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ties. The International Energy Agency has noted that as cities like Moscow, Shanghai, Tokyo and Mexico City attain populations of 20 or even 30 million, they are experiencing a dramatic increase in vehicle usage. Today, there are already more than one billion vehicles in the world. In 2025, there will be 1.5 billion vehicles, including 400 million in China alone, where they will be concentrated in metropolitan areas. In such a context, automated driving will no longer be merely a question of road safety and convenience. Instead, it will offer the only way to keep traffic flowing in cities, where the average speed is already less than 20 km/h due to extreme road usage. Radar technology for automotive applications Radar technology for use in cars differs in several ways from the military applications for which radar was originally developed. Firstly, the automotive industry is subject to enormous cost pressures, so components must be much more economical. In addition, due to the very limited space for radar sensors behind plastic bumpers, the sensors must be extremely compact. Compared with camera and ultrasonic applications, radar has a major advantage in that no visual contact is required between the radar sensor and the object to be detected. This saves costs in the production of bumpers and can also be exploited in the vehicle design. However, it is still a challenge to compensate for the attenuation of the transmit and receive signals as they pass through the different layers of material in the bumper as well as the (metallic) paint. Such compensation Fig. 1: The components of an LFMCW radar signal. is implemented with post-processing in the radar sensor. For automotive applications, vehicle manufacturers can currently make use of four frequency bands at 24 GHz and 77 GHz with different bandwidths. While the 24 GHz ISM band has a maximum bandwidth of 250 MHz, the 24 GHz ultra-wideband (UWB) already offers up to 5 GHz; however, this is allowed only until the end of 2022 due to international regulations. The band that will be available past this date with up to 4 GHz bandwidth lies between the frequencies of 77 GHz and 81 GHz. It is already used for forward-looking applications. Since the signal bandwidth determines the range resolution, it is very important in radar applications. Accordingly, the other allocated frequencies of 122 GHz and 244 GHz for this application with a bandwidth of only 1 GHz will see little use in the automotive industry and are restricted to research projects until further notice. www.electronics-eetimes.com Electronic Engineering Times Europe October 2014 37


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