A one-port calibration can measure and minimize three systematic error terms (directivity, source match, and reflection tracking) from reflection measurements. Three known calibration standards must be measured, such as a Short, Open, and a Load (the load value is usually the same as the characteristic impedance of the test system, generally either 50 or 75 ohm). One-port calibration makes it possible to derive the DUT's actual reflection S-parameters.
One-port calibration methods
(SOL) Short-Open-Load calibration - Response calibration for measuring VSWR/Return Loss.
(SSL) Short-Short-Load calibration - Calibration for measuring VSWR/Return Loss in waveguide applications
Why use Sliding Loads? When performing a SOL, SOLT, or SSLT (waveguide) calibration the impedance standard is the Load. At frequencies above 2 GHz (4 GHz for 2.4mm) sliding loads are more accurate impedance standards. Therefore Sliding Loads will provide a better calibration at higher frequencies. (Reduced directivity error)
Two-port error correction yields the most complete calibration because it accounts for the three major sources of systematic error addressed by one-port calibration at both ports of a twoport DUT. Traditional full two-port calibrations utilize three impedance standards and one transmission standard to define the calibrated reference plane. These standards, typically a Short, Open, Load, and Thru, make up the SOLT calibration kit. The most common Thru used is the test ports connected directly together.
Two-Port full calibration methods
(SOLT) Short-Open-Load-Thru - Full two-port calibration for performing forward and reverse transmission and reflections measurements.
(SSLT) Short-Short-Load-Thru - Full two-port calibration for performing forward and reverse transmission and reflections measurements.
(TRL) Thru-Reflect-Line - Full two-port calibration for performing forward and reverse transmission and reflections measurements.
TRL corrects the same error terms as a SOLT calibration, although it uses different calibration standards. Other variations of TRL are Line-Reflect-Line (LRL), (LRM) based on Line-Reflect-Match (load) calibration standards or Thru- Reflect-Match (TRM) calibration standards. In non-coaxial applications such as waveguide, TRL usually achieves better source match and load match corrections than SOLT. While not as commonly used, coaxial TRL can also provide more accuracy than SOLT, but only if very-high quality coaxial transmission lines (such as beadless airlines) are used.