Terminating Unused Antenna Ports?

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Question:

What happens to the router or radio if you only terminate one antenna port with an antenna? I have been led to believe that this will cause (quite much) of the energy to be reflected – like an antenna with terrible VSWR and that this will harm the radio over time.

Answer:

Most of the latest consumer LTE and WiFi routers / modems have protection mechanisms that protect the radio when the antenna is faulty or disconnected.

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Theoretically it should not matter if the one port is left open or not. However, it remains best practice to terminate the port for the following reasons:

  1. The radio could be a rare model that does not have proper protection (like older models or models with marginally passed QA)
  2. Depending on the hardware, an open port could keep the port floating, thereby creating a higher risk of being affected during a power surge.
  3. It is possible that this floating scenario can develop other problems – remember the hardware is designed assuming both ports are connected – the protection mechanism is normally only meant for protection. I am not sure if all suppliers test their routers/modems with the one port floating.
  4. It is best not to depend on protection mechanisms and rather implement best practice – i.e. terminating the port.

So, even though it could be okay to leave the port open, we recommend to rather terminate the port, just to be extra sure.

How do you terminate the additional ports?

An impedance matching “termination stub” (e.g. 50 Ohm for most routers) should be a good option. As an alternate, I often suggest to customers to just use any cheap antenna (maybe the one that comes with the router).

E.g. if you connect a single external LPDA antenna on the roof of the building, there will be some benefit to using the second port, even if inside the building, for additional diversity – especially if the costs are negatable.

Or.. if you have a 4×4 MIMO router and want to use it with, for e.g. only one XPOL-2, then you can terminate the other two ports with the OMNI-510 indoors, or the antennas that came with the router.

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