[Antennas] Current Flow in Coax?

Fri Sep 28 00:59:35 EDT 2012

> I understand this must be the case to cancel radiation from the coax, but can
> someone point me to a technical explanation of how the forces operate to "pull"
> the current to the inside of the shield?

One way to look at it is this:
If the electric and magnetic fields are properly contained within the
coax and none are on the outside, then those fields ... which are what
cause the current to flow ... can only move electrons on those
surfaces they touch ... namely, the inner wire and the inside wall of
the shield. The RF fields themselves do not penetrate through good
conductors, so the fields that are inside, can't move electrons on the
outside wall of the coax shield.
The only way to get current on the outside of the shield, is for there
to be (electro-)magnetic fields on the outside of the coax. Likewise,
the reverse is true; the two go hand-in-hand. Wherever there is RF
current, there are electro-magnetic fields adjacent to it, and
vice-versa.
The way I see it, the forces do not precisely "pull" the current to
the inside of the shield. Rather, there is nothing there (no fields)
on the outside of the shield, or many skin-depths into the metal
thickness, that could make current flow there. So the result is that
the current ends up being confined mostly to the inner wall, not
precisely that it was "pulled" there by some sort of force.
Andy