Chapter 5 5-7
Making GSM Cable and Antenna Measurements
Making Return Loss Measurements
Making Return Loss Measurements
Purpose
Some of the energy incident upon a device can be reflected back towards
the source. A return loss measurement quantifies this reflected energy.
Return loss is used to determine the health of an antenna system and
its associated cabling by measuring the amount of transmitted power
reflected back from the antenna system and therefore not passed over
the air interface to the mobile user.
Cables and antennae are often subjected to harsh weather conditions
resulting in a performance which deteriorates over time, leading to an
eventual failure. By monitoring return loss over time, cable and
antennae performance can be monitored and preventive action taken
when required.
Making the measurement
NOTE A return loss measurement requires the use of a signal separation
device such as a directional coupler or bridge in addition to the device
being tested for return loss.
NOTE The spectrum analyzer must be in spectrum analyzer mode for this
measurement.
1. Connect the tracking generator, signal separation device, device
being measured and the spectrum analyzer input as shown in
Figure 5-4
Figure 5-4 Return Loss Measurement Set-up
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