I'm afraid your Faraday screen might not work quite like you think it does.

In the vicinity of the screen, the E field is indeed reduced. However,
you haven't stripped off the E field from the EM wave, or separated it.
The E field is largely reflected from the screen, but out of phase with
the original wave. So the E/H ratio is smaller on *both* sides of the
screen. Close to the screen, much of the energy formerly in the E field
has been transferred to the H field. But as you go beyond the screen in
either direction, you'll find the E field increasing and the H field
decreasing as the energy redistributes itself. Within a short distance
(typically considerably less than a wavelength, but depending on the
size of the screen), the ratio of E/H will again be close to 377 ohms,
assuming air is the surrounding medium. The Faraday screen works in the
broadcast application only because the "shielded" component is close to
the screen, where the E/H ratio is low.

In other words, you can modify the E/H ratio in a small region of space
by moving the energy from one to the other. But you can't separate the
two components or eliminate one or the other.

This is of course referring to time-varying, not static, fields. Reg's
statement is technically false, since he didn't say whether the fields
are time-varying -- static E and H fields can independently exist. But
time-varying E and H fields, which I'm sure is what he meant, can't.

Roy Lewallen, W7EL


Richard Harrison wrote:
Reg, G4FGQ wrote:
"It is impossible for an E-field to exist without an H-field."

Agreed.

By definition an electromagnetic wave includes an electric component and
a magnetic component. That does not mean the components are inseparable.

The purpose of a Faraday screen is to eliminate capacitive coupling
while permitting magnetic coupling.

I`ve worked in several medium wave broadcast plants. In these, each
tower was coupled through a 1:1 air-core transformer to its transmission
line. The transformer consisted of two identical coils, one on either
side of a Faraday screen. The coils shared a cmmon axis.

Electrically, the transformer was transparent at the transmitting
frequency. It coupled the transmitting frequency as if the transformer
did not exist to impede. Its purpose was to eliminate capacitive
coupling, The Faraday screen provided a place where electric field lines
are shunted to ground.
The problem with capacitive coupling between a transmitter and a tower
is that the higher the frequency, the less the reactance or opposition.
The coupling is better through a capacitance to the harmonics of a
frequency than it is for the fundamental. The Faraday screen removes
this unwanted bias for imroved harmonic propagation.

A side effect of the Faraday screen is that it removes lightning strokes
before they reach the transmission line from the tower.

The Faraday screen looks like a metal rake. Its back where the teeth or
tines join is firmly grounded. The teeth are open-circuited. Current
cannot circulate between and through the teeth, so no counter
electromotive force can be generated to oppose magnetic coupling between
primary and secondary coils. The rake is transparent for magnetic
coupling but it is a stopper for electric coupling.

By complete shielding, that is metalllically enclosihng one or both
coils of an impedance coupling pair, magneric coupling between them can
be practically eliminated. A coupling capacitor between the coils allows
only the electric field to be effective. There`s no magnetic field
involved.

I`m no advocate of the E-H antenna, but the electric and magnetic
components of a wave are easily separated.

Best regards, Richard Harrison, KB5WZI