An automotive radar is used to locate objects, such as vehicles and pedestrians, in the vicinity of the car. A radar consists of a receiver and a transmitter. The transmitter sends out radio waves that hit an object and bounce back to the receiver. By controlling the direction in which radio waves are sent and received it is possible to detect objects' distance, speed and direction. This requires steerable antennas that can be automatically directed or receive signals simultaneously from several different directions.
Automotive radars can be categorized into three types: long range radars, medium range radars and short range radars. Long range radars are used for measuring the distance to and speed of other vehicles. Medium range radars are used for detecting objects within a wider field of view e.g. for cross traffic alert systems. Short range radars are used for sensing in the vicinity of the car, e.g. for parking aid or obstacle detection. Depending on the application, radar requirements differ. Short range applications require a steerable antenna with a large scanning angle, creating a wide field of view. Long range applications on the other hand, require more directive antennas that provide a higher resolution within a more limited scanning range.
Two different frequency bands are mainly used for automotive radars: the 24 GHz band and the 77 GHz band. The 77 GHz band offers higher performance, but it is also more challenging to implement since for example losses are much higher at these frequencies. The 24 GHz radars are easier to develop but are larger in size, making it difficult to integrate them in a vehicle. Radars operating at 24 GHz require around three times larger antennas than radars operating at 77 GHz, to achieve the same performance. A 77 GHz radar would thus be much smaller resulting in easier integration and lower cost.
The most important aspect for moving to higher frequencies is that it enables radars with a better resolution. One of today’s major challenges is therefore to develop steerable antennas for 77 GHz radars with high enough performance at a reasonable cost.
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