Yes you need a AP, the best i can suggest is a outdoor unit that can be a AP or wireless client, antenna is built in and its outdoor rated up to 7 km, try this
Long Range Wireless LAN system---Zigwire
Product Name:ASU-24005g
Product Class:Long Range Wireless LAN system
Features: ASU-24005g 2.4GHz, 802.11g , Fighter Outdoor Long Range WLAN

Details...
Hope this helps, if not email them and they will help you www.zigwire.net