Modern warfare has witnessed the rapid proliferation of small unmanned aerial vehicles (UAVs) and their swarms, posing an unprecedented challenge to conventional air defense systems. Among various countermeasures, high-power microwave (HPM) technology has emerged as a promising approach due to its ability to disrupt or even permanently damage the electronic systems of hostile drones. In this study, we focus on a specific class of small fixed-wing drones, which are widely used in both civilian and military applications because of their endurance, range, and payload capacity. Understanding the interaction mechanism between HPM electromagnetic fields and the internal electronics of such drones is crucial for developing effective protection and vulnerability assessments.
The objective of this work is to systematically investigate the susceptibility of a typical small fixed-wing drone to S-band HPM radiation. We adopt a combined simulation and experimental methodology, covering system-level, subsystem-level, and component-level analyses. The drone under test is a commercial fixed-wing model constructed primarily from polystyrene, with a small brushless motor for propulsion, a receiver module for command and control, servo motors for flight surface actuation, and an onboard battery. The HPM source operates at a center frequency of 3 GHz with a pulse width in the microsecond range, producing a narrowband waveform that can efficiently couple into electronic circuits through intentional and unintentional apertures.
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Figure 1 shows the typical appearance of a fixed-wing drone similar to the one investigated in this work. The structure includes a fuselage, wings, tail surfaces, and a propeller driven by the motor. The internal layout of critical components is crucial for determining coupling paths.
1. High-Power Microwave Electromagnetic Environment
According to IEC 61000-2-13, high-power electromagnetic environments (HPEM) are classified into several categories, including nuclear electromagnetic pulse (NEMP), ultra-wideband (UWB), mesoband, and narrowband HPM. The narrowband HPM considered here is generated by a source with a peak power of tens of megawatts and is radiated through a directive antenna. In the far-field region, the electric field strength can be estimated using the radar equation:
\[P \cdot G = \frac{4\pi R^2 E^2}{\eta}\]
Rearranging yields the field intensity as a function of distance:
\[E = \frac{\sqrt{30 P G}}{R}\]
where \(P\) is the output power, \(G\) is the antenna gain, \(R\) is the range, and \(\eta\) is the intrinsic impedance of free space (≈ 377 Ω). The typical HPM pulse is modulated by a sinusoidal carrier, and its voltage waveform can be expressed as:
\[E(t) =
\begin{cases}
E_0 \sin(2\pi f_0 t) \, u(t – T), & 0 < t < T (N+1) \\
0, & T(N+1) < t
\end{cases}\]
where \(E_0\) is the peak electric field, \(f_0\) is the carrier frequency (3 GHz in our tests), \(T\) is the pulse period, and \(N\) is the number of cycles within one pulse. For computational efficiency in simulations, we set the pulse width to approximately 3 ns while maintaining the same carrier frequency, scaling the normalized waveform accordingly. The normalized time-domain waveform is depicted in Figure 2 (not shown here, but the mathematical form is given above).
2. Electromagnetic Modeling and Simulation of the Fixed-Wing Drone
To characterize the back-door coupling of HPM into sensitive electronics, we constructed a full three-dimensional electromagnetic model of the drone using a finite-difference time-domain (FDTD) solver. The model includes the fuselage (polystyrene with relative permittivity εr = 2.55, loss tangent δ = 7 × 10−4, and μr = 1), the brushless motor (iron and copper), the receiver circuit board, the battery, servo motors, and the interconnecting cables. The key internal components are positioned as illustrated conceptually in Figure 3 (schematically).
2.1 Body-Level Irradiation Simulation
We first irradiated the entire drone body with a plane wave at a power density of 10 W/cm², S-band frequency, vertical polarization. The simulation captured the electric field distribution across the fuselage and inside the structure. The maximum field enhancement occurred at the wing tips, reaching 24 kV/m. Table 1 summarizes the peak induced electric fields at the locations of critical components.
| Component | Location | Peak E-field (kV/m) | Duration (ns) |
|---|---|---|---|
| DC Power Supply | A | 13.9 | 2.3–6.0 |
| Receiver | B | 7.9 | 3.3–7.6 |
| Wing Servo | C | 6.3 | 3.8–6.5 |
| Brushless Motor | D | 9.6 | 7.0–10.0 |
The induced fields exhibit a damped oscillatory behavior with a frequency closely matching the incident wave. The highest field (13.9 kV/m) occurs at the DC power supply, likely due to the presence of long power wires acting as efficient receiving antennas. The receiver module experiences 7.9 kV/m, which is significant for low-voltage electronics.
2.2 Cable Network Irradiation Simulation
The internal wiring harness of the fixed-wing drone includes servo control lines, battery power cables, and motor phase wires. We modeled the cable bundle as a transmission line network with lumped terminations, as shown schematically in Figure 4 (conceptual). The incident wave was vertically polarized at 10 W/cm². Four probe ports (P1–P4) were defined at the terminal ends of critical cables: DC battery line, brushless motor control line, fuselage servo line, and wing servo line.
Figure 5 (not shown) plots the induced voltages at each port. The wing servo control line exhibited the highest peak induced voltage of 1.9 V, while other ports had peaks near 1.0 V. The relatively low coupling is because the horizontally oriented cables are partially mismatched with the vertical polarization. However, field enhancement due to the fuselage geometry can increase actual levels, which we later validate experimentally.
2.3 Receiver Circuit Board Irradiation Simulation
The receiver board is the most sensitive unit in the drone. We built a detailed model of the printed circuit board (PCB) including the microcontroller, communication transceiver chip, and pin headers. Under a plane wave of 10 W/cm², the induced electric field on the PCB surface reached 257 kV/m in some regions. Voltage monitors placed at three critical nodes recorded the following:
| Port | Description | Peak Voltage (V) | Duration (ns) |
|---|---|---|---|
| N1 | Board pin header | 4.5 | ~3 |
| N2 | Communication chip pin | 1.8 | ~2.5 |
| N3 | Control chip pin to ground | 2.1 | ~3 |
The pin header voltage of 4.5 V is well above typical logic thresholds (e.g., 0.8 V for low, 2.0 V for high in TTL), indicating a high probability of upset. The induced waveforms oscillate at the carrier frequency and persist for the pulse duration. We further simulated the dependency of induced voltages on incident power density, as shown in Table 3. A linear relationship was observed, which is expected for a linear coupling regime below material breakdown.
| Power Density (W/cm²) | Pin Header (V) | Communication Chip Pin (V) | Control Chip Pin (V) |
|---|---|---|---|
| 1 | 0.45 | 0.18 | 0.21 |
| 5 | 2.25 | 0.90 | 1.05 |
| 10 | 4.50 | 1.80 | 2.10 |
| 20 | 9.00 | 3.60 | 4.20 |
The data suggests that when the power density exceeds approximately 5 W/cm², the induced voltage on chip pins surpasses 1 V, which is sufficient to cause logic state transitions or latch-up effects. At 10 W/cm², the risk of upset is high; above 20 W/cm², permanent damage becomes likely, as we later confirm experimentally.
3. High-Power Microwave Effect Experiments on Fixed-Wing Drone
To validate the simulation predictions, we conducted a series of HPM irradiation tests on the same fixed-wing drone. The experimental setup is illustrated in Figure 6 (conceptual). The HPM source operated at S-band, vertical polarization, with adjustable pulse width and repetition rate. A calibrated receiving antenna and power meter were used to measure the incident power density at the drone position. The drone was placed horizontally, facing the antenna, and its response was monitored via telemetry link and on-board indicator LEDs.
3.1 Full-System Irradiation
We varied the drone’s distance from the antenna to achieve different power densities. The relationship between distance and power density was measured and is summarized in Table 4.
| Distance (m) | Power Density (W/cm²) |
|---|---|
| 2.0 | 10.5 |
| 2.5 | 7.9 |
| 3.0 | 5.5 |
| 4.0 | 3.2 |
At 5.5 W/cm², the drone exhibited intermittent communication loss with the controller. At 7.9 W/cm², a stable upset effect was observed: the receiver lost contact with the remote controller, the motor stopped, and all servo actuators became unresponsive. After several exposures at 10.5 W/cm², the drone suffered permanent failure—the receiver could not recover even after the HPM was turned off. We therefore selected 7.9 W/cm² as the nominal test level for subsequent subsystem experiments.
3.2 Subsystem-Level Experiments
We performed controlled experiments by disconnecting certain subsystems to isolate the dominant coupling path. First, we removed all servo control cables, leaving only the receiver connected to the battery and the electronic speed controller (ESC) for the motor. Under 7.9 W/cm², the receiver still lost communication and the motor stopped. This indicated that servo cables were not the primary cause.
Second, we disconnected the motor and ESC, keeping only the receiver connected to the battery and one wing servo. The same upset occurred: the receiver dropped the link and the servo became motionless. Hence, the motor and its wires were also not the main path.
3.3 Receiver-Only Irradiation
Finally, we extracted the receiver module alone, powered it with a battery placed inside an EMI-shielded box, and exposed it to the same HPM environment. The receiver’s output pins were monitored with an oscilloscope. Before irradiation, the communication pin (Pin 1) and control pin (Pin 2) were functioning normally, producing proper pulse-width modulation signals. After a 3-second exposure at 7.9 W/cm², the output signals changed dramatically:
| Pin | Before HPM | After HPM |
|---|---|---|
| Communication Pin 1 | PWM signal (active) | DC constant high |
| Communication Pin 2 | PWM signal (active) | No output (flat line) |
| Control Pin 1 | PWM signal (active) | No output (flat line) |
These results confirm that the receiver alone is highly susceptible: the induced voltage from the HPM field disrupts the internal microcontroller, latching its outputs. The upset is non-destructive within a few pulses but can become permanent after repeated or higher-level exposure. The experimental upset threshold (around 7.9 W/cm²) agrees well with the simulation-predicted threshold of ~5 W/cm², considering modeling uncertainties and actual field enhancement.
4. Conclusion
Through a combined simulation and experimental approach, we have identified the vulnerability mechanisms of a typical small fixed-wing drone to S-band high-power microwave radiation. The key findings are:
- The receiver module is the most sensitive component, with pin header induced voltages exceeding 4.5 V at 10 W/cm² in simulation, and confirmed upset at 7.9 W/cm² in experiment.
- Cable coupling from servo and motor wires contributes less significantly to system upset; the primary coupling path is directly into the receiver circuit board through structural apertures and imperfect shielding.
- The incident power density threshold for stable upset is approximately 5–8 W/cm², while permanent damage occurs above 10 W/cm².
- The linear relationship between induced voltage and power density observed in simulations was validated by the experimental trend.
These results provide a quantitative basis for developing hardening strategies for fixed-wing drones against HPM threats, such as adding shielding to the receiver, using ferrite chokes on cables, and implementing software-based error detection. Future work will explore multi-pulse effects and the impact of polarization and incidence angle variations.