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#### Guruditya Sinha

##### Junior Member level 2
Hi,
My query is on quadrifilar helical antenna for the S-Band frequencies. Currently I'm trying to do hand-calculations on the design.

Q. Whether a gain of > -2dBi is achievable at the +/-125 degree from the antenna normal? What I do find is that a lot of the antennas off the shelf have the gain of <-6dBi near the antenna normal. Can anyone suggest a methods/references on improving the gain at the +/-125 degree point?
The antenna gain at the antenna normal can be negotiable for my design case.

Thanks...

The radiation pattern of the quadrifilar helix (QFH) is a primarily a function of three parameters:
1. The length of the radiating loops,
2. The diameter of the antenna, and
3. The number of twists made by the loops over the antenna's length.

A chap by the name of M.W. Maxwell created a catalogue of QFH radiation patterns vs these parameters in the late 70's. He describes the catalogue (and the antenna) here: www.w1npp.org/ARES/REFLEC~1/REFLEC~1/AP3F3F~0.PDF ... but I can't find it with a casual Google search [if you find it, please post back a link!]

A little poking around turned up a Czech student's thesis https://mtt.ieee.cz/studentska-soutez/soutez2013/vafek_diplomova_prace.pdf which shows (in Figure 23) a helix with diameter = 0.75 wavelengths has significant radiation at angles ~+/-110 degrees. I dare say there's a solution out there

Points: 2

### Vaishnavi Ramseh

Points: 2
Thanks thylacine1975.

I have an additional query on this.
If I am to maintain axial ratio below 3dB and also maintain gain better than -2dBi for a +/-125 degrees QFH antenna, How do I achieve this?

I seem to be perplexed with this problem.

Hi thylacine1975,

I'm working on QFH currently. My query is that whether the axial ratio (<3dB) bandwidth of minimum 20MHz can be achieved over a beamwidth of 210 degrees at S Band frequencies ??

And I kindly request you to post the English version of Czech student thesis which can help me massively in sorting out my problem.

Thanks..

I find it surprising that there is not more information on the quad helix. I have achieved positive gain with several versions but have not touched one in years.

Look up the article by Kilgus. You can find some additional information by searching on Volutes. I have no idea why that name was chosen.

Azulykit

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