Frequency conversion in the ionosphere for over-the-horizon radar

Generation of low-frequency signals in the ionosphere has direct applications for over-the-horizon radar and related processes. The mechanism proposed in this study uses a ground-based modulated rf signal to resonantly excite plasma oscillations in the ionosphere's F layer, creating low-frequency signals that propagate back to the earth's surface. The authors find that a 94-GHz signal, modulated at 9 MHz and operated at 1 MW, can generate a 9-MHz signal on the ground, 500 km from the interaction regime in the ionosphere, at intensities sufficient for detection. This points to practical mobile radar units and atmospheric monitoring.