Using FMCW Doppler Radar to Detect Targets up to the Maximum Unambiguous Range

Most applications of frequency-modulated continuous-wave radar described in the literature involve targets that are in relatively close proximity to the radar. In these cases, the round-trip travel time of the target's radar signature is small relative to the transmit chirp duration, simplifying the processing required for range and velocity extraction. This is not the case for more distant targets, where much of the radar signature is received after the start of the subsequent transmit waveform. In this letter, we examine various signal-processing options for coping with this long-range condition. We analytically demonstrate how to retain both range and Doppler shift information for an arbitrary number of targets spaced anywhere from very near the target up to the radar's unambiguous range. The motivation for this work is to develop a 95-GHz Doppler radar for measuring ice and dust particle dynamics in cometary jets. Simulations and experimental results are provided to validate our methods.