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Operating Concepts
TRL*/LRM* Calibration (ES Models Only)
TRL*/LRM* Calibration (ES Models Only)
The network analyzer has the capability of making calibrations using the "TRL" (thru-reflect-line) method.
This section contains information on the following subjects:
• Why Use TRL Calibration?
•TRL Terminology
• How TRL*/LRM* Calibration Works
• Improving Raw Source Match and Load Match for TRL*/LRM* Calibration
• The TRL Calibration Procedure
— Requirements for TRL Standards
—TRL Options
Why Use TRL Calibration?
This method is convenient in that calibration standards can be fabricated for a specific measurement
environment, such as a transistor test fixture or microstrip. Microstrip devices in the form of chips, MMIC's,
packaged transistors, or beam-lead diodes cannot be connected directly to the coaxial ports of the analyzer.
The device under test (DUT) must be physically connected to the network analyzer by some kind of
transition network or fixture. Calibration for a fixtured measurement in microstrip presents additional
difficulties.
A calibration at the coaxial ports of the network analyzer removes the effects of the network analyzer and
any cables or adapters before the fixture; however, the effects of the fixture itself are not accounted for. An
in-fixture calibration is preferable, but high-quality short-open-load- thru (SOLT) standards may not be
readily available to allow a conventional full 2-port calibration of the system at the desired measurement
plane of the device. In microstrip, a short circuit is inductive, an open circuit radiates energy, and a
high-quality purely resistive load is difficult to produce over a broad frequency range. The Thru-Reflect-Line
(TRL) 2-port calibration is an alternative to the traditional SOLT Full 2-port calibration technique that utilizes
simpler, more convenient standards for device measurements in the microstrip environment.
For coaxial, waveguide and other environments where high-quality impedance standards are readily
available, the traditional short, open, load, thru (SOLT) method provides the most accurate results since all of
the significant systematic errors are reduced. This method is implemented in the form of the S
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1-port, S
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1-port, and full 2-port calibration selections.
In all measurement environments, you must provide calibration standards for the desired calibration to be
performed. The advantage of TRL is that only three standards need to be characterized as opposed to 4 in
the traditional open, short, load, and thru full 2-port calibrations. Further, the requirements for characterizing
the T, R, and L standards are less stringent and these standards are more easily fabricated.
TRL Terminology
Notice that the letters TRL, LRL, LRM, etc. are often interchanged, depending on the standards used. For
example, "LRL" indicates that two lines and a reflect standard are used; "TRM" indicates that a thru,
reflection and match standards are used. All of these refer to the same basic method.
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