[TowerTalk] Modeling Ladderline as an Antenna Element

[Jim Lux]

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.