since the HEMP
would be picked up by conductors, such as wires and power cables, acting as
antennas to conduct the electrical energy into various electronic systems. This
EM radiation was found to have field levels on the order of several hundreds of
kilovolts per meter with onset or rise times of a few nanoseconds and a
duration of nearly a microsecond. Fields of these magnitudes were found to
have severe detrimental effects on numerous electrical systems and items,
such as the power grid, automobiles, communications equipment, and aircraft.
Much testing was done in the 1960s and 1970s to determine vulnerabilities
and to find mitigation solutions. The HEMP is essentially a wideband
microwave pulse, and several EMP simulators were devised and built for use in
testing its effect on various electronic systems. In addition, several programs
were established to investigate the possibility of generating and radiating
other spectrums of EM radiation that may have some of these same effects
without requiring a nuclear detonation. This was the impetus for the
advancement of pulsed HPM technologies for weapons.
HPM radiation is composed of shorter waveforms at higher frequencies than is
HEMP, which makes it highly effective against electronic equipment and more
difficult to harden against. Whereas HEMP weapons are large in scale and
require a nuclear capability along with technology to launch high-altitude
missiles, HPM weapons are smaller in scale, involve a much lower level of
technology, and are within the capability of almost any state. HPMs can
damage computers and electronics similar to the way HEMP can, although the
effects are limited to a much shorter range. Technical accessibility, lower cost,
and the vulnerability of U.S. electronic equipment could make small-scale HPM
weapons attractive to terrorist groups. HPM devices are now categorized as
directed-energy weapons.
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