Vertical digital beamforming versus multipath height finding

This paper assesses the advantage of exploiting radar wave multipath propagation to measure the height of extended objects using a Frequency Modulation Continuous Wave (FMCW) automotive radar. The proposed height estimation algorithm utilizes the non-line-of-sight (NLOS) propagation from a target to calculate the height of objects in the vehicle's surroundings without requiring multiple antennas at different heights. First, a multipath propagation model is presented; a target height formula is derived based on sensor-target geometry. It is then shown from the derived height formula that the height estimation accuracy of the algorithm depends greatly on the range resolution of the sensor. Next, scattering mechanisms of radar waves, wave diffraction in particular, are discussed to make the multipath propagation model valid for extended targets. Finally, the results of a measurement campaign conducted on extended targets of different heights are discussed and compared against the results of a Digital Beamforming (DBF) algorithm applied to a vertical antenna with eight channels. The proposed algorithm resolves target heights very accurately, achieving an average mean height estimation of 0.025 m for curbstones 0.11 m high.