Radiation Detecting and Ranging is a technology that must clearly be counted as part of the sensor technology in the motor vehicle. The best-known example is the distance sensor, but radar technology is basically divided into close-range, medium-range and long-range, at the moment there is still a separate device for each. Radar works with radio waves or electromagnetic waves with a longer wavelength than that of visible light, but smaller than that of lidar, for example.

The entire spectrum of radar waves can be used in different ways. Depending on the frequency band, they can not only penetrate concrete walls, but also clouds and rain. The frequencies 76 and 77 GHz are approved for road traffic. Although a sensor, such a device initially sends wave packets vertically more widely spread than horizontally to the front. Metal is a particularly good reflector, but radar would probably also work if the rear of the vehicle were only made of plastic, for example.

We will come to the evaluation of the signals, which basically move at the speed of light, later. In any case, it is usually already possible in the sensor to first determine the distance from this and, by means of many measurements in quick succession, also the speed. The horizontal angle at which the beams are emitted is dimensioned in such a way that they can detect at least the edges of objects in front and thus also their direction. Emitted is either multiplied or panned.

There is a complete assistance for the driver, which goes far beyond a cruise control function, which is why it is referred to as Adaptive Cruise Control. The situation is relatively simple if the vehicle is recognized from a greater distance. This makes it possible to adapt to its speed by releasing the accelerator pedal. It becomes more critical if such a car cuts in, which then possibly makes a brake intervention necessary. Meanwhile, the following distance can also be changed within limits.

Of course, it has to be continuously adapted to the speed at which you are driving. The assignment of the relevant target vehicle is also not always easy. One only needs to think of curves, which are, however, relatively narrowly delimited on the vast majority of motorways. Together with a lane departure warning system, ACC (Adaptive Cruise Control) already achieves level 2 of autonomous driving. The values of the ESC (Electronic Stability Control) and steering angle sensors, which can be transmitted via the bus system, help to calculate curves.

Radar has been around for a very long time. As the unit for the frequency makes clear, the foundation for the behavior of electromagnetic waves was laid by Heinrich Hertz as early as 1886. He also demonstrated their reflection on metallic objects. With the first radio connection across the English Channel in 1899 and a transatlantic one from 1902, the Italian Guglielmo Marconi succeeded in entering radio technology worldwide, e.g. to enable ships in distress to make an emergency call.

Christian Hülsmeyer made the first distance measurements with this technology in 1904. But radar technology only got the decisive boost from the Second World War and its preparation. The tremendous development stimulus from 1935 to 1945 was triggered by the expected ability of radar systems to detect attacking enemy vehicles from a distance of 100 km, to determine their location and to be able to initiate appropriate countermeasures.

With the initial passive radio measurement technology, for example, a region is protected by setting up transmitting (2) and receiving antennas (3) at greater distances. Strong energy sources (1) emit very short-wave, bundled radiation. This can be made visible on the (then still round) screen (5) of an oscilloscope (4) (picture).

In the simplest case, the received signal is applied to the vertically deflecting plates, while the electron beam is deflected horizontally dependent on time. The time is adjusted to the speed of the possibly reflected waves. In the example above, a reflection has taken place at a distance of approx. 35 km. Using the similiar evaluation from different points, the positions of aircraft/ships can be determined and defense forces can be used in a targeted manner.

The comparison of the received and the transmitted signal leads to a systematic evaluation. Of course, it would be difficult to determine when a signal that always changes in the same way returns, by how many wave troughs or crests the delay would now have occurred. For this reason, the signal is e.g. digitized and stretched by pulse width modulation in such a way that the change is shifted within a single, easily recognizable area.

Presumably it is also because there are devices for different distances. However, one and the same transmitter can of course make changes to the frequency of the possible transmissions, e.g. at the frequency which makes recognition and evaluation possible. The Doppler effect is also helpful for determining the approximation, as it ensures that the frequency of the received waves increases significantly and can therefore be evaluated. The Doppler effect is also helpful for determining the convergence, as it ensures that the frequency of the received waves increases significantly and can therefore be evaluated.

In the development of weapons, radar is almost even more important. For example, there is the stealth bomber, the shape of which and the materials chosen mean that only a few radar beams are reflected. However, the Chinese now claim to be able to locate such aircrafts with 90 percent certainty. On the other hand, there is the German company Hensoldt, which announces that it can locate an aircraft without emitting magnetic waves (passive radar technology) by evaluating all possible waves surrounding an aircraft.