View And Interpret The S11 Measurement Results - HP 8712ES User Manual

Making Measurements
Measuring S11 Reflection Port 1 using a One-Port Calibration
View and Interpret the S11 Measurement
Results
1. To view the entire measurement trace on the display, press
Autoscale .
2. To interpret the reflection measurement, refer to
"Example of an S11 Measurement 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:
( )
Reflection dB
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 not commonly seen, values
greater than 0 dB can 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.
3-54
P
 
refl
----------
= 10 log
 
P
inc
SCALE
Figure 3-21,
or your analyzer's display
ES User's Guide