Continuous vs. pulsed
Traditional radar sends a short pulse, waits, listens. FMCW never stops transmitting. It sends a continuous tone whose frequency sweeps up and down linearly. The echo returns at the same time, offset in frequency by exactly the round-trip delay. That offset is directly proportional to distance — no timing circuits needed.
Doppler for free
If the target is moving, the Doppler shift adds a second frequency offset. Because the chirp is linear, the beat frequency from delay and the beat frequency from Doppler sit at different places in the spectrum. One FFT separates them: distance from one peak, velocity from the other. Two measurements, one chirp, zero ambiguity.
77 GHz and 24 GHz bands
Automotive FMCW lives at 77 GHz for long-range adaptive cruise (up to 250 m) and 24 GHz for short-range parking assistance. 77 GHz antennas are tiny — a few millimetres — so several can fit in a bumper array, giving angle measurement via phase comparison across the array.
From luxury to law
Adaptive cruise was a Mercedes S-Class option in 1999. By 2022, EU regulations required automatic emergency braking on every new car. Pedestrian and cyclist detection, lane-change assist, cross-traffic alert — all powered by FMCW chips from companies like NXP, Infineon and Texas Instruments.