length. For want of a better word its image has to be a perfect conductor
for the antenna system as a whole to be 100% efficient.
The invocation of "image" into efficiency or ground losses shows a
misunderstanding of antenna basics.
We were taught how to use antenna "images' in EM theory back in the 1970's,
because computers were uncommon and there weren't any modeling programs. The
antenna "image" is nothing but a tool to aid in pattern calculation. It
isn't applicable to radial systems, ground losses in verticals, or anything
similar.
The "image", as applied to antenna systems, represents the overall effect of
re-radiation from the ground around an antenna. With a vertical, this area
extends out for a considerable distance from the antenna. The amplitude and
phase of a completely fictitious "image" is use to calculate field intensity
at different points in space, just as if two antennas were being phased in a
certain phase and current amplitude relationship.
A problem occurred, because people started to think the image was an actual
"thing" that existed at one point or area in the earth, and that allowed
them to create false ideas in their heads of what an image is. The image
antenna is a fictitious tool for estimating patterns, nothing else.
73 Tom
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Topband reflector - topband@contesting.com
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