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The Evolution of Directed Energy Weapons


With the rapid escalation of drones in warfare,the need for directed energy (DE) weapons, i.e., high-energy laser (HEL) and high-power microwave (HPM) systems, has become acute, as they may be the only cost-effective way of degrading or destroying drones, especially if they’re launched in swarms. Although laser DE weapons have significant strengths, this article focuses on HPM DE weapons that serve the same purposes but deliver their results differently.

The most mature HPM systems today are based on vacuum electronics (typically traveling-wave tubes), and their RF emissions consist of a high-intensity pulse of electromagnetic energy with a specific central frequency, a finite bandwidth around that central frequency, and a duty cycle. As high-power vacuum-tube-based technologies are typically quite large, they are ground- or ship-based systems with large high-gain antennas that focus their energy at ranges of effectiveness of about 1 km.

Larger, ground-based HPM systems have demonstrated a range of effectiveness of tens of kilometers for defense against aerial threats, such as missiles with RF seekers. Because RF seekers are very sensitive, an HPM weapon can easily damage their electronics, increasing the missile-targeting system’s probable circular error and causing them to fail to find or track an intended target. That said, HPM DE systems using GaN-based amplifiers are emerging that have significant advantages over their TWT counterparts.

Two Thousand Years Ago, Archimedes Has An Epiphany

Although DE weapons are considered a modern technological invention, it was Greek mathematician and scientist Archimedes who could claim credit for getting there first. He is claimed to have used an array of mirrors to magnify and focus the Sun’s rays to set fire to an invading Roman fleet during the siege of Syracuse in 214 B.C. (Figure 1). Two millennia later, the debate continues over who should take credit for the heat ray, whether Archimedes did what he said, and if so, whether it would have worked.

For example, in 1973, Greek scientist Ioannis Sakkas conducted an experiment at the Skaramagas naval base outside Athens. Greek sailors held up 70 mirrors, each with a copper coating and measuring 5 x 3 ft. The mirrors were pointed at a plywood mock-up of a Roman warship at around 160 ft. When the mirrors were focused accurately, the ship burst into flames within a few seconds, and Sakkas said that, in his opinion, he had no doubt that Archimedes could have used bronze mirrors to destroy Roman ships.

Figure 1 — Artistic interpretation of Archimedes’ mirror used to burn Roman ships. Source: Painting by Giulio Parigi, c. 1599, Wikipedia.

More recently, beginning in 2004 and again in 2014, the Discovery Channel’s MythBusters team conducted a similar experiment that, although not wholly verifying the performance of the approach, still caused part of a ship mockup to ignite (at least on a clear day). In 2014, the team performed the test again, this time with 500 schoolchildren holding mirrors aimed at a plywood model of a Roman ship 400 ft. away. The ship failed to reach a temperature (about 410° F) that would cause its plywood to ignite. They considered the approach “busted,” noting that Archimedes mirrors might have blinded the sailors but could not have set a ship afire.

Back to Modern Times

The U.S. has been researching HPM DE weapons since the 1960s, with the first efforts emerging from observations of the electromagnetic pulse triggered when nuclear weapons were detonated in the atmosphere 250 miles above the Pacific in 1962. In the aftermath, scientists noted that the blast caused a significant imbalance of electrons in the upper atmosphere. They interacted with the Earth’s magnetic field to create oscillating electric fields called electromagnetic pulse or EMP over a large area. They were so intense they damaged electronics in Hawaii, a thousand miles away.

Over the years, significant strides have been made in enhancing the power, range, and reliability of HPM DE weapons with improved beam control, RF output power output, more efficient power supplies, and better thermal management. Despite their limitations, interest and investment in DE technology continued in the 1980s, specifically as an element of the Reagan administration’s Strategic Defense Initiative (SDI) or “Star Wars” program.

Figure 2 — The Raytheon Active Denial System operates at 95 GHz and was designed to provide a non-lethal means of crowd control. Source: Raytheon

While unsuccessful (and chided as being absurd), the program represented a commitment to pursuing directed energy technology. After the 9/11 attacks, there was speculation regarding the role DE weapons would play in the so-called “Global War on Terror.” However, no system had yet achieved the cost efficiency or technological maturity to enable its use and some high-profile programs were canceled. Nevertheless, testing continued.

One of the more controversial and widely publicized results was the Active Denial System (ADS), shown in Figure 2, a non-lethal directed-energy weapon designed for area denial, perimeter security, and crowd control.  It was initiated by the Air Force Research Laboratory and created by Raytheon in 2010. Harking back to Archimedes, it was initially called a heat ray, as it works by heating the skin to the point where it becomes too uncomfortable to remain in place. Since then, it has been explored by various state and government agencies, including the Los Angeles Sheriff’s Department, which conducted an operational evaluation to stop or lessen the severity of inmate assaults.

According to available sources, it was never deployed, and for good reason: ADS works by firing a 100-kW beam at 95 GHz at the target and works on the same principle as a microwave oven, exciting the water and fat molecules in the skin, and instantly heating them via dielectric heating. The frequencies by ADS only penetrate the top layers of skin, with most being absorbed only up to 0.4 mm deep.

Figure 3 — The effects of HELs versus HPM DE weapons. Source: Directed Energy Weapon Supply Chains: Securing the Path to the Future, National Defense Industrial Association, 2024.

However, the effects of ADS occur when the temperature rises above 111° F, which leaves little room for error because first-degree burns occur at about 124 °F and second-degree burns occur at about 136 °F. If someone is wearing glasses or contact lenses, the glass can have the same effect as Archimedes’ heat ray, amplifying the intensity (and thus the temperature) of the energy, potentially causing severe burns. In short, while ADS seemed at the time like a great solution, the more the public was exposed to it (CBS News aired a segment about ADS in March 2008 on 60 Minutes), the more obvious it became that although it was designed to be “non-lethal,” the results might be the opposite.

Types of HPM DE Weapons

Two primary types of HPM weapons are being developed by DoD, CW and pulsed. CW HPMs deliver a constant stream of microwave energy in a wide area and are best suited for area denial operations against personnel or small electronics, like unmanned aerial systems (UAS). In contrast, pulsed-wave HPMs deliver high-power, short-duration pulses of energy that provide high levels of accuracy. HPMs can either degrade or destroy the electrical components of a target and are well-suited for offensive and defensive operations.

The interest in protecting U.S. military and civilian infrastructure increased as power, communications, and emergency and industrial systems, became controlled by digital electronics. The potential that an adversary could attack these systems became an increasing concern. The asymmetric threat in which large numbers of cheap weapons (i.e., drones) in a swarm could overrun a few sophisticated weapons raised alarms throughout DoD. DE, with its speed-of-light propagation and deep (and cheap) magazine, rose once again to a more prominent position for funding, and the Joint Program Office for Special Technology Countermeasures (JPO/STC) at the Naval Surface Warfare Center Dahlgren Division conducted intensive work on the vulnerability of digital systems to RF attack. The program also established a DoD-wide database of vulnerability data, source designs, and RF effects.

Figure 4 — Raytheon’s PHASER DE system can destroy multiple targets simultaneously. Source: Raytheon

In the late 1990s and early 2000s, Dahlgren initiated programs regarding the potential for RF attack using non-kinetic disruption, developed RF payloads for UAVs and demonstrated their effectiveness in field tests. It was DoD’s first demonstration of this type of HPM technology. To evaluate them, two multistory buildings were reconfigured to reflect different types of building construction and electromagnetic shielding.

HPM weapons have the benefits of a large firing capacity, low cost per shot, rapid engagement times, and a graduated response capability. They can destroy unshielded military and commercial electronic systems, which makes them effective at countering major asymmetric threats such as drone swarms. Some HPMs deliver energy at frequencies that target specific electronic systems that make it possible to limit physical and electronic collateral damage in highly populated urban environments. HPMs are also far less vulnerable than HELs to atmospheric disturbances, allowing them to be used in various environments.

Despite their many advantages, HPMs also have unique limitations. For example, the wide HPM “cone” (Figure 3) rapidly disperses and loses effectiveness over distance, making these weapons ill-suited for engaging targets such as hypersonic missiles or aircraft. Sometimes, HPMs can damage nearby friendly equipment, necessitating extra precautions to shield potentially vulnerable assets. And the absence of visible damage to a targeted system may leave commanders unsure if a target’s capabilities have been sufficiently degraded or destroyed. This uncertainty may make officials reluctant to rely solely on HPMs until reliable battle damage assessments can be determined.

Traditionally, laser and HPM DE systems concentrated on destroying electronic systems, their host, or both, but in the case of drones, drone swarms, or other targets, what’s required is to confuse the electronics or render them inoperable. Incinerating them is unnecessary, which means that an HPM system doesn’t necessarily need to transmit gigawatts of power to destroy a single target as it would against other assets, but only what’s needed to render it inoperable or send it off course.

Figure 6 — HiJENKS is the successor to CHAMP and uses smaller and more rugged HPM technology that can be integrated into a broader range of carrier systems. Source: U. S. Air Force

This capability has been demonstrated in one form or another for over 15 years since Raytheon developed its Valiant Eagle system in 2006, which was designed to create an invisible microwave dome around an airport that could block missiles heading toward incoming and outgoing aircraft. Later systems include BAE Systems Bofors HPM Blackout is composed of an integrated pulsed power unit, a microwave source, and an exchangeable conical horn antenna. Support systems include a compact battery-powered vacuum system for the microwave tube and a gas supply system for the pulsed power unit. The integrated battery supply makes the system operational in all terrains and independent of standard laboratory utilities. The system’s total weight is less than 500 kg, and the length is just above 2 m.

More recently, Raytheon’s PHASER DE system (Figure 4) was awarded by Dahlgren a three-year $31.3 million contract to deliver prototype equipment to the US Navy and Air Force as part of the Directed Energy Front-line Electromagnetic Neutralization and Defeat (DEFEND) program. Rather than burning up the target, PHASER transmits high levels of RF energy to a reflector antenna and can destroy multiple targets simultaneously. The conical nature of the beam means that a single pulse can attack several drones in midair at once.

Another system in advanced development, the Tactical High-power Operational Responder (THOR), has demonstrated the ability to disable more than 100 drones simultaneously, is powered from a standard AC system, and stows in a 20-ft. transport container that can be transported in a C-130 (Figure 5). The system can be set up within 3 hr., with a user interface requiring minimal user training. The overall cost to develop the technology was about $18 million. AFRL is also progressing on a more advanced version of THOR to threaten military bases and has spent $15 million to develop it with BAE Systems, Leidos, and Verus Research. The next-generation platform is named Mjölnir as an homage to the mythical god Thor’s hammer. AFRL has awarded Leidos a $26 million contract to develop and deliver the Mjölnir prototype sometime this year.

The Counter-electronics High Power Microwave Advanced Missile Project (CHAMP), demonstrated by Boeing and AFRL, uses the body of an AGM-86 Conventional Air Launched Cruise Missile (CALCM) to carry a payload that uses microwave pulses to disable electronic devices. It was developed over the past two decades at AFRL and can reportedly deliver 100 shots per sortie. Raytheon has also demonstrated a ground-based air defense high-powered microwave system derived from CHAMP.

The High-Powered Joint Electromagnetic Non-Kinetic Strike Weapon, known as HiJENKS (Figure 6), also uses microwave technology to disable an adversary’s electronic systems. HiJENKS is the successor to CHAMP and uses smaller and more rugged HPM technology that can be integrated into a broader range of carrier systems.

The most recent and potentially most impressive development uses GaN-based RF power amplifiers rather than vacuum tubes to generate the RF power and an active phased array. The system, called Leonidas (Figure 7), was developed by Epirus, founded in 2018, with facilities in Los Angeles and McLean, VA. While tube-based HPM technologies can be the size of a shipping container, Leonidas can fit in the backup of a pickup truck.

Figure 7 — The Epirus Leonidas system is the first to use solid-state (GaN) rather than vacuum-tube technology. Source: Epirus

Like an AESA system, Leonidas uses beam steering to focus its energy on a target or targets while defining no-fly zones to allow friendly forces to continue operating. Leonidas can fire thousands of “rounds” per second. Leonidas has an open systems architecture, relies on online-replaceable amplifier modules, and rapidly fires a barrage of unique waveforms to exploit the frequencies that make a UAS target susceptible.

Ukraine could use all the systems right now, but that seems unlikely, even though the threats from Russia would be a perfect beta test for them. THOR and PHASER have been employed for this purpose in several countries, while Leonidas has not. For those who remember, it was a situation like this that forced GaN into service for the first time in the mid-2000s for use in countering the IEDs that were taking their toll on Humvees in Iraq. So, perhaps there is hope that these systems will be thrust into the fray because they could make a significant difference in the war’s outcome.

Chinese and Russian HPM Programs

China has been developing DE weapons since at least the 1980s and continues to make advancements. While many reports regarding technical success are undoubtedly exaggerated, China is surely making efforts to expand and improve its directed energy capabilities, including HPM weapons. Reports indicate that China has developed the WB-1, an anti-personnel area-denial system like ADS, and that it may have been used against Indian troops in border disputes. Other reports allege that since 2018, Chinese destroyers have had operational DE capabilities, likely aimed at enhancing China’s asymmetric ability to counter U.S. superiority in space.

Russia began researching DE technology like the U.S. in the 1960s. Despite this early investment, many of Russia’s DE projects did not materialize into deployable weapons, and others were paused after the fall of the Soviet Union. Despite these setbacks, early developments provided foundational knowledge for Russia to field several advanced DE systems, including those using HPM technology.

Rumors of early HPM weapons began with the infamous “Moscow Signal,” a suspected microwave weapon targeting U.S. embassy personnel in Russia from the 1950s to 1970s. Some reports indicate Russia will attempt to arm sixth-generation combat drones with microwave weapons. While the deployment of some Russian DE weapons has been confirmed, some may simply be propaganda. Although Russian space initiatives receive only a fraction of the funding granted to U.S. and Chinese programs, a recent Defense Intelligence Agency report indicates that by the mid-to-late 2020s, Russia may field DE weapons capable of damaging satellites.


While electronic warfare (EW) can degrade a target’s operating ability, HPM weapons can degrade, damage, and destroy a target. HPM has demonstrated scalable militarily relevant effects, and when used in operations that benefit from the convergence of effects, cyber, EW, HPM, and traditional kinetic weaponry, the provides flexibility and scalability in the application of power across all phases of conflict. If the Epirus Leonidas system meets the company’s high expectations, it would be a significant milestone in how and where HPM DE weapons can be deployed.  n