Agilent Technologies 8719D, User Manual

Page: 370 / 673

If the device measurement requires bias, it will be necessary to add external bias tees between
the attenuators and the The internal bias tees of the analyzer will not pass the
bias properly through the external 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. Therefore, their mismatch effects on the measurement will not be improved by the
attenuators.
Although the attenuators improve the raw mismatch of the network analyzer system,
they also degrade the overall measurement dynamic range.
This effective mismatch of the system after calibration has the biggest effect on reflection
measurements of highly reflective devices. Likewise, for well matched devices, the effects of
mismatch are negligible. This can be shown by the following approximation:
Reflection magnitude uncertainty = En +
+ +
Transmission magnitude uncertainty = + + +
where:
= effective directivity
En effective reflection tracking
effective source match
effective load match
effective crosstalk
effective transmission tracking
S-parameters of the device under test
The Calibration Procedure
Requirements for Standards
When building a set of TRL standards for a microstrip or fixture environment, the requirements
for each of these standard types must be satisfied.
Requirements
THRU (Zero
q
No loss. Characteristic impedance ) need not be known.
1
THRU
(Non-zero
•I of the thru must be the same as the line (if they are not the same, the
average impedance is used).
q
Attenuation of the thru need not be known.
q
If the thru is used to set the reference plane, the insertion phase or
electrical length must be well-known and specified. If a non-zero length
thru is specified to have zero delay, the reference plane is established in the
middle of the thru.