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Old November 10th 04, 05:48 AM
Richard Harrison
 
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Art Unwin wrote:
"So how does one "create" several conductive surfaces of what ever
length on a continuous electrical surface?"

First examine the ways it has already been done and ask why? A
non-resonant reflector provides a much wider bandwidth than a resonant
reflector as used in an array like a yagi, for one thing.

Plenty of grid-dish, corner-reflector and similar non-resonant reflector
antennas are in use to reduce wind-loading. You have no need at lower
frequencies to use solid reflectors. Surface irregularities are not much
problem. The solid dishes at 2-GHz are built that way for convenience,
not because they need to be. The same is true at lower frequencies. At
higher frequencies, the conductors are so close together, there isn`t
enough reduction in wind-loading to be worth the construction effort
required with grid-reflectors.

Grid reflectors only need a collection of conductors parallel with the
radiating element(s) illuminating (driving) the antenna, and placed for
best results. Reflecting elemants in a grid reflector placed
perpendicular to the driven element don`t work. Curvature is used tn
dish reflector bars for focus. An angle is used in the corner-reflector
for more gain than a flat reflector. None of the reflectors needs
cross-connections between the reflector bars anymore than ground radials
need their far-ends interconnected. Such connections allow eddy currents
which only cause loss. The only current of value is that in the
direction of the ground radials or in the direction of the reflector`s
parallel conductors, as the case may be. So the eddy currents are bad.

Spacing between reflector bars is related to wavelength and capture
area.. Measure it in a good grid antenna and scale to your frequency.
Or, see Kraus for capture area etc.

Best regards, Richard Harrison, KB5WZI

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