View And Interpret The Reflection Measurement Results - HP 8712ET User Manual

View and Interpret the Reflection
Measurement Results
1. To view the entire measurement trace on the display, press
Autoscale
.
2. To interpret the reflection measurement, refer to
"Example of a Reflection Measurement Display,"
display if you are making this measurement on your instrument.
a. The values shown on the horizontal axis are the frequencies in
MHz. The values shown on the vertical axis are the power ratios
in decibels (dB) of the reflected signal divided by the incident
power. To display the result in logarithmic magnitude format
(designated by Log Mag at the top of the measurement screen),
the analyzer computes the measurement trace using the following
formula:
where P = the power of the signal reflected from the device and
refl
where P = the incident power.
inc
b. A level of 0 dB indicates that all of the power applied to the DUT is
reflected back, and that none of it passes through the DUT or is
absorbed by the DUT.
c. Values less than 0 dB indicate that power is either absorbed or
transmitted by the DUT. Although they are not typically seen,
values greater than 0 dB do occur under certain circumstances
such as when the measurement needs to be enhanced by
calibration, or when the device is active (an amplifier for instance)
and perhaps oscillating.
ET User's Guide
( )
Reflection dB =
Making Measurements
Measuring Reflection Response
SCALE
Figure 3-17,
or your analyzer's
P
 
refl
----------
10 log
 
P
inc
,
3-37