On Sat, 01 Mar 2014 23:13:56 -0800, Jeff Liebermann wrote:

The 3dB difference in gains between the two bands is pure coincidence.
It can be anything.

OK. Maybe I'm mistaken.

In "my" experience, when I buy, say, an 18 inch dish reflector
for a WiFi radio, there always seems to be a 3dB gain in the 5GHz
specifications as compared to the 2.4GHz specifications for
the same power setting of the radio.

I had thought that 3dB doubling of power was due to the inherent
physics behind doubling the frequency from 2.4 to 5 GHz.