HP 8753D, User Manual, Page: 352 / 678

TRL*/LRM* Calibration
The HP 8753D RF network analyzer has the capability of making calibrations using the \TRL"
(thru-reect-line) method. This section contains information on the following subjects:
Why Use TRL Calibration?
TRL T erminology
How TRL*/LRM* Calibration W orks
Improving Raw Source Match and Load Match F or 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 specic
measurement environment, such as a transistor test xture 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 xture . Calibration
for a xtured measurement in microstrip presents additional diculties .
A calibration at the coaxial ports of the network analyzer removes the eects of the network
analyzer and any cables or adapters before the xture; however , the eects of the xture itself
are not accounted for . An in-xture calibration is preferable , but high-quality Short-Open-Load-
Thru (SOL T) standards are not 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 dicult to
produce over a broad frequency range . The Thru-Reect-Line (TRL) 2-port calibration is an
alternative to the traditional SOL T Full 2-port calibration technique that utilizes simpler , more
convenient standards for device measurements in the microstrip environment.
F or coaxial, waveguide and other environments where high-quality impedance standards are
readily available , the traditional short, open, load, thru (SOL T) method provides the most
accurate results since all of the signicant systematic errors are reduced. This method is
implemented in the form of the S
11
1-port, S
22
1-port, and full 2-port calibration selections .
In all measurement environments , the user 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 T erminology
Notice that the letters TRL, LRL, LRM, etc . are often interchanged, depending on the
standards used. F or example , \LRL" indicates that two lines and a reect standard are used;
\TRM" indicates that a thru, reection and match standards are used. All of these refer to the
same basic method.
Application and Operation Concepts 6-85