Re: NEC-LIST:helical ant. modeling

Been published in:
IEEE transactions on antennas and propagation, May 1975, pg 392-397
You may find it at the university library.

Cornel

John Thompson wrote:

> Can someone give me a good source for this paper by Kilgus?
>
> Thanks!
>
> John N. Thompson
> Signal Engineering, Inc.
> 6370 Lusk Blvd., Suite F206
> San Diego, California 92121
> U.S.A.
> Tel: (858) 552-8131
> Fax: (858) 552-1429
>
> -----Original Message-----
> From: Cornel Gazdaru [mailto:cornel_gazdaru_at_botcorp.com]
> Sent: Saturday, October 06, 2001 2:07 PM
> To: nec-list_at_gweep.ca
> Cc: ghagn_at_erols.com
> Subject: Re: NEC-LIST:helical ant. modeling
>
> Thank you George,
>
> That is exactly what we are doing.
> We started with the Kilgus paper and build some prototypes that worked very
> well.
> Now we we plan to simplify the manufacturing aspect and look into a few
> variants,
> i.e. feed from the bottom and not from the top and open arms instead of the
> "closed loops". First results seem to suggest that it will work..
> All our work so far was based on copper wires, we want to replace with
> printed
> strip on a rolled tube. That is why I was looking at a way of modelling the
> strip.
> The general consensus suggests that a wire diameter 1/4 of the strip width
> should
> be a good approximation.
>
> Cornel
>
> "ghagn_at_erols.com" wrote:
>
> > All:
> >
> > Several years ago, I had a commercial client (Orbital Sciences' ORBCOMM)
> for
> > the design and prototype development and testing of an antenna for use in
> the
> > little LEO satellite band at 150 MHz. The best structure to satisfy all of
> the
> > requirements was a quad helix. I modeled it with NEC-3 (and then NEC-4)
> and
> > had good agreement with the measurements (done in anechoic chambers
> developed
> > for stealth work) and the NEC predictions--both patterns and impedance vs
> > frequency. The antenna designed is now in orbit! It was a real challenge,
> and
> > the SRI team I pulled together did a fantastic job of the almost
> impossible in
> > the trade-offs of weight budget, coverage, axial ratio, etc. Some of the
> > history of ORBCOM is available in the book, "Silicon Sky."
> >
> > The bottom line is that NEC accurately predicted the measured performance,
> and
> > was invaluable as a design tool.
> >
> > We used the classical paper by Kilgus to get us into the "zone" for good
> > performance. Kilgus was hired by ORBCOMM to come and give them a tutorial
> on
> > the quad helix. SRI had proven that the design, used for the first two
> birds
> > launched, would never meet the spec set down by ORBCOMM. That was a
> > disappintment to the management of ORBCOMM, since they were on their 3rd
> > antenna contractor prior to hiring me and my guys! But SRI designed the
> > antennas for the constellation that is now in orbit, and those antennas
> met
> > the spec. It was a satisfying project.
> >
> > So check out Kilgus' paper for some guidance on getting into the "zone",
> or
> > sweet spot, on the initial design. He did some great work! And trust NEC,
> but
> > verify (as Reagan said), with measurements.
> >
> > Hope this helps.
> >
> > George
> >
> > Original Message:
> > -----------------
> > From: Ian Roberts ITR_at_nanoteq.com
> > Date: Thu, 4 Oct 2001 17:02:49 +0200
> > To: ccc_at_space.mit.edu, nec-list_at_gweep.ca
> > Subject: RE: NEC-LIST:helical ant. modeling
> >
> > Hi Chuck,
> >
> > At 9:29 AM +0200 10/4/01, Ian Roberts wrote:
> > >My hands-on with a 22 turn helical at 435 MHz highlighted two aspects:
> > >Helicals suffer severe gain saturation if constant radius/constant
> spacing
> > >is applied....
> > >The workaround I applied was to group turns of this helical into 10 at
> 1.1
> > >circumference for maximum gain, 6 at 1.0 circum, and the rest at .95
> > >circumference while maintaining the same spacing....
> >
> > >?Never having tried to build a helical ant., I'm confused by this
> > >description. I'd like to understand:
> >
> > >Are you varying the radius of the helix while maintaining the axial
> > spacing of turns? Which end of the helix has smaller radius?
> >
> > Yes this is correct, the last turns at the feed end tend to define the
> > overall feed impedance of a helical. I don't think it can be reversed as
> one
> > would have a decreasing impedance characteristic as the wave approaches
> the
> > rear of the antenna (the feed end). It might be possible to feed the
> smaller
> > radius end and mount this againt the ground plane, but I don't know.
> > Progressively decreasing the element lambda/circumference as the wave
> > approaches the driven end would surely kill a yagi style antenna - it
> might
> > be OK in a helical.
> >
> > >Is a picture/drawing available?
> >
> > No, have a look at the illustration on the Web site mentioned previously.
> > There the approach regarding matching was different. The last turn was
> much
> > larger, as in a yagi, and served as a reflector.
> >
> > >Tnx -Chuck
> >
> > Cheers,
> > Ian.
> > --
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> > http://www.gweep.ca/mailman/listinfo.cgi/nec-list
> >
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