I. Introduction
In MFCW(Multi-Frequency Continuous-Wave) ranging systems, distance is extracted from the phase shift of a group of sinusoids named sidetones[1]. The sidetones are generally transmitted in turn by angular modulation (FM or PM), so their extra phase shift brought by the transceiver channel will cause the main system error for distance measurement. Owing to the nonideal channel characteristics, the phase of the demodulated sidetone will change with carrier frequency drift and power variation, introducing varying system error that is difficult to be eliminated by calibration. The whole system must be carefully analyzed and designed to constrain it within an acceptable range.