Agilent Technologies 4294A Specifications download pdf (Page 71)

4-6-8. Practical compensation technique

The calibration and compensation methods suitable for measurement are different for how the test

cable or fixture is connected to the test port. The following is a typical guideline for selecting appro-

priate calibration and compensation methods.

(1) Measurements using Agilent test fixture without test port extension

To make measurements using a test fixture connected directly to the test port, first perform calibra-

tion at the test port. After calibration is completed, connect the test fixture to the test port and,

then perform electrical length compensation (for the test fixture’s electrical length) and open/short

compensation.

(2) Measurement using test port extension

When the measurement needs to be performed using a test port extension or a non-Agilent test fix-

ture, it is recommended that the open/short/load calibration be performed at the measurement ter-

minals of the test fixture. Typically, this method is applied to such a case where unknown devices

are measured using a component handler. Because coaxial terminations do not match geometrically

with the contact terminals of the test fixture or of the component handler, short and load devices

whose values are defined or accurately known are required as substitution standards. (Open cali-

bration requires no device.) Compensation is not required because measurements are made at the

calibration plane.

4-7. Measurement correlation and repeatability

It is possible that different measurement results are obtained for the same device when the same

instrument and test fixture is used. There are many possible causes of the measurement discrepan-

cies, as well as residuals. Typical factors of the measurement discrepancies in RF impedance mea-

surements are listed below.

• Variance in residual parameter value

• A difference in contact condition

• A difference in open/short compensation conditions

• Electromagnetic coupling with a conductor near the DUT

• Variance in environmental temperature

4-7-1. Variance in residual parameter value

Effective residual impedance and stray capacitance vary depending on the position of the DUT con-

nected to the measurement terminals. Connecting the DUT to the tip of the terminals increase

residual inductance compared to when the DUT is at the bottom. Stray capacitance also varies with

the position of the DUT. See Figure 4-17.

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Agilent Technologies 4294A Specifications Page 71