Chapter 5 5-9
Making GSM Cable and Antenna Measurements
Making Return Loss Measurements
Example
The following example measures the return loss of a bandpass filter
(BPF).
1. Adjust the spectrum analyzer control settings.
With the BPF in the measurement path, adjust the spectrum
analyzer control settings for the correct frequency coverage,
resolution bandwidth, input attenuation and source power.
NOTE Having adjusted the control settings, do not alter them during the
course of the measurement.
To obtain a faster sweep, change the coupling from normal spectrum
analyzer mode to stimulus response mode by pressing the
Sweep
front panel key and Swp Coupling SR SA menu key until SR is
underlined.
2. Establish a 0 dB reference trace for normalizing the measured data.
Normalization removes any frequency-response errors introduced by
the components of the test setup before making the measurement. It
is performed by removing the device to be tested and measuring a
short or open. As neither can dissipate the energy of the incident
signal—100% reflection takes place, the wave is reflected back from
the short or open—that is, 100% reflection takes place—to the
spectrum analyzer where its value is displayed:
a. Remove the BPF and connect a short in its place as shown in
Figure 5-5.
b. Press the
View/Trace front panel key.
c. Press the
More menu key.
d. Press the
Normalize menu key, Store Ref (1 - 3) and normalize On.
This procedure establishes a 0 dB reference trace which is stored in
the ESA/spectrum analyzer. It is then used to normalize the
measured data automatically by subtracting the short circuit
calibration from the measurement obtained with the device.
3. Make the measurement.
a. Re-connect the device in place of the short/open.
b. Read the measurement and save it if required.
The return loss of the device is displayed on the screen. Use the
marker to evaluate the result and save the trace if required.
An example is shown in Figure 5-6 on page 5-10.
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