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Automotive Radar Systems

Automotive Radar Systems
Radar is an essential element of ADAS systems and is often used in conjunction with other systems including LIDAR, vision sensors and ultrasonics. Combining these technologies via sensor fusion allows each system to work to their strengths and provides resilience and confirmation.

Typically, three types of radar will be found in an ADAS system,: long-range radar (LRR) is capable of detection at distances up to 250 metres, while medium-range radar (MRR) operates in the 1-60 metres range and short-range radar (SRR) covers the 1-30 metres range – useful for applications such as blind-spot detection, lane change assistance, parking aids etc.
Automotive Radar Systems

Radar sensors are generally mounted to all four sides (front, rear, left and right) of a vehicle. The operating frequency used initially was 24GHz although this is now being superseded by 77GHz solutions. The 77GHz system (including major components and antennas) is much smaller and the detection range and resolution is better than the 24GHz alternative.

Two types of radar are commonly used. Pulse-Doppler radar sends out a short pulse with high peak power at regular intervals, known as the pulse repetition interval (PRI). In these systems – often called half-duplex – after the transmitter has sent the pulses it is turned off and the receiver is activated. The receiver is activated and measures the time-of-flight (TOF) by which the distance of the reflecting object can be calculated.

Additionally, if the phase shift between multiple pulses is measured using the Doppler Effect, the relative velocity of the reflecting object can be calculated and, because the ADAS system knows the velocity of the vehicle with the radar sensor mounted, the absolute velocity of the object is easily deduced. Pulse-Doppler systems are best suited to longer-range use due to the slight delay between switching off the transmitter and activating the receiver.

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