Technical data

390 Chapter 14
Return Loss
Measuring Return Loss
Return Loss
Measuring Return Loss
Return loss is a measure of reflection characteristics. One way you can use the
return loss measurement is to detect problems in the antenna feedline system and the
antenna itself. A portion of the incident power will be reflected back to the source
from each transmission line fault as well as the antenna. The ratio of the reflected
voltages to the incident voltage is called the reflection coefficient. The reflection
coefficient is a complex number, meaning it has both magnitude and phase
information. In S-parameter terms, Return Loss is referred to as an S
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measurement.
NOTE Test signals can cause interference. When testing cables attached to antennas, test
signals are radiated. Verify that the signal used for the test cannot cause interference
to another antenna.
Calibration - Minimizing your Workload
The Return Loss calibration is the same calibration as performed for the One Port
Insertion Loss
and Distance to Fault (when it is performed with Frequency Range
set to manual) measurements. If you have already calibrated for any of these three
measurements, the calibration will apply to the other two measurements and
“Calibrated” (together with the frequency range over which the calibration was
performed) will be displayed on top left of the screen for all three if the Start and the
Stop frequencies are set within the calibrated frequency range.
The
Distance to Fault calibration (when it is performed with Frequency Range set
to Auto) is only valid for other Distance to Fault measurements that are also
performed with Frequency Range set to Auto, and then only if the Start and the Stop
Frequencies fall within the previously calibrated frequency range.
If you have not previously performed a calibration, the word “Uncalibrated” appears
at the top left of the measurement screen.
It is important that you keep the calibration frequency range as close as possible to
the actual sweep frequencies you intend using for the measurement or
measurements. Calibrating over a large frequency range (for example, 1 GHz) when
you only intend measuring over a much smaller range (a few kHz, for example) will
reduce your measurement accuracy.
If you plan to perform a combination of
One-Port Insertion Loss measurement,
Return Loss measurement, and Distance to Fault measurements using a frequency