Keysight N9918AU-211 Base N9918A combination analyzer includes a cable and antenna analyzer. Option 210 provides transmission/reflection or S21 and S11 measurement capabilities, along with one-port and enhanced response calibrations. To obtain all four S-parameters - forward and reverse (S11, S21, S12, S22), and full 2-port calibration, Option 211 should be ordered. Full 2-port calibration is the most accurate calibration available with FieldFox network analyzers.brbrOption 211 also adds A/B and B/A measurement capabilities to the vector voltmeter mode, available as Option 308.brbrOption 210 is a prerequisite for Option 211. So you must order Option 210 if you want Option 211.brbr*This is the field-upgrade version. For factory-installed options, please see a sales representative for a customized unit.