RE: NEC-LIST: phasing networks on collinear arrays

If you are using NEC, model the coil as a helix using the GH card.
Make sure to model the form factor of the coil as closely as possible.
You should use at least 4 segments per turn. At the junctions to
straight wire segments, be sure to maintain the segment length and
wire diameter that you used in the coil. You can then gradually taper
segment length from one wire to another as you get away from the
junction to something more appropriate for a straight wire. Keep
segment length ratio less than 5 between wires at a junction. For the
helix, adjacent turns will couple to one another just as they do in
real life, and you will get the expected phase shift. Check the phase
of the current distributions if you want to verify this.

John Yorko

Paul Gili asked:
>
> How does one model the inductive- looking section commonly used on a
> cellular phone type antenna? It is my understanding that this
> circuit element provides a current reversal to obtain in-phase
> currents on adjacent half-wave sections of the antenna wire when
> driven at one end against a ground plane. Without the 180 degree
> phase shift, the half waves would be in phase opposition thereby
> causing a multi-lobed pattern. A simple series inductance would not
> seem to perform this function.
Received on Thu Nov 26 1998 - 10:37:50 EST