I am working on a project that requires me to mount a WiFi antenna underneath a roof made of metal sheet. The antenna is mounted at a 2 m height, and the roof is just a few inches above the antenna.

I am using an omni-directional (dome shaped) antenna at the 5 GHz band. The proposed solution is to have a cut out on this metal sheet such that the antenna would still be able to transmit through it hence I was asked to provide the metal free zone required for my antenna.

Is this metal free zone related to the near field of the antenna? Or am I stupid. Please help


2 Answers 2


If you want the antenna to transmit through the sheet, the metal will need to be removed. For almost all metals, the skin dept at 2.4GHz is less than 0.1mm, and even lower for 5GHz. The skin depth is the amount of metal it would take to attenuate the signal roughly 1/3rd. If you want to transmit through the metal, it will need a metal free zone.

It might be easier to put an access point (or antenna from the same AP if it has that option, you can get extension cables for most antennas with minimal attenuation) on the other side.

  • \$\begingroup\$ Thanks for the answer, I am considering having a "window" cutout, but it seems that it will have an adverse impact instead. blog.antenova.com/… \$\endgroup\$
    – pokemon978
    Commented Jul 12, 2019 at 1:54
  • \$\begingroup\$ That blog is written for an enclosure, which is different from a room. \$\endgroup\$
    – Voltage Spike
    Commented Jul 12, 2019 at 18:34
  • \$\begingroup\$ Thanks for the reply. How do I calculate this metal free zone from the antenna specs? The only equation that came across my mind regarding the antenna is the near field equation. \$\endgroup\$
    – pokemon978
    Commented Jul 15, 2019 at 1:32

Yes if the metal is ferrous it can cause problems. I worked a long time ago on a project where they mounted aerials for telemetry on moving carts on the iron chassis. The transponder failed completely. The iron basically soaks up all your flux - acts as a near short circuit.


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