Need to setup a wireless lan between 2 building 150m away .
Any1 can tell whay would be the best router or antenna if there are only 1 tree blocking the view of these 2 buildings ?
You need a wireless bridge (not AP or router) on each end. Some routers / APs can be configured to operate as bridges (but not all). Beyond the infrastructure device, you then have the distance problem. What is your budget?
I've had good luck using Linksys wap54gpe, but they've never stayed up for long term use. You can always additionally order external antennae, but I've never needed them with these radios in a similar situation to which you describe. I think they run around 400-450 each.
While we chose those radios because PoE was a requirement for us (it was a very interesting project), there may be cheaper solutions out there as well. I know there are also a lot more expensive ones. We also have a permanent wireless bridge set up using dual band 2.4/5.4 SMCs which works very well.