...and would the windows have to be shielded too?
As an avionics maintenance engineer, I have sat in the cockpit of a Classic 747, operating a portable ILS Test Set which transmits low power ILS test signals from an attached wire antenna placed on top of the lightshield. It allows me to produce fly up/down & left/right signals during Autoland tests. I have used this test set in an area where there is little opportunity for test signals to be reflected off buildings and metallic objects. How the signals curve around the nose of the aircraft to the aircraft's receiving antennae on the nose gear/tail is beyond me (or are they reaching the antenna by line of sight.... going through several layers of aluminium to get the antennae?).
What are the odds of a faulty portable device beaming signals out of a cabin window and having those signals bounce off an engine cowl or wing towards an ILS antennae? (producing a subtle fly-down signal on approach on a foggy day). There is no way of preventing these signals reaching the aircraft's external antennae unless the windows are also shielded.
Rgds.
Q.