Al Williams wrote:
> If I am reading this response correctly, then any metal anywhere
> decreases the radiated field from the driven element?!
>
> I am not discussing directivity loss or gain--I am just curious
> of whether the field in the vicinity of metal absorbs some of
> the field and somehow that causes the total field of the driven
> element to be reduced.
>
>
No.. not decrease, necessarily... "change" is the operative word.
Any conductor (or dielectric) will change the current distribution (and
if it's a conductor, it will have a induced current distribution of its
own that radiates). The effect is distance sensitive, of course,
farther away=less effect.
After all, that's how a Yagi-Uda works. The current in the driven
element couples to the parasitic elements, and the net of all the
currents is what determines the pattern.
The field of the driven element might be higher or lower, depending on
the coupling and how much energy is stored in the near field of the
elements.
In a superdirective array (most high gain yagis fit in this category),
the currents are higher than they would be in a dipole with the same
input power (i.e. there's more stored energy)
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