Comment by topspin

> More modern over the horizon radars do work, but have much more compute power behind them.

Yes, and it also requires exotic clocks.

A few years ago, a story appeared about the Australian JORN over-the-horizon radar system. The University of Adelaide developed a highly precise cryogenic sapphire oscillator with jitter measured in attoseconds. The oscillator enhances radar performance by improving measurements of Doppler phase shift. They claim this oscillator is the highest precision clock yet created.

Despite all the downsides of OTH radar, it's still under active development and in the field.

https://www.adelaide.edu.au/ipas/real-world-impact/defence-s... https://spectrum.ieee.org/for-precision-the-sapphire-clock-o...