Since the output from the radio transceiver itself is a balanced signal pair, a balun is needed to transform into a 50Ohm single ended signal fed to the SMA connector. Johanson Technology provides two pin compatible baluns for the AT86RF230, AT86RF231 and AT86RF212:
2450FB15L0001: 2.45 GHz filter balun optimized for AT86RF230 and AT86RF231.
0896FB15A0100: Sub gigahertz filter balun combination optimized for AT86RF212.