To perform a TRL / LRM calibration:
Select TRL or LRM as the Cal Type at the Define Cal Settings dialog in the Cal and Measurement Wizard.
TRL (Thru, Reflect, Line) represents a family of calibration techniques that measure two transmission standards and one reflection standard to determine the 2-port 12-term error coefficients. For example, TRM (Thru, Reflect, Match), LRL (Line, Reflect, Line), LRM (Line, Reflect, Match) are all included in this family.
The traditional SOLT calibration measures one transmission standard (T) and three reflection standards (SOL) to determine the same error coefficients.
TRL calibration is extremely accurate, in some cases more accurate than an SOLT cal. However, very few calibration kits contain TRL standards. TRL calibration is most often performed when you require a high level of accuracy and do not have calibration standards in the same connector type as your DUT. This is usually the case when using test fixtures, or making on-wafer measurements with probes.
The DUT must be physically connected to the PLTS by some kind of transition network or fixture. Therefore, in some cases you must fabricate and characterize standards in the same media type as your DUT configuration. It is easier to manufacture and characterize three TRL standards than the four SOLT standards. A limitation for TRL cal with broad frequency coverage is the requirement for multiple LINE standards. For example, a span from 2 GHz to 26 GHz requires two line standards. Also, for lower frequencies, the LINE standard can be too long for practical use.
Keysight Technologies offers two cal kits that include the required standards to perform a TRL calibration: 85050C (APC 7mm) and 85052C (3.5mm). Both kits include the traditional Short, Open, and Load standards. (The Thru standard, not actually supplied, assumes a zero-length Thru). In addition, the kits include an airline which is used as the LINE standard. To use the airline, the kits include an airline body, center conductor, and insertion/extraction tools.
These standards must be defined in your TRL cal kit:
THRU
The THRU standard can be either a zero-length (also known as Flush THRU) or non-zero length. However, a zero-length THRU is more accurate because it has zero loss and no characteristic impedance. Learn more about zero-length THRU.
The THRU standard cannot be the same electrical length as the LINE standard.
If the insertion phase and electrical length are well-defined, the THRU standard is used to set the reference plane.
REFLECT
The REFLECT standard can be anything with a high reflection, as long as it is the same when connected to all ports.
The actual magnitude of the reflection need not be known.
The phase of the reflection standard must be known within 1/4 wavelength.
LINE
The LINE standard establishes the reference impedance for the measurement after the calibration is completed. TRL calibration is limited by the following restrictions of the LINE standard:
Limited to 4 Lines.
Must be of the same impedance as the THRU standard.
The electrical length need only be specified within 1/4 wavelength.
Cannot be the same length as the THRU standard.
Must be an appropriate electrical length for the frequency range: at each frequency, the phase difference between the THRU and the LINE should be greater than 20 degrees and less than 160 degrees. This means in practice that a single LINE standard is only usable over an 8:1 frequency range (Frequency Span / Start Frequency). Therefore, for broad frequency coverage, multiple lines are required.
At low frequencies, the LINE standard can be too long for practical use. Two 50-ohm terminations can be used in place of a long LINE standard at low frequencies.