I am planning a outdoor Mesh-Network in 802.11a. It will consist of about 10 nodes on roofes of buildings with a distance of about 100-300m and I think about to use RouterBoard devices. Because it shall be a backbone network, there is need of full throughput, eg 54MBit/s. Therefor I want to use devices with several 802.11a interfaces, mostly 2-3. Then I want to set up dedicated connections between only 2 devices in one channel, so that there is maximum throughput. But I still don't know what antennas I should use. Because the network consists of several point-to-point links in different channels, it seems to use directional antennas. But how much are directional antennas for 802.11a, and do I really need them, or can I use "simple" omni ones?