[Lf] [Fwd: LF: Ground loss/gain (was: polarization of small loops)]

[Andre Kesteloot]

Claudio Girardi wrote:

> Hello all,
> I think that the "ground gain" and the "ground losses" depends on two different
> phenomena. Ground gain should come from reflections from ground at a distant point
> (far field) from the source combining with the direct ray from the same source with
> the proper phase. The type of antenna used shouldn't matter since it will be seen
> as a point source at a large distance; of course the polarization w.r.t. ground
> will be important.
> The ground losses depend on the presence of dissipative materials near the antenna
> (near field); for a small electric dipole the electric field near the antenna
> should be more intense than for a small magnetic loop. On the other hand, the
> magnetic field near a loop antenna should be higher than for an dipole. At a
> distance (far field) there is no difference between the two (for the same radiated
> power, of course). So probably for a monopole it is important to have a dielectric
> with low losses (and ground usually is not), while for a loop a lossy dielectric
> near the antenna has less effect, due to the weaker electric field. But I have no
> idea how lossy is the ground as a magnetic material...
>
>                   73 de Claudio, IN3OTD
>
> Rik wrote:
> >And to make things more complex, what about a loop close to a
> >not-so-perfect ground plane ?
> >Either the loop is not (or little affected) by the ground. That means
> >little or no groundloss (as is claimed by some) but at the same time it
> >would mean that the loop will also not benefit from any "ground gain".
> >On the other hand, if the loop benifits form significantly from
> >"groundgain" then I would expect that the loop would also suffer from the
> >groundlosses, as a vertical monopole does.
> >
> >Any clues ?