1. A method for characterizing a first interface device and a second interface device using a vector network analyzer (VNA), the first and second interface devices useful for connecting a two-port device under test (DUT) to the VNA, the method comprising the steps of: (a) performing a two-port calibration at each of a first outer reference plane and a second outer reference plane; (b) performing a two-port calibration at each of a first inner reference plane and a second inner reference plane; and (c) determining a set of scattering-parameters for each of the first and second interface devices based on results of the calibrations performed at step (a) and results of the calibrations performed at step (b), each set of scattering-parameters characterizing a respective one of the first and second interface devices.