Millimeter-Wave Radar

A radar that transmits millimeter-wavelength electromagnetic waves to measure a target’s distance, speed, and bearing.

Millimeter-wave radar operates in roughly the 30–300 GHz band; automotive systems typically use frequencies near 77 GHz. It transmits a frequency-modulated electromagnetic wave and computes a target’s distance, radial velocity (via the Doppler effect), and bearing angle from the reflected signal. Its advantages are that it works through rain, fog, and darkness, and measures velocity directly; its drawbacks are coarse angular resolution and a sparse point cloud, which make it hard to resolve an object’s shape. “4D” millimeter-wave radar additionally measures elevation angle, giving a denser point cloud. In self-driving cars it is fused with cameras and lidar as part of multi-sensor fusion; in robotics it is used mainly for safety guarding and detecting people nearby.

ExampleA car’s forward-facing 77 GHz radar can still measure the distance and relative speed of the vehicle ahead in rain or fog, which is what makes adaptive cruise control work in bad weather.

Also called

mmWave Radar, mmWave, 4D Millimeter-Wave Radar

Related

LiDAR · Multi-Sensor Fusion · Autonomous Driving · Ultrasonic Sensor · Exteroception

Sources

The fundamentals of millimeter wave radar sensors - Texas Instruments