Quadrifilar Antenna Gain achievable

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...

(Surprisingly) it would seem the answer to your question is YES!

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: http://www.w1npp.org/ARES/REFLEC~1/R...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 http://mtt.ieee.cz/studentska-soutez...mova_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 :)

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