TRL Calibration

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.

See other Calibration Topics

Why Perform a TRL Cal?

TRL calibration is extremely accurate, in most cases more accurate than an SOLT cal. However, very few calibration kits contain TRL standards. TRL Cal 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. Therefore, in some cases you must construct 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.

Another advantage of TRL calibration is that the TRL standards need not be defined as completely and accurately as the SOLT standards. While SOLT standards are completely characterized and stored as the standard definition, TRL standards are modeled, and not completely characterized. However, TRL cal accuracy is directly proportional to the quality and repeatability of the TRL standards. Physical discontinuities, such as bends in the transmission lines and beads in coaxial structures, will degrade the TRL calibration. The connectors must be clean and allow repeatable connections.

To learn more about Cal Standard requirements, see Cal Standards Used in TRL.

The TRL Cal Process

Although TRL can be performed using the Cal Wizard Unguided Cal selection, the following process uses the easier SmartCal selection. Both selections require that you already have TRL calibration standards defined and included in a PNA cal kit.

  1. Preset the PNA

  2. Set up a measurement and the desired stimulus settings.

  3. Click Calibration / Calibration Wizard

  4. Click SmartCal (Guided Cal).

  5. Select the DUT connectors and Cal Kit for each port. The LOWEST port number of each port pair MUST include TRL standards. TRL appears as the Cal Method.

  6. Check Modify Cal, Next, then View/Modify to change default TRL options if necessary.

  7. Follow the prompts to complete the calibration.

  8. Check the accuracy of the calibration

TRL Cal Kits

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. The APC 7 kit includes an adapter to connect the airline to the APC connector.

Cal Standards Used in TRL

These standards must be defined in your TRL cal kit:


Note: All THRU calibration methods are supported in a TRL Cal EXCEPT Unknown Thru.



The LINE and THRU standards establish the reference impedance for the measurement after the calibration is completed.  TRL calibration is limited by the following restrictions of the LINE standard:

Note: The TRL LINE standard must have a delay that is greater than 0 (zero) ps. Otherwise, calibration correction calculations will contain unpredictable results.


If the LINE standard of appropriate length or loss cannot be fabricated, a MATCH standard may be used instead of the LINE.

See Also

TRL on a 4-port PNA-L and ALL PNA Models with an External Test Set  

Beginning with the PNA code revision 5.25, TRL CAN be performed on a 4-port PNA-L and ALL PNA Models with an External Test Set enabled. Previously, a TRL calibration required a PNA with a reference receiver for each test port. With the new TRL method, a Delta Match Calibration is first performed and applied.

Note: See Delta Match Calibration to learn which models require this.

The accuracy of this TRL cal greatly depends on the accuracy of the Delta Match Calibration. With an accurate Delta Match Calibration, the difference in accuracy between a traditional TRL cal and this TRL cal is negligible.

How to Perform a TRL Cal in these cases

  1. Click Calibration, Cal Wizard.

  2. Select a TRL cal kit for the ports to be calibrated.

  3. During the calibration, the Cal Wizard prompts you for a valid Delta Match Cal.

Last modified:


Fixed models for GDM cal.


added line std note


Slightly modified for cals on apps and added link to TRL Options.


Added App Note link


with Ext Test Set