“Even a horn has diffraction sidebands, and unless they're all at least 8dB down in all situations that's bad. The laser trips won't cover this.”

I don’t really understand this. My guess is that they’re saying that besides the targeted microwave band, other high/low frequencies will be emitted (sidebands) and that these will diffract and be way outside of the directional beam that’s protected by the laser trip wire.

I would assume the inventors have at least some explanation for this, but a fluffy article won’t go into those details.