External antennas are the best option to extend the coverage area. Integrated antennas cannot be used to cover great distances and therefore ii is not recommended.
Use the Outdoor Bridge calculation utility to decide on the external antenna to be used. For more information on calculation utility, refer to Outdoor Bridge Range Calculation Utility.
Note: If the distance between the endpoints is long, the integrated antennas cannot be used. So it is a good practice to determine the range of the endpoints before deploying. Then decide on the antenna to be used.
For more information, refer to these topics:
Interference issues ( EMI / RF issues)