The Radar Sensor

Radar History

Radars have been in use since 1930s when they were primarily used by the military to detect aircraft, but since then the radar technology has come a long way and today they are increasingly being used as automotive radar sensor for advanced driver assistance systems (ADAS). The image below shows how radar sensors are used along with a full suite of other sensors in an autonomous vehicle:

The advancements in the RF technologies and Digital Signal processing have made it possible to design efficient radars at low cost and in smaller sizes. The radar’s capability to determine the targets at long range with accurate velocity and spatial information make it an important sensor for self driving applications. Additionally, its capability to sense objects in dark and poor weather (rain, fog) conditions also help it cover the domains where LIDAR or camera may fail.

Radar Operation

Radar works using the transmission and detection of electromagnetic waves as seen in the following image:

The electromagnetic waves are reflected if they meet an obstacle. If these reflected waves are received again at the place of their origin, then that means an obstacle is in the propagation direction.

The frequency of electromagnetic energy used for radar is unaffected by darkness and also penetrates fog and clouds. This permits radar systems to determine the position of road targets that are invisible to the naked eye because of distance, darkness, or weather.

Modern radar can extract widely more information from a target's echo signal than its range.

Radar Construction

The automotive radars are small size sensors that can easily fit beneath the front grill or the bumper. As seen in the image above a radar module comprises of different parts.

• Radar Dome or Radome : A radome is a structural, weatherproof enclosure that protects a radar antenna. The radome is constructed of material that minimally attenuates the electromagnetic signal transmitted or received by the antenna, effectively transparent to radio waves.

• Radar Printed Circuit Board : This is analog hardware that includes the radar transceiver and antenna needed for radio wave generation.

• Printed Circuit Board and Processing : This includes the Digital Signal Processing (DSP) unit.

Radar vs Lidar

One can find many of articles comparing the LIDAR and RADAR, but in practice, these sensors are complementary to each other.

LIDAR can generate high resolution imaging based on reflection of the laser light off from the targets. But LIDARs fail in bad weather conditions as the very small wavelength doesn’t allow to work well in fog or rain. Additionally, LIDAR is an expensive sensor with costs varying from $35,000 to $100,000 as of 2019. Lidar is the preferred technology at Waymo.

Radar lacks the capability to generate a high resolution image, but it has highly accurate velocity estimation based on the doppler phenomenon, which we will cover in more detail later in this course.
Also, radar wavelength allows it to sense the targets in bad weather conditions as well. Most important is the low manufacturing cost for a Radar. A radar unit can cost as low as a few hundred dollars, allowing a car manufacturer to deploy multiple Radar sensors for 360 degree perception. Tesla relies on Radar as its primary sensor and doesn’t include LIDAR in its sensor fusion system.

Read how Delphi used MATLAB and code generation to implement a radar safety system

Radar Quiz