Measuring Impedance Magnitude; How The Reflection Measurement Works - HP 8712ES User Manual

Making Measurements

Measuring Impedance Magnitude

Measuring Impedance Magnitude
The impedance (Z) of a DUT can be calculated from the measured
reflection or transmission coefficient. The impedance magnitude format
allows measurement of impedance versus frequency or power. This
measurement can be useful for many types of devices, including
resonators and discrete passive components.
The analyzer measures the reflection or transmission response of the
DUT, converts it to the equivalent complex impedance, and displays the
magnitude. Two simple conversions are available, depending on the
measurement configuration.
An accurate impedance measurement is highly dependent on a good
calibration. The accuracy of the impedance measurement is best when
the measurement results are near the analyzer's system impedance (50
or 75 ohms). The resolution is limited (by internal math calculations) to
approximately 5 to 10 milliohms.
To use the impedance magnitude format, press
FORMAT
More Format Impedance Magnitude
.
How the Reflection Measurement Works
A reflection trace can be converted to equivalent impedance using the
model and equations shown in Figure 3-36, "Impedance Calculation for
3-36, Γ is the
Reflection Measurements." In the formula shown in Figure
complex reflection coefficient. The complex impedance, Z , is computed
Refl
based on Γ and Z
. The analyzer displays the magnitude of Z . This
0 Refl
measurement assumes a two-terminal device, connected between the
analyzer's test ports.
3-80 ES User's Guide