Does the addition of a static charge or magnetic field to an antenna affect the EM waves it's supposed to receive? I read this:
Does laser beam (EM wave) affect magnet next to it?
But I distinctly remember the use of a magnetic field to alter the polarization of light. Doc Edgerton used this technique to create a very fast shutter to capture the first milliseconds of a nuclear explosion. So it would seem magnetic fields DO interact with EM waves. Or is it a CHANGING magnetic field that interacts w EM waves?
Also, if a VanDe Graff Generator is used to a put a massive static charge on an antenna, does increase its gain? reduce its gain? Is there any experimental data about this or do I have to do the experiment?
 A: The so-called Faraday rotation, or magneto-optic effect, is an interaction between a magnetic material and linearly polarized EM wave, see https://en.wikipedia.org/wiki/Faraday_effect. The rotation in question is the turning of the linear polarization of the EM wave (light) that is moving within a homogeneous magnetic material and in a parallel direction with the external static biasing field. The amount of rotation is proportional with the length of propagation in the material but the proportionality depends whether the motion is along in the direction or is in the opposite direction of the static bias field.
The effect can be quite large and various control circuits (isolators, circulators, switches) are based on this principle.
As regards the static electric charge, if it is frozen in a dielectric that is cannot move within the material that holds it, then it has absolutely no effect on an incident EM wave. On the contrary, if it can move, say freely because it is deposited on a metal surface that is dc-wise insulated, then yes because the charges can only accumulate on the surface of the metal and the incident EM wave can move and accelerate them that causes reradiation. And in fact, this reradiation can be observed on any RF antenna as it is interacting with the surrounding metal surfaces (ground planes, outer skin of the coaxial cable, other metal objects, etc.) and you get an uncontrolled and unexpected radiation pattern.
