The basic principle underlying Over-The-Horizon, Backscatter (OTH-B) radar. The ionosphere deflects an outgoing HF (High Frequency) signal emitted by an OTH-B radar. This natural "bank shot" allows the radar to search for targets that lie over the line-of-sight horizon. If the signal is then reflected by an object, the return will again bounce off the ionosphere. Each change of direction scatters the signal even as its passage through the atmosphere attenuates it. Moreover, the ionosphere constantly changes (which affects back-scatter) and requires close monitoring to determine the best HF frequency to use.

Radars using the back-scatter principle have large antenna and must extensively process the return to delete all other scattered echoes (e.g., land and sea clutter) to detect the target.