Hello,
I am sorry but according to what I can see in datasheets, there is no option for the 1100 series to be connected to an external antenna. The 1100 series were equipped with a built-in dipole antennas only, and no connector for an external antenna is available on the radio module. It appears that there is no official way to connect an external antenna to the 1100 series access point.
I am sorry to disappoint you.
Best regards,
Peter