Meaning
Systematic error removal in vector network analyzer measurements relies on a sequence of known reference standards. This procedure, known as SOLT calibration, utilizes short, open, load, and through connections to define the measurement reference plane. It eliminates the phase shift, attenuation, and reflection errors introduced by test cables and fixtures.
Calibration Standard
High-precision physical devices with known electrical characteristics are connected to the test ports in sequence. For a successful SOLT calibration, the short standard provides total reflection with a hundred and eighty degree phase shift, while the open standard provides total reflection with zero phase shift. The load standard matches the characteristic impedance of the system to absorb all energy, and the through standard provides a direct path between ports.
Comparing the measured responses of these standards to their mathematical models allows the analyzer to calculate correction coefficients.
Error Correction
Twelve-term error models are calculated from the measurement of the four standards. Once SOLT calibration is complete, the network analyzer subtracts these systematic errors from subsequent measurements of the device under test. This subtraction ensures that the measured scattering parameters reflect only the performance of the device, not the influence of the cables.
Coaxial Measurement
Vector measurements of RF devices are highly sensitive to temperature drift and cable movement. When executing SOLT calibration, the operator must avoid bending the cables to prevent phase errors. The calibration remains valid only for the specific frequency range and port configurations selected during the setup.
