Why Are Circular Polarised MinePoynt HELI Antennas Better For Tunnels?

Apr 25, 2019 | Frequently Asked Questions

Poynting has designed and patented their circular polarised MinePoynt “HELI” antenna, which was specifically developed for mining tunnels more than 20 years ago. This antenna was far ahead of its time, and the company has experienced exponential sales over the recent years. As this antenna is being implemented in more and more mines internationally, its reputation is becoming this antenna’s selling point – this is as a result of the antenna’s superior performance in this difficult environment.

Numerous customer tests in mines have been performed over the past years showing Poynting’s MinePoynt “HELI” antennas to achieve ranges 3x to 4x (and farther) those obtained with a linear polarised antenna of similar gain. Why is this? Why are circular polarised antennas, such as our HELI range, so much better in mining and other types of tunnels?

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The implementation of RF systems, such as WiFi, LTE, etc. in mine and other types of tunnels, quickly come to the realisation that exceptional measures need to be taken to compensate for the harsh RF environment. The implementation of normal linear antennas is not necessarily good enough. The RF propagation in these tunnels becomes complicated by:

  • The high RF reflective tunnel surfaces and scattering.
  • High clutter environments (Locomotives, hauling, machinery, etc.) which occupy and therefore obstruct the normal RF propagation path.
  • Narrow and confined spaces, where propagation is limited.
  • No Line of Sight (LOS) as the tunnels keep twisting and turning irregularly.
  • Irregular dimensions and shapes of the tunnels.

This is where circular polarised antennas, such as the Poynting MinePoynt “HELI” antenna thrives and overcomes the harsh mining tunnel environments. The key reasons for the circular polarised antenna, such as the Poynting HELI antenna, performing exceptionally better is due to the following aspects:

1. Linear polarisation rotates unpredictably down a tunnel

Linear polarisation rotates unpredictably down a tunnel, resulting in little or no signal for a linear antenna at certain points whereas circular polarisation contains all polarisations, therefore resulting in significantly more reliable links are maintained.

 

Looking at measurements detailed in an APNewsletter article, which were performed for different polarisations, one can see that a tunnel changes polarisation unpredictably. From this article: after a 100m or so, one measures roughly equal signal in vertical and horizontal polarisation regardless of whether a vertical or horizontal transmit antenna was used. If you use vertical polarisation you may completely lose communication at certain points because at that position only horizontal is available due to reflection, refraction, fading etc.

With circular polarisation, both (and in fact all polarisations) are transmitted and a much more stable signal is established down the tunnel.

2. No interference of First Reflections when using circular polarisation

The first reflection from tunnel walls cause NO interference for circular polarised RF waves, whereas linear polarisation experience significant interference from a reflected wave.

Linear polarisation changes phase upon the first reflection and causes a reflected wave from the side of the tunnel that interferes with the direct wave giving large signal variations with a change in distance.

Circular waves change from Right Hand Circular polarisation (RHC) to Left Hand Circular polarisation (LHC) upon reflection which means they do NOT interfere after the first reflection (only the second reflection may interfere with the original wave) and multipath interference is significantly reduced.

3. Linear polarisation propagation affected by tunnel dimensions, circular ‘adapts’ better.

Tunnel dimensions allow some linear polarised waves to propagate overall better than others at a specific tunnel dimension, however, mine tunnels do not have consistent dimensions and once again circular polarisation ensures the best signal regardless of tunnel dimension variations

Almost all tunnel measurements show either vertical or horizontal to propagate better depending on the specific tunnel dimensions – using circular means that regardless of which polarisation propagate better, the circular wave “contains all polarisations” so naturally “adapt” and ensure whichever one happens to propagate best gets to other side more effectively.

4. Circular polarisation more reliably propagates past obstacles & obstructions

Circular polarisation gets past obstructions in tunnels much more reliably because certain polarisations always propagate better than others around such obstructions

When obstacles (such as locomotives, hauling machinery, etc) are encountered in a tunnel, one once again finds that certain polarisations propagate better past these obstacles compared to others which once again makes circular more resilient and ensures the best possible propagation past such obstacle.

You are welcome to subscribe to the Poynting YouTube channel learn more about antenna principles. Have a look at this video where we explain antenna polarisation.

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