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This is similar to how a metal box blocks radio waves, and how x rays can still penetrate it.

What kind of metal? I thought X-rays couldn't penetrate lead.

https://www.researchgate.net/post/How_does_the_plasma_sheath...

> an electromagnetic wave can penetrate the plasma if the wave frequency f is higher than the electron plasma frequency.

X-rays have a much higher frequency (i.e. much higher energy) than the radio waves we normally use for communications, so it can punch through the noise of charged particles that makes up plasma.

I believe it's not a matter of "noise". Rather, metals and plasma are conductive up to a certain frequency. Beyond that frequency, resistance goes up and the material becomes transparent. This is basically because the electrons can't "keep up" with the electric field's oscillation so they are ineffective at screening it.

It is actually pretty simple. Plasma is conductive. Most conductive things Will block radio waves at GHz and below

If it is conductive, can't you make it part of the antenna?

yes -- https://en.wikipedia.org/wiki/Plasma_antenna