On the Maximum Unambiguous Range of LFMCW Radar

The unambiguous range of a radar is the maximum range at which a target can be located so as to guarantee that the reflected signal/pulse from that target corresponds to the most recent transmitted pulse. It is an important factor for radar. Different modulation patterns of Linear Frequency Modulator Continuous Wave (LFMCW) have different maximum unambiguous range. For an easy way to calculate the factor, Single Period Ambiguity Function (SPAF) is proposed to analyze the unambiguous range of LFMCW radar. The receiver of a LFMCW radar can be analysed with SPAF. By analyzing cuts of SPAF along small Doppler shifts of symmetrical sawtooth LFMCW radar, it is demonstrated that its maximum unambiguous range will correspond to the shift equal to half of the modulation period. And the maximum unambiguous range of arbitrary LFMCW radar is αT (T is the period, and α is the symmetrical factor, 0<α≤1). With this result, it is easy and intuitional to calculate the maximum unambiguous range of LFMCW radar.