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FMCW radar: the basics

FMCW radar sensor – the basics

Learn about the measuring principle and how FMCW radar distance sensors work.

Radar sensors for distance measurement or collision avoidance are usually based on the frequency modulated continuous wave radar (FMCW). OndoSense relies on the latest FMCW radar technology and innovative FMCW radar algorithms. Learn more about the measurement principle and how FMCW radar distance sensors work!

FMCW-Radar: Frequency-Modulated Continous Wave

The radar with the “chirp” – a continuously modulated radar signal

OndoSense uses a frequency modulated continuous wave radar (FMCW) for distance measurement. The FMCW radar emits a radar frequency that is continuously increased or reduced over a defined frequency band width (bw).

This usually linear frequency modulation is called sweep or chirp. The duration of this recurring modulation is called chirp time (t).

FMCW type: Sawtooth modulation with linear chirp

The radar signal increases linearly from minimum to maximum frequency (up chirp)

In addition to triangular modulation, the sawtooth modulation used here is one of the most common FMCW processes. In the sawtooth method, the radar signal is continuously increased from the minimum to the maximum frequency (up chirp) – e. g. in the ISM band from 122 GHz to 123 GHz.

If the emitted radar signal hits an object, the radar waves are reflected in whole or in part and received by the radar sensor. The received radar signal has a different frequency than the emitted signal. From the frequency shift (Δ f) of the two signals, the radar sensor can determine the exact distance to the object.

The distance (d) to the target object is calculated from the chirp time (t), the frequency difference (Δ f), the total frequency band width of the chirps, and the (approximate) speed of light (c) at which the radar waves move through the space.

The sawtooth process is also suitable for the so-called fast chirping: Very short chirps of less than 100 μs are generated in order to achieve, among other things, high measuring frequencies.


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