The US military has given the first public display of what it says is a revolutionary heat-ray weapon to repel enemies or disperse hostile crowds.

The gun - called Silent Guardian - projects an invisible high energy beam that produces a sudden burning feeling, but is actually harmless.

The beam can be fired as far as 500m (550 yards), much further than existing non-lethal weapons like rubber bullets.

The gun should be in use by the US military within three years.

The prototype weapon uses a large rectangular dish mounted on a Humvee vehicle.

The waves can penetrate clothes but not walls, suddenly heating up the skin of anyone in its path to 50C.

Journalists who volunteered to be zapped during the demonstration on an air base in the US state of Georgia described the sensation as similar to a blast from a very hot oven - too painful to bear and forcing them to dive for cover.

Military officials say the so-called "active denial system" is harmless, but could prove invaluable in the increasingly complex situations they face.

The marine colonel in charge said it was an alternative to going straight from shouting to shooting and could save lives.

The system could be used both for dispersing hostile crowds during peace time, or in conflicts like Iraq and Afghanistan.

James Westhead
BBC
25 January 2007, 05:58 GMT

Light Boosts Destructive Power of Microwave Weapons, Sensors

By David A. Fulghum

Electronic warfare is becoming less a science of developing new
technologies and more a process of sensor fusion, target networking and
finding new ways to manipulate existing tools of the trade. A case in
point--lasers and high-power microwave devices long have been eyed as
competing directed-energy attack options. However, researchers are now
combining the two to produce smaller, cheaper, more powerful, nonkinetic
weapons. Electronic attack has taken a new path as well, shifting from
covering enemy emissions with noise to finding, penetrating and
exploiting enemy networks from low-power cell-phone networks to
sophisticated air defense systems. The following articles explore some
of those changes.

High-power microwave weapons may be on the verge of a high-speed turn
toward the practical.

An advanced concept, pioneered by BAE Systems' researchers, uses light
to multiply the speed and power at which HPM pulses--powerful enough to
destroy enemy electronics--can be produced without the need for
explosives or huge electrical generators.

Researchers predict leaps of 10-100 times in power output within two
years. That advance could push the beam-weapon technology far beyond the
1-10-gigawatt limit of current tactical-size HPM devices. Long-standing
industry estimates are that it would require a 100-gigawatt pulse for a
few nanoseconds to disable a cruise missile at a useful range.

BAE Systems is not alone in the chase. Northrop Grumman and Raytheon are
also building distributed array radars that can produce air-to-air and
surface-to-air HPM weapons effects, contend longtime Pentagon radar
specialists. In particular, the F-22, F-35, F/A-18E/F and newest F-15
radars are designed to accept modifications that would focus their beams
to produce HPM energy spikes powerful enough to disable cruise,
anti-aircraft, air-to-air and emitter-seeking missiles. Germany's Diehl
is developing suitcase-size HPM devices that could be placed
surreptitiously in a target building to damage electronics such as
computers.

In addition, the U.S. military is giving classified briefings on the
threat of HPM weapon technologies being developed in China and Russia.
The Russians are believed to be developing radio-frequency microwave
weapons for air defense, and the Chinese are developing HPM and
electromagnetic pulse weapons for information warfare.

However, BAE Systems researchers claim they have made a singular leap in
HPM weapons technology by combining the use of lasers and radar-like
microwaves. Furthermore, the technology is scalable through the use of
4-in.-square arrays, each an integrated structure of dielectrics and
electrical conductors. One hundred of them distributed over a square
meter, for example, can generate up to 10 gigawatts of power, says
Robert D'Amico, BAE Systems' director of advanced programs.

"We have shown everything we claimed with a laboratory testbed," says
Oved Zucker, director of photonics programs for BAE Systems' advanced
concepts facility here. "We are in the process of demonstrating total
power substantially above 10 gigawatts, and we have plans to test [the
system]further in an airborne mode.

"The power bandwidth product--how much power and how fast you manipulate
it--is potentially the largest of any technology around. Having the
bandwidth with larger power is where the money is," he says. There's no
dearth of missions for HPM technology, including detecting and
detonating improvised explosive devices, finding suicide bombers or
hidden explosives, and attacking shoulder-fired anti-aircraft missiles.

There's also the appeal of weapons that can rob a foe of communications,
power and mobility--while largely eliminating collateral damage to
people and structures--which is a high priority for the U.S. military.

The development of HPM weapons has been hobbled for the last 30 years by
seemingly intractable cost, size, beam-control and power-generation
requirements. Tests of modified air-launched cruise missiles carrying
devices to produce explosively generated spikes of energy were
considered big disappointments in the early 1990s because of an
inability to direct pulses and predict effects. New active
electronically scanned array (AESA) radars can jam emitters or possibly
cause damage to electronic components with focused beams. But power
levels and ranges are limited by aperture size.

BAE Systems' photonically driven technology could open the way to much
smaller and more powerful electronic jammers, nonkinetic beam weapons
for cruise and anti-ship missile defenses, and stealth-detecting sensors.

"You could put a [sensor] system on a fighter-size aircraft that could
generate enough power, with a 1-ft. resolution, to see stealthy objects
at 100 mi." D'Amico says. "You can defeat stealth with enough power. If
stealth takes the signature [of an aircraft or missile] down a factor of
10, you have to increase the [sensor's] power by a factor of 10." Most
current fighter-size radars have less than a megawatt of peak power.
Detecting stealth would require tens of gigawatts, which is now
impossible in fighter-size packages.

What effects can HPM produce as an electronic warfare weapon?

"At one end, it can fry anything [electronic] that's out there," Zucker
says. "The levels of EW extend from the sledgehammer to just making the
[computer's] brain a little bit befuddled so it can't think for a
moment. At a lower level, you can kill the detector of the other guy's
radar as part of the suppression of enemy air defenses. You don't need
much power because you're going after the most sensitive part. You're
blinding the system."

The level below that is to momentarily stop electronics from
functioning. A radar will try to defend itself by using a chain of
circuits to "blink," and thereby shut out intruding signals. One method
of exploitation is to do something during the blink. But if an intruding
signal is fast enough, the radar can't react in time to keep out the
invader.

"You can put energy in there and it won't be able to respond," Zucker
says. "Another low-level effect is to make the computer skip bits so
that it's not processing efficiently for the moment. All these games
have to do with how much power [can be applied] and how fast."

BAE researchers envision HPM pulse weapons that are powerful enough to
disable a tank, a missile, perhaps a helicopter or aircraft, but at the
same time are small and light enough to function as part of a microwave
radar sensor designed into the skin of an aircraft.

Alternatively, the HPM weapons could be scaled up to shipboard
size--perhaps 100 sq. meters--to produce terawatt-size energy pulses.
That's theoretically a large enough energy spike to stop another ship.

"You kill the brains by aiming at the bridge area because of all the
computers and control systems there that run the ship," Zucker says.

This brute-strength scaling up of the technology involves installing a
distributed array on the side of a ship. The elements would work
together to form a large virtual antenna and then pull enough power from
the ship's electric engines to concentrate a beam on vulnerable areas.
From a few hundred yards, predictions are that the energy
spike--focused in a beam several feet wide--could disable all the
electrical equipment, including propulsion, leaving the ship a darkened,
drifting hulk.

Researchers have some unusual techniques in mind for the associated
antenna arrays.

"We are integrating a large number of transverse electromagnetic [TEM]
apertures," to produce the distributed transmitter arrays, he says. "To
produce a large number of TEM antennas is sensible only if you can make
each one sing to the same tune through this coherence [or
synchronization] that comes from using [the speed of] light. That allows
us to spread the source [of HPM pulse production] across the whole wing
of an airplane. Moreover, TEM doesn't have a cutoff frequency, which
gives us flexibility."

Because the high-speed switches modulate the HPM, they match the
circuitry to the antenna. Composite skins for fuselages could have the
conductors and switches built into them. At the moment, BAE is looking
at new, 20-cm.-thick aircraft wings, tapered at the leading and trailing
edges, with imbedded antenna structures instead of using a bolt-on system.

"That is my radiator, and it is a phased array," Zucker says. "It can be
a radar, communications, receiver or HPM transmitter. The wing is the
source with more gain than any aperture that's been available before. I
don't have to pump the energy through wave guides. More area means more
power and gain. Instead of megawatts, we're talking about gigawatts of
peak power."

Researchers say the antennas, photoconductive switches and transformer
blocks can be built into conformal skins for unmanned combat aircraft as
well. Unmanned designs are favored initially because of the vagaries in
distribution of HPM side lobes, the effects of HPM on humans, and the
disturbances that energy spikes can create in fly-by-wire flight control
systems.

Zucker also is designing fly-by-light flight control systems for UAVs.
With fly by light, actuators are triggered by simple blobs of light that
can't be disrupted by spikes of electrical energy produced by the
aircraft's payload.