FMCW

FMCW stands for frequency-modulated continuous-wave. It is a radar technique that transmits a continuous signal whose frequency is swept over time, producing a chirp. A portion of the transmitted signal reflects from targets and returns to the receiver. The received signal is mixed with the transmitted signal to produce a beat frequency that is proportional to the round-trip time delay. From the beat frequency, the distance to the target can be calculated.

The range resolution in FMCW radar depends on the sweep bandwidth B: ΔR ≈ c / (2B). Wider bandwidth yields finer resolution. The same processing can also estimate relative velocity by analyzing Doppler shift or phase progression across multiple chirps, enabling simultaneous estimation of range and velocity.

FMCW is widely used in automotive radar, altimeters, industrial sensing, and some airborne or maritime radar systems. Modern automotive implementations commonly operate in mm-wave bands such as 77 GHz or nearby frequencies, offering high resolution and short-range detection capabilities.

Advantages of FMCW include continuous transmission for high sensitivity, coherent processing for precise velocity estimation, and the ability to achieve high range resolution with broad bandwidth without requiring high peak power. Disadvantages include the need for highly linear, stable chirps and precise timing, potential range-Doppler ambiguities, and susceptibility to multipath and clutter in complex environments.