[Darksheare]

An EMP would work. And it wouldn't even be nuclear to start with. We developed an EMP a couple years back, has energised copper coils inside it packed around a couple HE charges. When the HE goes, the coils collapse and an EMP pulse is produced. (VERY brief and as undescriptive as possible. Don't want to be helpful to anyone other than us.)

A passive radar would be just as sensitive to an EMP pulse as any other electronic system. Not to mention, the local power grid would suffer dramatically.

[steveegg]

You're even more devious than me. Those long antennas required to make the system work make REAL good EMP wave guides.