Just to be clear, since the discussion drifted to half-wave radiators, my
comment above was specific to the modeling of thick v. thin half-wave
radiators, including the 180-195 degree radiators of some well-known 50KW
AM stations. The results when modeling the base Z of approx. 1/4-wave
radiators is less affected by thickness, probably due to a lower base Z to
start with.
The theory (or cause) behind this is twofold:
1.) A thicker radiator at an end has a larger area for the electric field.
This results in a less concentrated e-field discontinuity or boundary at the
open end of the element. In other words the electric field is not as
intense, and that means voltage is less.
2.) Any antenna is also a transmission line. The surge impedance of that
transmission line is lower with a larger effective diameter conductor. The
mismatch of the open circuit at the far end is transformed through that
transmission line, by the standing wave in the antenna, to a new lower
impedance at the center, just as the center can be transformed back up to an
open end.
This means a thicker antenna element doesn't have the low and high impedance
extremes at the open end or along the antenna that a thinner antenna has.
The standing waves are muted.
If the antenna had no radiation or loss, it would have no end current. It
would have infinite impedance.
This applies to counterpoises also.
We can see how difficult it is to have useful things in antennas (antennae
are found on insects, and can have zero current) that have no radiation and
no loss. :-)
73 Tom
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Topband reflector - topband@contesting.com
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