Working Principle of Millimeter Wave Radar

Millimeter wave radar operates by transmitting high-frequency electromagnetic waves (millimeter waves, frequency: 30–300 GHz, wavelength: 1–10 mm). These waves bounce off vehicles, pedestrians and other obstacles, and the radar receives the reflected echoes. It calculates targets’ distance, velocity and azimuth through three core physical theories: Time-of-Flight (TOF) ranging, Doppler Effect speed measurement, and phase-interferometry angle detection.

1. Ranging via Time-of-Flight (TOF)

Electromagnetic waves travel at a fixed speed of light. The radar records the time gap between signal transmission and echo reception. The target distance is calculated with the formula: R=2c×Δt​. The division by 2 accounts for the round trip of the wave. Roadside radar like the matched sensor of Digital Fusion Probe adopts FMCW (Frequency Modulated Continuous Wave) technology, converting frequency offset into flight time to achieve centimeter-level positioning accuracy up to ±0.2 m.

2. Speed Measurement via Doppler Effect

Moving targets shift the frequency of reflected millimeter waves. If a target approaches the radar, the echo frequency rises; if it moves away, the frequency drops. The radar computes real-time speed directly from this frequency difference, delivering ultra-high speed precision (±0.125 km/h for Laper-2000 supporting radar) without being affected by light or weather.

3. Angle Detection via Phase Difference

The radar is equipped with an array of receiving antennas. Reflected waves from one target reach different antennas with tiny phase differences. By comparing these phase offsets, the system calculates the horizontal and vertical angles of the target, distinguishes vehicles in adjacent lanes, and realizes high-precision angular resolution as low as 1°.

Complete Operation Flow of FMCW Millimeter Wave Radar

1. Transmit linear frequency-modulated millimeter wave signals through directional antennas.
2. Waves reflect off road targets such as cars and pedestrians.
3. Multi-channel antennas capture the reflected echo signals simultaneously.
4. Mix transmitted signals and echoes to generate intermediate difference-frequency signals.
5. Process signals via FFT (Fast Fourier Transform) to extract separate distance, speed and angle data.
6. Cluster scattered reflection points into individual targets and continuously track up to 500 objects at once.
7. Output structured data including target coordinates, speed and vehicle type for radar-camera fusion and digital twin traffic platforms.