Low-Angle Tracking by Carrier-Free Radar

Multipath transmission is currently the most important limitation for the accuracy of low-elevation-angle radar. The use of properly polarized nonsinusoidal electromagnetic waves permits one to discriminate between the wave that propagated directly from the radar to the target and back, and all the other waves that propagated via the surface of the earth, either on the way to the target or on the way back (first-order multipath transmission). The effect works both over water, a good conductor, and over dry land, a good insulator. It appears that the error due to first-order multipath transmission can be essentially eliminated. As a fringe benefit, one avoids the enormous propagation losses incurred when pulses with a duration of about 1 ns are transmitted with the help of a sinusoidal carrier. (A similar polarity-reversal effect, that exists for circularly polarized sinusoidal waves, cannot be used for an all-weather radar because of the high absorption losses.)