Re: NEC-LIST: Dipole Arrays

I couldn't cut and paste conveniently, so here is my paraphrase of
Robert Green's question about Franklin arrays, which are a series of
colinear dipoles with phasing lines between the dipoles. He got a lot
of beam tilt. Judging from his input deck, he used 1/2 wave TL's
between the elements.

This is most likely because there is a lot of mutual coupling between
the elements (which are only lambda/2 apart), and the 1/2 wave
transmission line does NOT produce the appropriate current phasing ( I
assume you are looking for a broadside pattern here?) You'll need to
adjust the lengths of the transmission lines while looking at the
phase of the current in the middle segment of each wire, to start
with...

Running your model, I get the following currents for segments 6, 17,
and 28 (the mid point of each wire) as
(.0039, phase -39), (..0033, phase 138), (.0031, phase -44)... No
wonder you are getting some beam tilt...

Also, you are driving this antenna from the end. Is it intended to be
above a ground plane?

The commercial antennas I have seen like this use a single wire to
connect the dipoles, typically wrapped around in some form at the
joint. The length of the hairpin is adjusted to get the phasing
right, and it is unlikely to be exactly 1/2 wavelength.
Received on Tue Apr 25 2000 - 05:08:39 EDT