ilias 🏴☠️💙💛check out this very interesting project: an open-source DIY phased array radar system with coverage up to 20 kms. fascinating that such tech can now be assembled & set up on a budget (more or less) – as long as you have required licence, which AFAIU isn't like ham radio one
this DIY drone detection project meanwhile goes even further in reducing the cost, by using acoustic sound - although I think it's likely to be less effective