Entitled "High Power Microwaves: Strategic and Operational Implications for Warfare," it was published by the Air University's center for strategy and technology in early 2000.

Walling is now a division chief in Air Force Materiel Command at Wright-Patterson AFB, Ohio.

"The projected maximum capability for a microwave [armed] UCAV is approximately 100,000 pulses of microwave energy (or shots) per mission," Walling wrote. "If one assumes 1,000 pulses per target, it is conceivable that a microwave UCAV could attack on the order of 100 targets per mission. In addition, a microwave system could be used to protect the UCAV from enemy missiles [even] if the enemy has the ability to detect low-observable aircraft."

HPM also affects a larger area than a bomb, but without harming physical structures or people. A 1-ton bomb creates damage in a radius of about 120 ft. "The footprint of a microwave munition is at least 100 times greater than that of a conventional munition," the report states. That may be a bloated number if applied to developmental weapons currently available for use against Iraq, according to other U.S. officials. They usually describe effects in terms of a few thousand feet or less. In fact, the primary stumbling block for directed-energy weapons is achieving sufficient range and power levels to be effective.

U.S. MILITARY RESEARCH laboratories have demonstrated HPM effects ranging from upsetting to destroying the electronics within military and commercial systems, Walling noted. The paper's conclusion, made more than two years ago, is that "high-power microwave technology is ready for the transition to active weapons in the U.S. military."

Both Defense Secretary Donald H. Rumsfeld and the chief of U.S. Air Forces, Europe, Gen. Gregory Martin, have said publicly that unspecified new developmental weapons technology could be used in an attack on Iraq.

Facilities that manufacture, store or dispense chemical, biological and nuclear weapons are a "target set" particularly earmarked for energy weapons, according to statements made this summer and fall by U.S. aerospace industry officials. Conventional attacks could leave plumes of lethal agents adrift.

HPM devices have great potential both as offensive and defensive weapons, Walling said. She cited a 1998 Air Force survey--"Directed-Energy Applications for Tactical Airborne Combat"--that found the top four priorities were for microwave weapons (instead of lasers) in the areas of precision-guided munitions, large aircraft self-protection shields, small aircraft self-protection shields and as weapons for unmanned combat air vehicles. As a munition, some developmental systems are believed to be ready for combat in Iraq. Boeing plans to build an HPM weapon into the Block 30 version of its X-45 UCAV.

These weapons also could be built into a pod for carriage on a helicopter or packaged as artillery shells, scatterable mines and 1-ton bombs, the report said. As a defensive system, it contends HPM devices could ward off infrared- and radar-guided missiles. A phased-array antenna allows for rapid retargeting.

The report quickly ticks off the advantages of HPM weapons: They don't rely on exact knowledge of the enemy system. They leave persisting effects in enemy targets that may take weeks to find and repair. Even if enemy systems are turned off, they are still affected. And to counter HPM, the entire system must be hardened, which is a very expensive process.

An energy pulse can get into an enemy system by the "front door," which means its own antenna, dome or other sensor opening; or through the "back door," which includes cracks, seams, trailing wires, metal conduits of seals.

Once inside, the emissions can destroy or disrupt integrated circuits, circuit cards and relay switches. The system's own electronic circuitry transmits the pulse, and resulting damage, even deeper into the system.

In the microwave technical community, the ability to scale or increase the effects is often described as "dial a hurt," Walling said.

Results depend on the distance between the HPM weapon and the target, the vulnerability of the target, the power generated, and the characteristics of the microwave emission including frequency, burst rate and pulse duration. A rough scale describes four levels of effects:

* Deny, which involves electronic upset or jamming. It might cause malfunctions within relay and processing circuits.

* Degrade, which involves locking up a system or limiting its capabilities enough to require rebooting. It can include signal override or turning power on and off at irregular intervals.

* Damage, which includes permanent effects that "latch up" a system. This can mean damage to components, circuit cards or mother boards, as wells as weeks to diagnose and repair the problems. Because microwaves can enter through multiple entry points, it is likely numerous circuits and components will be damaged.

* Destroy, which means catastrophic and permanent injury to the system, requiring total replacement.

ANTENNA TECHNOLOGY is crucial for HPM weapons. Field of view for the phased-array emitter is expected to vary from several to tens of degrees. The multi-element design allows it to be built conformally into a pod or UCAV. Because it doesn't require precise aiming, there are far fewer stringent pointing and tracking requirements, Walling said. The microwaves' cone could offer a means to attack multiple targets at once; for example, all of the equipment in an antiaircraft missile site.

The range of HPM weapons has always been a concern. Tests have shown effects at tens to "more than" hundreds of feet. Walling seemed more optimistic. "With current technology, the range for a tactical microwave weapon could be in the tens of kilometers, and future advances . . . should permit the development of even longer ranges," the report said.

Other advantages cited for HPM weapons are that they would be immune to the weather and could produce multiple shots on a single mission. However, the report also alludes to single-shot designs. These latter seem to address concerns that side and back lobes from the generation of an HPM pulse could affect the carrying aircraft's own electronics.

Power levels for HPM weapons are increasing. The report said one microwave source weighing less that 45 lb. radiated 1 gigawatt of power within a few nanoseconds. A 400-lb. system radiated 20 gigawatts. The report noted that Hoover Dam generates 2 gigawatts per day. The HPM weapon would draw power from the air vehicle's engines, which would let it make a number of attacks during a mission.

USAF Acknowledges Beam Weapon Readiness
By David A. Fulghum/Aviation Week & Space Technology 04-Oct-2002