NEC-LIST: conical spiral: impedance convergency

Hi,

I am modelling a conical rectangular spiral antenna for
my thesis project. The nec-input file is generated
by a perl script I have written. I have problems
to see any impedance convergency, although the
models went from just about 100 segments to over 3000.

I sense that this might have to do with the
unequal segmentation on parallel wires, even though
the wires are at least hundreds of wire radii apart.

Another factor might be the feed arrangement.
I have currently two options:

1. The feed wire is diagonal and connected
in the corners. This leaves a 45 degree angle.

2. The feed wire is parallel with the following
spiral arms - 90 degree angle.

Which feed arrangement would
be more accurate for NEC?

Does anyone have an idea how I could
guarantee accuracy for the model,
or how I change the model to get impedance convergency?

Best regards,
Alexander Witte

Electromagnetic Engineering
Royal Institute of Technology
Stockholm, Sweden

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