At 02:32 PM 10/23/2005, Joe Giacobello wrote:
>I am thinking about using ladderline for a folded dipole or for linear
>loading a wire antenna. I wonder if anyone has successfully modeled
>ladderline and, if so, what parameters they used for the insulation. I
>assume that the insulation is PVC, but what is the thickness and how are
>the alternating windows accounted for?
>
>I'd appreciate any information that members of the reflector can provide
>on this subject.
>
>73, Joe
>K2XX
what program are you using to model it?
If NEC, insulation models assume uniform thickness around the conductor,
which is not representative of ladder line, so the "fine scale" details of
the field in proximity to the ladder line will not be correct.
Since the windows are very much less than a wavelength long, you can
probably model it as a suitably insulated pair of wires with insulation
properties chosen to match the actual properties of the wire.
Even better, you could probably represent the ladder line as a suitably
built NT card for the transmission line properties, and a single insulated
wire to represent the "common mode" properties.
If you're hoping to model the effects of things within, say, 5 times the
cross sectional size of the ladder line, NEC is probably not a good tool.
You need something like HFSS or one of the other programs that models
dielectrics. Method of Moments (MoM) just isn't all that great at handling
dielectrics.
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