Before You Can Stop a Drone, You Have to See It

Counter-drone systems combine radar, RF detection, and optical sensors to find and identify small uncrewed aircraft. Before a response can be selected, the system needs a reliable track.

The end of a counter-drone engagement is easy to picture: a missile launches, a gun fires, a jammer disrupts a control link, or a laser tracks the target. But each response depends on the system first detecting an object and determining what it is. That is rarely straightforward with small uncrewed aircraft, which can be physically small, fly low, and blend into clutter from buildings, vehicles, birds, and other objects.

Some drones use radio links that can be detected; others emit little useful radio-frequency (RF) signal. Modern counter-uncrewed aircraft systems (counter-UAS) combine different sensor types rather than relying on a single technology.

Detection comes first

The US Department of Defense describes counter-UAS detection as a layered process, with each sensor type contributing information that others may not provide. Radar detects objects and tracks their movement. RF sensors monitor signals between an aircraft and its controller. Acoustic sensors can detect motor and propeller noise. Electro-optical and infrared (EO/IR) cameras provide visual information that helps operators identify a detected object and maintain observation.

Detection and identification are separate tasks. A radar return can indicate that an object is moving through a section of sky, but it cannot necessarily establish whether that object is a hostile drone, a friendly aircraft, or a bird. As a system approaches an engagement decision, reliable identification becomes increasingly important.

Why one sensor is rarely enough

The US Army demonstrated this layered approach at Balikatan 2025 in the Philippines, operating its Fixed Site Low, Slow, Small UAS Integrated Defeat System (FS-LIDS) alongside a high-power microwave weapon. FS-LIDS handled sensing and tracking, while an electro-optical/infrared camera let operators identify the target before engagement. The Army’s Mobile-LIDS (M-LIDS) system follows a similar principle, combining radar, direction-finding sensors, and an EO/IR camera with command-and-control and electronic-warfare equipment.

Each sensing method has limitations. RF detection depends on available signals, cameras need line of sight, and radar performance varies with target size and the surrounding environment. Combining sensors can help cover these gaps. The challenge is to bring their inputs together quickly enough to support a reliable decision.

The optics inside the sensor matter too

EO/IR cameras, LiDAR, and laser-tracking systems are optical systems and sensing technologies. Light must pass through lenses, mirrors, and other components before reaching a detector, where it is converted into information for processing. Active systems may also need to scan a beam across a wide field of view and then track a target, bringing beam-steering optics into the design. A scanning mirror has a demanding job: to direct the beam quickly and accurately, repeatedly, across the required range of angles. Martynas Adomaitis, Market Development Manager at OPTOMAN, says these components can limit the performance of the wider sensor system:

“People naturally focus on the detector and the software because that is where the information is produced. But the optical system still has to deliver the right signal first. In a fast beam-steering system, changes in reflectivity, scan angle, or thermal behavior can affect what reaches the detector before the processing even begins.”

OPTOMAN’s hybrid scanning mirrors are designed for applications including LiDAR, advanced sensing, and directed energy. They combine dielectric and metallic reflector layers to provide high reflectivity at the main laser wavelength while maintaining broadband performance across a wider range of angles of incidence. For military sensors, optical performance needs to remain consistent as the system scans and operates for extended periods.

Wide scan angles add complexity

A fixed mirror can be optimized for light arriving at a particular angle. A scanning mirror operates across a range of angles of incidence, and its coating performance can change as it moves.

This creates a design trade-off. Dielectric coatings can provide very high reflectivity at selected wavelengths, but maintaining that performance across a broad range of angles and wavelengths is more challenging. Metallic reflectors generally offer broader angular and spectral response but have different optical losses.

Reflectance of hybrid scanning mirror coating at 35° and 55° AOI.

When a tracking system moves from scanning a wide area to following a specific object, changes in reflectivity or other optical characteristics across the scan range can affect the signal reaching the detector. The coating therefore needs to be designed around the system’s wavelength range, scan angles, and performance requirements.

Heat can affect optical performance

Absorption in a coating converts some of the incident optical energy into heat. At higher optical powers, the resulting thermal load can affect an optic surface or optical properties. Small changes can shift the beam or affect where it lands.

A beam-steering component may need to maintain reflectivity across a wide scan angle, withstand repeated mechanical movement, and preserve its optical figure under thermal load. Meeting these requirements together is a significant part of the design challenge.

The environment still matters

Even a well-designed sensor depends on its operating conditions. Line of sight, weather, smoke, dust, darkness, and background clutter affect EO/IR performance. This is another reason to combine sensing technologies: radar or RF may continue to provide useful information when optical visibility is poor, while optical sensors can help identify a target when RF information is limited.

Sensor fusion is not just a software task. The processing system can only work with the data the hardware collects. No algorithm can recover information that never reached the detector.

The weapon depends on the quality of its track

Counter-drone discussions often focus on the defeat mechanism — lasers, missiles, guns, electronic warfare or high-power microwave systems — because those are the most visible parts of the technology. But an engagement also depends on the sensor chain that detects, identifies, and tracks the target. Radar may provide an initial cue; RF can add context, and EO/IR can help confirm what is in view. Optical tracking may then need to follow a small, moving target while the response system operates.

As counter-UAS systems become more widely deployed, they will need to distinguish relevant targets from clutter while limiting false alarms. The final response may take only seconds, but it depends on reliable information gathered well before that point.