In article ,
"john" wrote:

Wireless routers come with small antennas. There are high gain,
non-directional antennas you can buy , like this:
http://www.amazon.com/Linksys-High-A.../dp/B0002F3E9M

If the antenna is directional, I can understand how it could achieve high
gain (by concentrating the radio wave in one direction). But it is
non-directional, so where does the extra gain come from?

The gain comes from taking the Spherical shape of a Point Source RF
Emitter, and squashing it Flatter. Think of a round balloon. What
happens if you put it on a table and push down on the top. it gets
fatter. Ok?