CW vs. FMCW Radar: Detecting Drone Propeller Micro-Motions | Airsight

While the industry often focuses on detecting the "body" of a drone, true security lies in the rotors. The micro-motions of multi-rotor propeller blades produce a unique micro-Doppler signature that acts as an acoustic-like fingerprint, allowing for high-fidelity classification between a bird and a quadcopter.

However, not all radar is created equal when it comes to capturing these high-speed flashes. The debate between Continuous Wave (CW) and Frequency-Modulated Continuous Wave (FMCW) radar is central to building a professional drone detection solution in 2026.

The Physics of CW Radar: The Velocity Specialist

Continuous Wave (CW) radar is the simplest form of radar technology. It transmits a steady, unmodulated radio frequency signal and measures the Doppler shift of the return signal.

• The Advantage: Because CW radar transmits continuously without breaks, it has an effectively infinite "dwell time" on a target. This allows it to capture incredibly rich, high-resolution micro-Doppler signatures of fast-spinning blades that pulsed radars might miss.
• The Fatal Flaw: Unmodulated CW radar has no way of measuring time-of-flight. It can tell you how fast a drone's blades are spinning, but it cannot tell you how far away the drone is. For a security team, a drone moving at 40 mph at a distance of 10 meters looks identical to one at 100 meters.

The Rise of FMCW Radar: The All-In-One Solution

Frequency-Modulated Continuous Wave (FMCW) radar solves the range problem by "modulating" the signal - usually in a "chirp" pattern where the frequency increases or decreases linearly over time.

1. Simultaneous Range and Velocity

By comparing the frequency of the received echo to the frequency being transmitted at that exact micro-second, the system can calculate both the Doppler shift (velocity) and the time delay (range). This is the standard for modern drone detection radar.

2. Superior Clutter Rejection

FMCW radar creates a Range-Doppler Map. This allows the system to isolate the micro-motions of propeller blades within a specific "range bin."

• The Benefit: If a drone is hovering near a tree or a wall, CW radar would be overwhelmed by the "clutter" of the static object. FMCW radar simply ignores the static reflections in that range bin and focuses only on the high-frequency micro-motions of the drone rotors.

3. High-Frequency Resolution

In 2026, FMCW systems operating in the mmWave bands (77–81 GHz) provide the extreme bandwidth (up to 4 GHz) necessary to achieve sub-centimeter range resolution. This allows the radar to not only see the drone but to distinguish between the vibrations of the chassis and the rotation of the individual blades.

Why FMCW Wins in 2026

While CW radar remains a useful tool in laboratory settings for studying isolated blade physics, it is insufficient for real-world airspace security.

FMCW radar is the superior technique for three reasons:

• Tactical Awareness: Knowing the range and altitude is critical for a coordinated law enforcement response.
• Autonomous Detection: It can track non-communicating drones that are hovering silently (minimal Doppler) but have active rotors (rich micro-Doppler).
• Multi-Target Tracking: It can distinguish between multiple drones in the same vicinity by separating them into different range and velocity bins.

The Airsight Advantage

Airsight's AirGuard platform is built to leverage the strengths of high-resolution FMCW radar integrated with RF and optical sensors. By utilizing mmWave FMCW technology, we ensure that your security team isn't just seeing "movement," but is receiving precise, classified intelligence on the range, speed, and intent of every aircraft in your vicinity.

Airspace Security as a Data Integrity Challenge

In 2026, the primary challenge of counter-UAS operations is no longer just detecting presence, but establishing intent and identity in cluttered environments. As the industry moves toward autonomous, non-cooperative threats, the reliance on simple velocity data is a tactical vulnerability.

Modern airspace resilience requires the fusion of high-frequency FMCW radar, RF intelligence, and AI-driven classification. By isolating micro-motions within precise range bins, security teams can transform raw sensor data into forensic-grade intelligence. Airsight provides the technical architecture necessary to navigate this transition, ensuring that critical infrastructure is protected by high-fidelity tracking rather than just motion alerts.