Effects of Reference Frequency Harmonic Spurs in FMCW Radar Systems

Harmonic spurs in local oscillators can degrade the performance of millimeter-wave frequency-modulated continuous-wave radar systems that employ a large-ratio frequency multiplier for LO generation. In this paper, we analyze the effect caused by harmonic spurs on system performance. Undesired spurs show up alongside the beat-frequency component in the de-chirped intermediate frequency spectrum, which deteriorates the system dynamic range (DR). The dynamic range can be accurately predicted by our model, and the measurement results of a 24-GHz radar are presented as a proof of concept. For high-dynamic-range radars, a harmonic rejection ratio of DR/2 in dB-scale is required for a given dynamic-range budget. A design example is presented with a 55-dBc harmonic rejection ratio, and it offers a 100-dBc spurious-free dynamic range.