Spurs in Millimeter-Wave FMCW Radar System-on-Chip

In this article, we present a nonlinear system model to evaluate the impact of circuit nonlinearities on spurs in millimeter-wave frequency-modulated continuous-wave (FMCW) radar system-on-chips. The developed model includes the harmonics of the frequency multiplier, nonlinearity of the power amplifier (PA) and low-noise amplifier (LNA), the switching operation of the receiver (RX) mixer, the limited bandwidth of the PA, LNA, transmitter (TX) and RX antennas, as well as the TX-to-RX leakage. The developed nonlinear model can be used to derive the frequency and amplitude of spurs in the radar IF spectrum. The major insights about the impact of different nonlinearities and their interactions are as follows: 1) harmonics of the frequency multiplier appear as spurs in the IF spectrum; 2) PA can be driven in its nonlinear region to mitigate the harmonics generated by the frequency multiplier; 3) bandwidth of the TX and RX systems should be limited to attenuate the undesired harmonics; and 4) interaction between the TX-to-RX leakage signal and the LNA nonlinearity can lead to spurs close to the target echo in the IF spectrum.