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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 no t b e r ea d i ly 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 S11 1-port, S22 1-port, and full 2-port calibratio n
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.