A traffic sensor is mounted at a fixed location to monitor multiple lanes of traffic. The traffic sensor (a) generates a programmable time-varying modulating signal; (b) generates a modulated microwave signal based on the programmable time-varying modulating signal; (c) radiates the modulated microwave signal in a radiation beam at an object; (d) provides a proportional calibration signal based on the modulated microwave signal; (e) measures parameters of the calibration signal, and (f) corrects the programmable time-varying modulating signal based on the parameters of the calibration signal.