Re: Helical Antennas

I received this email thread from a friend. At the risk of injecting
myself in the middle of the discussion, you may want to check out
the NEC model and prototype of a 23 turn, 3 step taper and
non-screen reflector helix design on my webpage:

      http://www.webcom.com/af9y

Mike Cook, AF9Y

> Date: Fri, 9 Aug 1996 13:33:40 -0400 (EDT)
> From: Neil Fox <builder_at_cais.com>
> To: Feng Niu Research <niufeng_at_plhp002.comm.mot.com>
> Cc: BURKE_at_icaen.llnl.gov, JKB_at_arlvax.arl.psu.edu, nec-list_at_ee.ubc.ca,
> SooLiam Ooi-CSO005 <SooLiam_Ooi-CSO005_at_email.mot.com>
> Subject: Re: Helical Antennas

> Your comment is very reasonable - normal mode helical antennas would be
> better modeled by NEC. When the higher modes of the helix come into play
> (T1, T2 modes) for long helices, the so-called "axial mode" is poorly
> modeled. Results tend to be increasingly optimistic for increasingly long
> helices. I can not say how accurate normal mode modeling would be, but
> since the directivity is so low, I'd expect the error to be less than a
> dB at boresite.
>
> On Fri, 9 Aug 1996, Feng Niu Research wrote:
>
> > X-Mailer: Z-Mail (3.2.0 16aug94)
> > Mime-Version: 1.0
> > Content-Type: text/plain; charset=us-ascii
> >
> > I would like to hear more comments on this subject. I cannot see why
> > the NEC-like modeling does not apply to helical antennas at least in
> > the normal mode (small antennas, for example) where they act more like
> > short dipoles.
> >
> > My question is:
> >
> > Does NEC apply at least to some helical antennas, and any
> > benchmark solutions have been done to quantify how acurate the NEC solutions
> > are for helical antennas?
> >
> > Feng
> >
> > On Aug 8, 7:56, builder#064#cais.com%INTERNET_at_email.mot.com wrote:
> > > Subject: Re: Helical Antennas
> > > My masters thesis was a study of helical antennas, and the building of a
> > > prototype helical array (hooray for me ...). I found that NEC was 100%
> > > unreliable for helical antennas in both the so-called axial and normal
> > > modes. It has to do with the fact that the helical antenna acts as a
> > > waveguide structure that does not lend itself to NEC-like modeling. Kraus
> > > and some others tried to characterize helical antenna gain using NEC-like
> > > methods (actually closed form solutions), resulting in gross
> > > overestimates. Some really good work was done by Aerospace Corp (King and
> > > Wong) in the 1970's (?).
> > >
> > > On Wed, 7 Aug 1996, Mike Slater wrote:
> > >
> > > > I would appreciate any information pertaining to
> > > > helical antenna performance using NEC. I have heard
> > > > some remarks about NEC not being reliable, however,
> > > > I have not been able to find any literature,
> > > > results etc. that support or refute these claims.
> > > > If anyone has any info/suggestions/links I would
> > > > greatly appreciate any information.
> > > >
> > > > Thank you.
> > > >
> > > >
> > > > Mike Slater
> > > > mike_s_at_ece.concordia.ca
> > > > mike_s_at_pils.com
> > > >
> > > >
> > >
> > >
> > >-- End of excerpt from builder#064#cais.com%INTERNET_at_email.mot.com
> >
> >
> >
> > --
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>

de Mike, AF9Y
http://www.webcom.com/af9y
Work: mwcook_at_itt.com
Home: mwcook_at_cris.com
Received on Sat Aug 10 1996 - 02:15:00 EDT