[time-nuts] Quadrifilar Helix Antenna

[David Kirkby]

On 9 June 2012 15:53, Azelio Boriani <azelio.boriani at screen.it> wrote:
> Of course one of the most challenging part of the EM simulators is
> preparing the correct model of the structure you want to simulate.

Agreed.


> Unfortunately (for me) I'm mostly a try-it guy rather than simulate-it so I
> prefer to build and try with test equipment. My first QFH was too high in
> frequency (GLONASS-ready?) so I have to build another one.

But there are obvious advantages to being able to model something
first, especially in a case like this, where there is nothing I see to
indicate this is optimised in any way. So it might be possible to
improve on it. Experimentially determing if something is on frequency,
and if not making another is not that hard, but knowing how various
changes might affect the radiation pattern is less easy to predict.

If you can accurately model the one you built, you might get some idea
about other changes that could be made. I doubt the EM simulation
tools will get the frequency spot on, but I find they give me insight
into the problem.

At this very minute I'm running a simulation of a 7 turn axial model
helix antenna with a view to determine if the use of steel would give
significantly poorer performance than copper. You would probably have
a hard-time measuring the differences, and its a lot cheaper to just
re-run a simulation than to build two of them and measure them.

Dave


>
> On Sat, Jun 9, 2012 at 4:11 PM, David Kirkby <david.kirkby at onetel.net>wrote:
>
>> On 8 June 2012 09:31, Raj <vu2zap at gmail.com> wrote:
>> >
>> > I came across this article. I dont understand Italian!
>> >  From RadioKit Elettronica 2003-03
>> >
>> > https://dl.dropbox.com/u/10377704/IV3QBN%20QuadHelix.pdf
>> >
>> > Cheers
>> >
>> > --
>> > Raj, VU2ZAP
>> > Bangalore, India.
>>
>> I'd be interesting in trying to see some simulations of this in a full
>> wave 3D electromagnetic simulator like HFSS from Ansys, FEKO, EMpro
>> from Agilent etc. I currently have a trial license for Agilent's
>> EMpro, but don't feel confident in trying this antenna. I would have
>> been a bit happier using HFSS, but don't have a license for it.
>>
>> Maybe one of the much cheaper NEC based programs coud do this, though
>> I'm not so sure I'd trust the results, whereas I would from HFSS.
>>
>> HFSS (which costs a small fortune), comes with a free antenna design
>> kit. That is able to design a Quadrifilar Helix Antenna, but needs a
>> ground plane, so has a very different radiation pattern to this.
>>
>> Dave
>>
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