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?