  A new method of distortion mitigation for multitarget interferometric angular
velocity estimation in millimeter-wave radar is presented. In general, when
multiple targets are present, the response of a correlation interferometer is
corrupted by intermodulation distortion, making it difficult to estimate
individual target angular velocities. We present a distortion mitigation method
that works by decomposing the responses at each antenna element into the
responses from the individual targets. Data association is performed to match
individual target responses at each antenna such that cross-correlation is
performed only between associated targets. Thus, the intermodulation distortion
(cross-terms) from correlating unlike targets are eliminated, and the result is
a frequency response whose individual frequencies are proportional to the
angular velocities of the targets. We demonstrate the approach with a custom 40
GHz interferometric radar, a high-accuracy motion capture system which provides
ground-truth position measurements, and two robotic platforms. The multitarget
experiments consist of three scenarios, designed to represent easy, medium, and
difficult cases for the distortion mitigation technique. We show that the
reduction in distortion yields angular velocity estimation errors in the three
cases of less than $0.008$ rad/s, $0.020$ rad/s, and $0.033$ rad/s for the
easy, medium, and hard cases, respectively.
