[TowerTalk] [Bulk] Re: Flat plate compensation

[Jim Lux]

On 3/13/15 1:42 PM, Grant Saviers wrote:
> Lawson  "Yagi Antenna Design" page 7-12 computes the equivalent radius
> of a boom to element plate as  =width/4.  So if you make the center
> element as long as the plate and width/2 diameter, the modeling should
> be close.   He also states "element length should be increased 6 percent
> of boom diameter" when they are electrically connected.  Both are pretty
> small effects for HF antennas, but if you are doing modeling, why not
> include it?
>

This is very close to the guideline for modeling flat surfaces in NEC 
using wires: make the wire diameter such that the circumference of the 
wire is the spacing of the wires.

Wire diameter (particularly near the feedpoint or center of a resonant 
element) doesn't have a strong effect on the EM properties.  It's all 
about the current there, and whether the current is spread out or not, 
it generates the same field at a few meters away.

Where it would start to make a difference is if you have very closely 
spaced elements (so the mutual coupling of the segments is high).  If 
you were modeling something like a gamma match, the physical 
configuration gets important.