Improving Raw Source Match And Load Match For Trl*/Lrm* Calibration - Agilent Technologies 8753ET User Manual

forward source match (E
reverse source match (E
SR
For a fixture, TRL* can eliminate the effects of the fixture's loss and length, but does not completely remove
the effects due to the mismatch of the fixture.
NOTE Because the TRL technique relies on the characteristic impedance of transmission lines, the
mathematically equivalent method LRM (for line-reflect-match) may be substituted for TRL.
Since a well matched termination is, in essence, an infinitely long transmission line, it is well
suited for low (RF) frequency calibrations. Achieving a long line standard for low frequencies
is often times physically impossible.

Improving Raw Source Match and Load Match for TRL*/LRM* Calibration

A technique that can be used to improve the raw test port mismatch is to add high quality fixed attenuators.
The effective match of the system is improved because the fixed attenuators usually have a return loss that
is better than that of the network analyzer. Additionally, the attenuators provide some isolation of reflected
signals. The attenuators also help to minimize the difference between the port source match and load
match, making the error terms more equivalent.
With the attenuators in place, the effective port match of the system is improved so that the mismatch of the
fixture transition itself dominates the measurement errors after a calibration.
Figure 7-45 Typical Measurement Set up
If the device measurement requires bias, it will be necessary to add external bias tees between the fixed
attenuators and the fixture. The internal bias tees of the analyzer will not pass the bias properly through the
external fixed attenuators. Be sure to calibrate with the external bias tees in place (no bias applied during
calibration) to remove their effect from the measurement.
Because the bias tees must be placed after the attenuators, they essentially become part of the fixture.
Their mismatch effects are the same for source match and load match, so the TRL CAL routine will correct
) = reverse load match (E
SF
) = forward load match (E
TRL*/LRM* Calibration (ES Models Only)
) = 
LR 11
) = 
LF 22
Operating Concepts
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