Quadrifilar helicoidal antenna - Introduction - John Coppens

Design and construction of quadrifilar helicoidal antennas

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One of the two QFH antennas on NOAA-17 (Photo courtesy and (c) Lockheed Martin The quadrifilar helicoidal antenna - quite a mouthful - is easy to construct (even though it does look complicated), and the results are excellent. In contrast with the omnipresent turnstile antenna (two crossed dipoles with a reflector) the circularity is almost perfect in any direction. I've also received quite a few reports from people who built the antenna using the data from this page, who were very satisfied.

In it's original form, the relation between diameter and height is 0.44, but decreasing this relation slightly, a still better coverage of for satellites near the horizon is obtained. In literature and on the web, extreme versions can be found.

If the left column of this page (under 'Pictures') are links to pictures of several versions built by me and sent to me by several happy readers. The first link shows images generated by POV-ray.

On using the QFH for WiFi

Regularly I get questions similar to the one which follows:

Regularly I get questions similar to the one which follows:

Hi, your page is very interesting. I'm interested in an omnidirectional antena with circular polarization on 2.4 GHz, but I'm not sure if you have seen any successful tests using the QFH for 2.4 GHz. According to the calculator, I get an antenna which is slightly over 4.8 cm in height. Could you tell me the gain which would have this antenna? Would it be useful for a hot spot?

Alfred... There is no such thing as gain in an antenna. This is one of the most difficult things to teach my students. This term was established many years ago, probably for commercial reasons...

The correct term is directivity - i.e., the capacity of antenna to direct the available power into one preferred direction. This looks as a gain in the correct direction, but the power was 'stolen' from elsewhere.

mide Product Page

The QFH is an excellent antenna for satellites, as it receives from 'the entire northen hemisphere', from horizon to horizon, with all the sky in between. Such an antenna cannot have any significant 'gain', as it doesn't have directivity. Such an antenna is not useful for hot spots, as you probably won't have any clients 'in the sky'.

Moreover, your clients, except if you give them new, circularly polarizaed antennas, will probably be using vertical antennas from their laptops or notebooks. This means an extra loss of 3 dB because of the polarization.

I'll put this text on the page, as it seems to be a regular issue.

Greetings,
John

Bibliography on quadrifilar antennas

(c) John Coppens ON6JC/LW3HAZ

 # Model Frequency Bandwidth Gain Download ENQ 1. QHA- - MHz 1.1 - 1.3 GHz 2 dBic 2. QHA- - MHz -MHz 2 dBic 3. QHA- -MHz 1.2 - 1.6 GHz 2 dBi 4. QHA- - MHz 1.3 - 1.4 GHz 2dBi 5. QHA-150 135-175MHz 20 MHz 3 dBic 6. QHA- - MHz 1.4 - 1.7 GHz 2 dBic 7. QHA- - MHz 1.50 - 1.62 Ghz 2 dBic 8. QHA- - MHz 1.7 - 2.0 GHz 2 dBic 9. QHA- - MHz 1.7-2.6 GHz. 2 dBic 10. QHA- - MHz 2.0 - 2.3 GHz 2 dBic 11. QHA- - MHz 2.3 - 2.6 GHz 2 dBic 12. QHA- - MHz 2.6 - 3.0 GHz 2 dBic 13. QHA- -MHz 3.0 - 4.0 GHz 2 dBic 14. QHA-350 300-400MHz 40 MHz 3 dBic 15. QHA- -MHz 4.0 - 5.0 GHz 2 dBic 16. QHA-450 400-512MHz 70 MHz 3 dBic 17. QHA- - MHz 4.8 - 5.4 GHz 2 dBic 18. QHA- - MHz 5.0 - 6.0 GHz 2 dBic 19. QHA- - MHz 5.4 - 5.8 GHz 2 dBic 20. QHA-850 700-MHz 700 - MHz 3 dBic

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