What does an FMCW radar twin without range–Doppler coupling get wrong about a moving target?

research/chirp-twin

FMCW range–Doppler coupling: a twin that reads true range misses a bias of f_D T cells (0.6–4.8 at 30 m/s), signal-level check ≤1e-4 cells, wrapped-Doppler compensation is worse than none on half of the over-range speeds, and a ±60° stationary scene leaves 0.71κv position bias plus 0.46κv distortion.

9 tests

What it found

A sawtooth chirp radar reads a moving target’s range as R + κv, κ = f_cT/B; the twin reads R. A signal-level beat-tone simulation matches the formula to ≤ 10⁻⁴ range cells, and the bias is f_DT cells independent of bandwidth: 0.6, 3.1 and 4.8 cells (9 cm, 46 cm, 2.9 m) at 30 m/s for fast 77 GHz, mid 77 GHz and slow 24 GHz ramps. Within the unambiguous speed it is under half a cell, but compensating with the radar’s own wrapped Doppler is worse than doing nothing on exactly half of the over-range speeds. For a stationary scene (±60°) a centroid fit absorbs 0.71κv of along-track position error and leaves 0.46κv rms distortion. Stylised: single up ramp, noise-free tone, no radar data.

A figure from its own output

Figure produced by research/chirp-twin: compensation — chirp-twin/experiments/compensation.svg, written by the project's own experiment code.

Paper, code and results

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Produced with AI assistance (Claude). Results are from the code in this repository and are simulated or stylised unless the abstract says otherwise; nothing here implies affiliation with or endorsement by any lab, researcher or company cited. MIT licensed.