Antenna Types (PDF)
New antenna technologies are being developed that allow an antenna to rapidly change its pattern in response to changes in direction of arrival of the received signal. These antennas and the supporting technology are called adaptive or "smart" antennas and may be used for the higher frequencyLMR bands in the future.

Wireless Networking Reference - Antennas / Range Boosting
Trying to get that little bit of extra range out of your wireless network? These articles may help.