11.3 Covering Tunnels with Antennas

For a short tunnel of a few hundred meters where you have line of sight from one end to the other the preferred coverage system in a tunnel will often be yagi antennas at the end of the tunnel beaming through the tunnel as well as covering the HO zone to the tunnel. This is a fast and relatively inexpensive solution (See Section 11.11.4 & Figure 11.28). Often these solutions will be operating on the nearby macro cell via a repeater system and thus not even require a dedicated base station.

Although antennas inside the tunnel, even for large tunnels, feeding sections of the tunnel to provide end to end coverage (as illustrated in Figure 11.5) are a viable solution there are some pitfalls that are to be avoided. Let us have a look on some of the common issues that one needs to consider carefully.

  • Mechanical issues; it is very important to ensure that the antennas are mechanically sturdy and are actually designed to be installed in the challenging environment of the tunnel. This will mean using antennas that are 100% enclosed in a plastic radome to protect them from dust and other mechanical issues.
  • Vibrations and wind load from passing traffic are not to be underestimated and special antennas that can be fixed to the wall in each end of the antenna radome are often to be preferred inside the tunnel.
  • Tunnel clearance profile (The kinetic envelope): you must make sure to stay clear of the ‘traffic profile’ of the tunnel – this is the defined zone ...

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