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The above equation will return a positive dB value. Historically, most instruments are designed to
show Return Loss as a negative dB value. This requires taking the ratio of reflected to incident power
as in the modified equation shown below:
RL’(dB) will be a negative value. Technically this value is known as “Reflection Coefficient” but is
commonly termed Return Loss in Return Loss meters and Network Analyzers.
Return Loss is related to both SWR and reflection coefficient. Decreasing return loss is measurement
of how well antenna system components are impedance matched. A low return loss indicates a better
match in components and also indicates a lower “Insertion Loss.”
Return Loss is often a preferred measurement over SWR as it has a better resolution for small values
of reflected waves.
Tips:
1.
See the Tips for SWR as they apply equally to Return Loss measurements.
2.
Generally, If you draw a horizontal line at the -20dB mark on the measurement screen, the
Return Loss values below that line indicate a good usable frequency range for that antenna
system. On the BRAVO EX2 you can position Cursor A at the low frequency mark with a -20dB
reading and Cursor B at the high frequency
-20dB mark to see the usable frequency range clearly
between the Cursors from low to high frequency.
SWR and Return Loss Measurement Steps
SWR or Return Loss Measuring
1.
Connect the test lead and any adapter, if they are to be removed from the
measurements.
2.
Press the SWR/RL key to select desired measurement.
3.
Either select Broadband Calibration or perform the “Frequency Specific Calibration” (instructions
described earlier in this Section).
4.
When calibration is complete connect the antenna or other device to be tested, aka DUT
(Device Under Test).
5.
Use the Scale key to adjust the SWR or Return Loss scale for the best plot presentation.
6.
Press the Cursor
key to select Cursor A or A & B with ∆ reading. Use Left/Right Arrow keys to
adjust Cursor positions as desired. Press Cursor key to select active Cursor for arrows control.
7.
If Broadband Calibration was used, the frequency band can be adjusted without
recalibration.
8.
If Frequency Specific Calibration was used you will need to disconnect the DUT from the test
lead or N connector press Freq key, select new frequency range and perform the Frequency
Specific Calibration with the new frequency range.
9.
SWR/RL key will switch between those two measurements with no recalibration. Use the
Scale key to cycle the scale to the best plot presentation.
10.
(Optional) To save the plot press the Memory key and use alpha numeric keys to enter a
name, then press ENTER to save.
