FMCWradar

FMCW radar, or frequency-modulated continuous-wave radar, is a radar modality that transmits a frequency-modulated continuous waveform, typically a linear chirp, and determines target distance and relative speed by mixing the received echo with a copy of the transmitted signal. Unlike pulsed radars, it continuously transmits while listening for echoes, enabling high update rates and compact hardware.

In a typical FMCW system, the transmitter sweeps its frequency across a bandwidth B during a sweep period Tc. The echo from a target at range R is delayed by τ = 2R/c, where c is the speed of light. Mixing the received signal with the transmitted signal produces a beat frequency fb, approximately equal to fb = kτ = 2Rk/c, where k = B/Tc is the chirp rate. Range is inferred from fb, while an additional Doppler shift caused by target velocity provides velocity information. Range-Doppler processing across successive chirps yields estimates of distance and radial speed.

Key performance characteristics include a range resolution ΔR ≈ c/(2B), determined by the sweep bandwidth, and the ability to extract velocity from Doppler information without requiring short pulses. The technique enables fast, accurate sensing with relatively simple front-end electronics and high average power efficiency, though it requires stable oscillators and careful clutter and interference management.

Applications span automotive safety systems (adaptive cruise control, collision avoidance), industrial and process sensing, robotics and unmanned systems, and level or distance measurements in harsh environments. FMCW radar remains a popular choice for compact, high-update-rate sensing in short- to medium-range regimes.