Automotive Radar Basics

Automotive radars are used to detect the speed and range of objects in the vicinity of the car. An automotive radar consists of a transmitter and a receiver. The transmitter sends out radio waves that hit an object and bounce back to the receiver, determining the objects' distance, speed and direction.

Automotive radar sensors can be classified into two categories: Short-Range Radar (SRR), and Long-Range Radar (LRR).

Short-range radar (SRR): Short-range radars (SRR) use the 24 GHz frequency and are used for short range applications like blind-spot detection, parking aid or obstacle detection and collision avoidance. These radars need a steerable antenna with a large scanning angle, creating a wide field of view. 

The SRRs have been using the 24 GHz ISM band from 24.0 to 24.25 GHz with a bandwidth of 250 MHz, also called as the narrowband (NB). A bandwidth of 5 GHz, from 21.65 to 26.65 GHz - called as Ultra-Wideband (UWB) - is also available for automotive applications. But this UBW band will become obsolete by the year 2022 in both Europe and the U.S due to the Federal Communications Commission (FCC) and the European Telecommunications Standards Institute (ETSI) spectrum regularization. 

24 GHz automotive radar systems are still ideal for tight budget constraints applications.

Long-range radar (LRR): Long-range radars (LRR) using the 77 GHz band (from 76-81GHz) provide better accuracy and better resolution in a smaller package. They are used for measuring the distance to, speed of other vehicles and detecting objects within a wider field of view e.g. for cross traffic alert systems. Long range applications need directive antennas that provide a higher resolution within a more limited scanning range. Long-range radar (LRR) systems provide ranges of 80 m to 200 m or greater.

We have seen most automotive companies and automotive radar chipset manufacturers move to the 77 GHz frequency band. Click here to read about the advantages of 77 GHz automotive radars.

Functioning of an Automotive Radar

An automotive radar chipset has multiple transmit and receive channels. The different transmit channels are used to drive different antennas (near and long range scans for instance). These multiple transmit channels also provides beam steering capabilities. 

Multiple receive channels gives the angular information about the object as there is phase difference between signals received by different receive antennas.