Antennas are passive devices that radiate radio frequency energy (RF). They do not create RF energy, but they do focus the energy in a specific area or direction, which increases the signal strength in that direction or area. This is specified as Gain in units of dBi. An antenna with 0dBi gain is one which radiates in all directions equally. An antenna with 12dBi gain, has a direction in which the signal is 12db stronger than in another direction.
Antenna links and infotainment for Wireless
WLAN Antenna Frequently Asked Questions http://www.telexwireless.com/wlanfaq.htm A very Commercial point of view.
Extending the range of your Airport base station: http://seattlewireless.net/index.cgi/AppleAirportMod
Build Your Own
The SEATTLE WIRELESS PROJECT has an interesting bit here http://www.seattlewireless.net/index.cgi/BuildingYagiAntennas Different materials for directional YAGI.
The Seattle Antenna How To http://www.seattlewireless.net/index.cgi/AntennaHowTo Again more EXCELLENT pics.
From Canberra, Australia Howto make a helical antenna. http://users.bigpond.net.au/jhecker/
Use a Surplus Primestar Dish as an IEEE 802.11 Wireless Networking Antenna http://www.wwc.edu/~frohro/Airport/Primestar/Primestar.html I just LOVE the soup can. Where's Andy Warhol when you need him?
Build your own antenna 4 different cheap ways! http://www.qsl.net/n9zia/wireless/ Really EXCELLENT!
[http://www.saunalahti.fi/~elepal/antenna2.html Waveguide] by Martti Palomaki
Calculators and Software
Homebrew Test Equipment And Software for the wireless Geek. http://www.gbonline.com/~multiplx/wireless/appendixF.html
The Wireless calculator. http://www.air.net.au This is a calculator for building Yagi antennas in the 2.4 Ghz range. Change length, wire wrap spacing or center freq. Very cool Look like the easiest to build.