A directional antenna is an antenna which radiates greater power in one direction allowing for increased performance on transmit and receive and reduced interference from unwanted sources. It can also be made for either vertical, horizontal or circular polarisation
Directional antenna is a type used in wireless LAN which is primarily used to connect a wireless user (or Client Node) to an Access Point in a community wireless network, and are also used for dedicated point to point connections between Core Router Nodes.
The recommended frequency and gain for a directional antenna for a Client Node is 2.4Ghz with a gain generally between 19 and 25dbi with the higher gain being the better option but be sure EIRP is kept well within ACMA regulations.
The recommended frequency and gain for a directional antenna for a dedicated point to point connections between Core Router Nodes is 5.8Ghz with a gain generally between 26 and 30dbi but again please ensure EIRP is kept well within ACMA regulations.