[Animats]

I wondered about that, too. There's a worldwide ISM band at 5.725 to 5.875 GHz in which you can run radars. But he says he's sweeping from 5.2GHz to 6 GHz. That's a lot of spectrum to be using. There's lots of stuff in there, including satellite links and aeronautical radionavigation.

Here's a similar project which is in the 5.8 to 6 GHz range. With a little work, they could probably make it stay in the ISM band there. One big frustration of gigahertz RF work is that the test gear you need to see what's happening costs far more than the project. I tried to build a frequency-modulated LIDAR once, and ran into that.

[1] https://hackaday.io/project/1682-simple-low-cost-fmcw-radar