Re: Ground wave transmission, was G-line

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: Ed Phillips <evp@xxxxxxxxxxx>

" > I understand about the buried antenna but question the image
 > antenna bit.  That analogy applies to the radiation pattern
 > of an antenna above a perfect (infinitely conducting) ground
 > plane but not to an antenna embedded in lossy soil.

I think Robert is right.  After all, the antenna above a ground
plane is just a special case of an antenna above a boundary
between two dissimilar materials.  If there's a difference in
dielectric constant or specific resistance, there'll be partial
reflection from the boundary, and you can always consider the
reflected component to originate from an imaginary mirror of the
antenna."

	The issue is to the reflection coefficient at the boundary.  If there
really was a wave propagating in the earth (at the normal "buried
antenna" depths I've seen quoted - a few feet) then there is indeed a
discontinuity at the boundary between the earth and the air above it,
but I don't know how to calculate how much power is reflected BACK INTO
THE EARTH from that discontinuity.  In the case of the "image antenna"
for an antenna above a [perfectly conducting] earth all of the power is
reflected at the boundary.  In the case of "real earth" that is by no
means true and in attempting to calculate the vertical pattern of an
antenna above earth (or the loss in distant transmission due to
multipath reflections from the ground) it's necessary to know both the
real and imaginary parts of the ground conductivity.

	Bottom line is that I still don't think there's much of an "above the
earth" image antenna for a "typical" underground antenna.

Ed