I read a lot about passive radars trying to leech off of opportunistic waves, and lots about actual troops preferring to play hide-and-seem with anti-radiation weapons just to use active machines.
A config that strikes me as obvious but doesn’t seem to be popular would be just bistatic where you fire your own transmitter far away from yourself?
There’s got to be a reason, but it seems like best of both worlds.
Much more covert, and civilian infrastructure also less likely to be blown up.
Probably more complicated to setup in a hostile environment because you'd need multiple transmitters, which also need to remain stationary, or at least you need to accurately know when they move.
We've already got a really extreme version of this.
https://en.wikipedia.org/wiki/GNSS_reflectometry