  Target classification is an important task of automotive radar systems. In
this work, a concept for estimating the height of vehicles to allow for a
differentiation between passenger cars, trucks, and others, is presented and
discussed. Fixed installed radar sensors for traffic monitoring in the 77 GHz
band are used to track and analyze radar echoes from individual vehicles as
they move relative to the radar. Considering multipath propagation, which
includes the ground reflection, the height of individual radar targets is
estimated by analyzing the periodicity of the resulting amplitude modulation
(AM) of the echo signal as a function of the horizontal distance from the
radar. Two approaches have been realized to integrate the concept into an
automotive FMCW signal processing scheme. Measurements in a test field using a
trihedral corner reflector as an idealized target in heights from 0 to 2.5 m
suggest, that the concept is suitable for height estimation in an automotive
context.
