It makes no sense to me why you would want to design your own radio system for making a wireless network connection when you can purchase 802.11 wireless networking devices and antennas as mentioned in the very first response. It's certainly not going to be an easy project if you try to build your own. For one thing, surely you are going to get a lot of errors in transmission with a homemade system at such a high distance... how well will the wired 10baseT devices be able to handle these errors, when normally they would have very low error rates over a hard wired connection? existing wireless devices would already have such problems solved for you...