A Delta-Sigma modulator-based heterodyne FMCW radar for short-range applications

We present a heterodyne frequency-modulated continuous-wave (FMCW) radar, applicable in short-range applications. Owing to a modulation of the transmit (TX) signal, the intermediate frequency (IF) signal can be shifted away from zero frequency to reduce the influence of dc-offsets and low-frequency disturbances like, e.g. flicker noise existing in components like mixers, amplifiers and analog-to-digital converters. The presented system is based on E-band transceivers realized in SiGe technology, which are fully integrated with antennas in a plastic package. A sinusoidal modulation of the TX signal is realized by a binary phase-shift keying modulator, which is controlled by a Delta-Sigma sequence. The choice of a sinusoidal modulation allows to reuse signal processing blocks which are typically available in FMCW radars. Measurements show that the achievable signal-to-noise ratio is comparable to a homodyne realization since the Delta-Sigma noise can be filtered in the IF stage. Experiments with a bandwidth of 8GHz demonstrate measurements down to 12cm with standard deviations of the measured ranges lower than 60 mu m. Compared to a homodyne realization the blocking distance could be reduced by approximately 40mm.