60 GHz Technology

[Robert E. Seastrom]

Quoting the article:

   Attenuation is also aggravated by H2O absorption. Water (mainly oxygen
   molecules) in the atmosphere absorbs radio waves since the signal
   wavelength is about the size of the oxygen molecules. This absorption
   effect peaks at 60 GHz, making this a real issue for longer-range
   applications.

60 GHz = 5mm wavelength.  Them's some mighty big oxygen molecules.  :-)

-r