Introduction

POYNTING offer a range of underground/tunnel antennas, namely the HELI and miniHELI series. Branded as MinePoynt antennas, these antennas are suited for various types of tunnels, including mining, tunnelling, automotive tunnels, shipping tunnels, etc. These antennas offer solutions where the next level of ‘Industrial’ grade communication system is required, to offer more reliable and more stable networks for safety purposes, telemetry, automation or just general communications underground.

Why Circular Polarisation for tunnels? 

When using ‘normal’ linear antennas in open air environments, it is important to have the transmit and receive antennas fully aligned to achieve the maximum signal transfer – I.e. both antennas should either be vertically aligned or horizontally aligned. When a linear antenna is used in a tunnel (the red wave in the example), this causes the RF wave to be reflected from the non-linear (rounded/angular) surfaces, resulting in the signal to rotate unpredictably down a tunnel. The received wave (the green wave in the example) is likely to be received at the wrong polarisation, reducing the efficiency of the system.

Why Circular Polarisation for tunnels? 

When using ‘normal’ linear antennas in open air environments, it is important to have the transmit and receive antennas fully aligned to achieve the maximum signal transfer – I.e. both antennas should either be vertically aligned or horizontally aligned. When a linear antenna is used in a tunnel (the red wave in the example), this causes the RF wave to be reflected from the non-linear (rounded/angular) surfaces, resulting in the signal to rotate unpredictably down a tunnel. The received wave (the green wave in the example) is likely to be received at the wrong polarisation, reducing the efficiency of the system.

When using a circular polarised antennas in tunnel communications systems, e.g. with an Access Point (AP) or Mesh Node, it will receive a combination of LHC & RHC reflected signals. To enhance the RF link performance for mission critical Industrial Internet of Things (IIoT) networks, it is advised to deploy both LHC and RHC antennas to benefit from the various mirrored waves.

Some of our MinePoynt and MiniHELI antennas are available in both LHC and RHC polarisation for dual-band Wi-Fi, Wi-Fi-6 (802.11ax), LTE & 5G cellular applications. The benefit of using both RHC & LHC polarised antennas with a MIMO Access Point (AP) or Mesh Node is that it provides better decorrelation between the various propagated signals, resulting in better diversity and MIMO performance in these difficult RF environments. It will result in an improvement in reception quality and data throughput. Making use of both LHC and RHC polarised antennas with ‘Beam Forming’ routers also enhances the router’s signal mixing/combining processes from the different received signal streams, especially routers that dynamically assign packets to all the streams independently.

For Single Input Single Output (SISO) applications it is necessary to use only one of the polarisations, so which one needs to be chosen? In straight commercial tunnels where the signal is propagated with Line of Sight (LoS), such as car and train tunnels, it is necessary to match the circular polarised antennas, i.e. RHC must be used with a RHC antenna or vice versa (LHC with a LHC antenna).