A delta-sigma transmitter based heterodyne FMCW radar

We present a heterodyne frequency-modulated continuous-wave (FMCW) radar system operating in W-band with a bandwidth of 3 GHz. The architecture is based on a binary phase-shift keying modulator in combination with a delta-sigma modulator. These components are used in the transmit (TX) path of the radar. In this way the frequency of the TX signal can be shifted arbitrarily, which allows to freely choose the center frequency of the radar output signal. This offers several advantages, especially for short-range applications. Compared to a conventional FMCW radar the complexity of the novel system is only slightly increased due to the added components. Measurements, carried out using a transceiver together with antennas in package, demonstrate that the noise shaping together with a suitable signal processing technique leads to a signal-to-noise ratio which is only 4 dB below a purely homodyne system for moderate target distances. However, considering very closely spaced targets it is shown that the heterodyne radar even outperforms its homodyne counterpart.