Low-Cost X-band Doppler Radar for Nadir Velocity Detection

The low-cost, low power, small X-band (10.5 GHz) Doppler radar module HB100, was designed and is used commercially for movement detection. As with most radars, radial displacements of targets provide positive or negative Doppler shifts – depending whether they are approaching or receding in the radial direction. However, in many applications the movement tangential to the radial direction is of interest as well. The radar return from a short steel pipe (outer diameter 170 mm) rolling at a constant velocity on a horizontal plane was used to investigate the effect on the radar output as the pipe rolled through the E-plane and H-plane radar beams. Given the finite beamwidths (40 degrees and 80 degrees, respectively), the voltage output signal versus time is symmetrical with respect to the Nadir in both the approaching and receding part of the trajectory of the pipe for uniform displacement perpendicular to the radar beam. With a null recording immediately beneath the radar in both planes, the velocity of the pipe is monotonically related to the time between the two major peaks and troughs. This allows the velocity determination of objects moving through the radar beam tangentially.