Antennas in automobile radar

Abstract

Automobile radars are under investigation since the 1960s. The first operational systems are on the market since 1992 for buses and trucks and 1999 for passenger cars, both in the frequency range around 24 as well as 76.5 GHz; a new frequency band for medium- and short-range sensors from 77 to 81 GHz has been allocated recently in Europe. Requirements for the sensor antennas are high gain and low loss combined with small size and depth for vehicle integration. Great challenges are due to the millimeter-wave frequency range, and a great cost pressure for this commercial application determines design and fabrication. Consequently, planar antennas are dominating in the lower frequency range, while lens and reflector antennas had been the first choice at 76.5 GHz, partly in folded configurations. With increasing requirements toward a much more detailed view on the scenery in front or around the vehicle, multi-beam antennas or scanning antennas have been designed. For actual systems, digital beamforming with a number of integrated antennas is in use or under development, and also MIMO concepts will be exploited. With such development, antennas for automotive radar no longer can be considered as stand-alone devices, but will be part of an "imaging" system including multiple transmit/receive units and digital signal processing. General antenna concepts, partly including system aspects, as well as several realized antenna and sensor configurations will be described in detail in this chapter.