During the ongoing war in Ukraine, both sides have exploited the use of cheap, commercially available drone technology for use against their adversary. Drones and Unmanned Aerial Vehicles (UAVs) represent a significant and ever-emerging threat on both the battlefield and homeland. Recently, the Air Force recognized and addressed this threat by creating the Air Force Counter-Small Unmanned Aircraft Systems effort to address the specific threat drones and small unmanned aircraft systems (sUAS) pose to military installations.
The US Air Force and Navy have both created mature drone-defense systems in partnership with US contractors, such as the Air Force’s Tactical High-power Operational Responder (THOR) and multiple systems in the works with the Navy’s NSWCDD HPM Weapon Systems Division.
Figure 1 AFRL’s THOR counter-UAS system. Photo Credit: Adrian Lucero/US Air Force
While the majority of the systems are High-Power Microwave (HPM) systems that utilize a highly-directed beam of microwave energy for coupling into and disabling/defeating drones, the need for addressing a “swarm” of drones still exists. Applied Physical Electronics L.C. (APELC) has recently developed several high-powered wideband systems that create an extremely high electric field (hundreds of kV/m at 1m) with very wide beam-widths, that have the potential for addressing the swarm concern.
OVERVIEW OF HIGH-POWER ELECTROMAGNETIC SYSTEMS FOR DIRECTED ENERGY
Throughout the history of directed energy technology development, the Department of Defense and associated contractors have focused on a number of different technologies for generating the high electric fields and/or peak power required to disrupt, disable, or even destroy electronic systems. A brief comparison of these technologies is presented below.
Ultra-Wideband (UWB) was at one point a major focus of many development efforts, as extremely high field strengths (~60kV/m at 85m) had been reported by systems such as the Air Force’s JOLT system. As showing in Figure 2, these systems are capable of producing very high field strengths, with extremely short, fast-rising (10’s to 100’s of ps) pulses. While the high electric fields produced by these systems had the potential to disrupt electronics, interest in these systems eventually waned due to the very low energy actually radiated by the system.
Figure 2 The Air Force’s JOLT UWB system
Figure 3 Example of an UWB waveform and associated spectrum
High-Power Microwave (HPM) systems represent the dominant directed energy technology used today for drone defense. By using pulse compression techniques, extremely high peak-power microwave fields are generated in bursts of typically < 1 microsecond (see example waveform and spectra in Figure 4). With a narrow bandwidth, these systems are able to generate narrow beam-widths and deliver high peak powers on target. The advantage of these systems lies in their ability to concentrate energy in a narrow portion of the spectrum that is tuned for maximum effect on a given target. The down-sides exist in the large ancillary systems required to operate and source the vacuum diode loads, as well as the narrow beam-width not necessarily being ideal for illumination of large swarm attacks.
Figure 4 Example of HPM waveform and spectrum
Wideband High-power RF
Whereas HPM systems have a very narrow bandwidth (percent bandwidth <1%) as shown in Figure 4, Wideband high-power RF systems have fewer cycles of energy and therefore spread their energy across a wider portion of the spectrum, as shown in Figure 5. While this does distribute the total amount of energy delivered onto the target across a broader spectrum, it does make for a cost-effective system with a very wide beam width and high field strength. Moreover, wideband systems do not require the cumbersome support equipment involved with many HPM systems, and can therefore be made more compact and less-expensive.
Figure 5 Example of Wideband waveform and spectrum
The design of such as system is relatively straightforward, with a simple RLC resonator circuit used to generate the frequency content (Figure 6). In the case of APELC’s wideband systems, the capacitance of the resonator circuit is pulse charged by a Marx generator at hundreds of kilovolts, which is in turn discharged into a wideband antenna load.
Figure 6 simple RLC oscillator circuit
The resulting waveform is a damped sinusoid that is radiated through the antenna and directed with a reflector. The beam-width for this system is therefore extremely wide (>40 degrees) and capable of illuminating a swarm of incoming drones/UAVs at a significant distance. An example of such a system is shown in Figure 7.
Figure 7 Example of an APELC counter-drone/UAV system
APELC presently manufactures a number of wideband systems for electronics effects testing that represent the basis of this technology. A few examples are provided in the figures below:
Figure 8 APELC suitcase high-power RF system
Figure 9 APELC “Footlocker” high-power RF system
Figure 10 APELC RFXC-400 drone-deployable high-power RF system
More information on these systems can be found here: https://apelc.com/high-power-rf/