Radar 101: Why are automotive radar systems shifting to 77GHz?
Autonomous cars are here with level 3 autonomy being tested on the roads, with many tech giants investing heavily on the technology. Radar technology even though existed from nearly a century ago it is finding its application in consumer/ passenger vehicles in this century. These advances have fueled increase in radar application. Most manufacturers and OEMs are concentrating towards advance driver assists system cause we are still a long way from fully autonomous cars. Even with full autonomy the cars still need to depend on radar. Some of the manufacturers are also looking at sensor fusion with imaging sensors and radar for better accuracy and performance. To handle the processing load most board manufactures are also working on better EVMs. However, few regulations put forth by governing body has mad the industry to switch from 24GHz to 77-81GHz. Although in the past the 24GHz bandwidth was being employed, nowadays the global community has converged towards 77-81 GHz bandwidth due to their various advantages specific to the field of automotive radar. Let us understand what these regulations actually suggest.
As the demands of the automotive industry had been increasing, the EU decided to regulate and standardize the usage of short range radar for automotive purposes. The EU stated the following regarding the power and the frequency spectrum of short range radar applications:
- The ‘79 GHz range radio spectrum band’ shall mean the frequency range between 77 and 81 gigahertz
- The maximum mean power density shall be of – 3 dBm/MHz Effective Isotropic Radiated Power (EIRP.) associated with a peak limit of 55 dBm EIRP.
- The maximum mean power density outside a vehicle resulting from the operation of one short-range radar shall not exceed – 9 dBm/MHz EIRP
To improve collision warning and driver safety in cars FCC amended radar application norms. This also talks about radar application at airports to improve overall safety of drivers and airport personnel.
- Elimination of in motion and not-in-motion tags for vehicular radar
- Uniform emission limits for forwards, side and rear mounted radar
- Increased average power density limit to 88 µW/cm² at 3 meters (average EIRP of 50 dBm) and decreased peak power density limit to279 µW/cm² at 3 meters (peak EIRP of 55 dBm) for vehicular radar systems regardless of the direction of illumination.
24GHz in automotive radar systems
The 24 GHz band consists of a narrow band lying in the range of 24GHz to 24.50GHz. It also consists of a ultra-wide band of 5GHz. The ultra-wide comes in handy for various ADAS application such as forward collision warning and blind spot detection. However due to modifications in the spectrum regulations by various international bodies such as the FCC, the ultra-wide band will soon be obsolete.
77GHz in automotive radar systems
The 77 GHz band allows for a bandwidth sweep of 4GHz resulting a max frequency of 81 GHz. This band is extremely attractive in short range radar applications in the automotive industry. Radar technology helps us determine three major parameters with relative ease. The three parameters being range, relative velocity and direction of arrival.
- Range and velocity having a wider bandwidth of 4 GHz is extremely beneficial. It increases range resolution and velocity resolution and hence allows us to distinguish objects that are closely spaced, making it very advantageous in use-cases such as automated parking for instance.
- Another reason why 77 GHz is very beneficial is because it reduces the size and the form factor of the device thereby making it very attractive for automotive companies, allowing them to mount these sensors in tricky positions.