Before we go into this subject more deeply, it would be advisable to go back to the previous page and to watch the first video. Now, radar sends out waves, similar to those of radio waves. For this, the very long-wave frequency band of 76 to 77 GHz is reserved. Because radar-sensors depend basically on reflections, a receiver is also always necessary. Although these radio-waves are only reflected from dielectric, thus not from conductive mediums, they also reflect from metallic surfaces.
|Wave-length 4 millimetres|
An analysis of the time it takes to send out, reflect and return, is sufficient to recognize stationary mediums. The speed of the movement and perhaps also its direction, can only be determined by comparing the transmitted and received frequencies. It becomes interesting, when the frequencies are not evenly sent out.
One can see them quite often, the same as the rather expensive rotating radar-aerials on the autonomous, driverless Google-car. They enable reflexions which are sent out in various directions, to be picked up and determined, in this case, also objects on the right- and left hand sides. To be able to do this, in addition, the signal-strength is also evaluated.
|Reflexion with a Doppler-Effect|
In a moving car, the frequency to the front is higher than to the rear.
Actually, we don't to want conclude with just the reflexion frequency as in a radar-trap to determine the speed of a car, but the ability of the radar-sensors to intelligently regulate the distance between two cars. What would happen, as it often does, when the cruise-control is engaged and the car is slowly getting closer and closer to the one in front?
In motor cars, radar is used for the greater distances. The respective sensors can pick up a vehicle ahead at a distance of 100 to 150 meters. This allows enough space and time to react, even at higher speeds. As a matter of interest, the device, which is frequently built into the radiator grille, contains quite a good bit of software.
All this is hardly possible without networking. After all, perhaps another device is checking that the vehicle remains in its lane. The fact is, a movable object is not as easy to determine as a vehicle moving directly in front of you. You only have to think about very tight bends which occur e.g., in motorway road-works. 08/14
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