A Background to Return Loss Measurement Return Loss Measurement
Agilent 8163A/B, 8164A/B & 8166A/B Mainframes, Sixth Edition 193
That is:
where:
The constants t
1
, t
2
, k
1
and k
2
are multipliers giving the proportion of
power transmitted through the coupler from the Input port to the Output
port and from the Output port to the sensor port respectively. In other
words, when optical power is input at the Output port, k
2
times that power
is output at the sensor port. It is not necessary to know the value for these
constants, they can be eliminated later.
The constant s is a multiplier giving the scattering factor. The scattering
factor accounts for the directivity of the second coupler, backscatter in the
fiber, and reflections of connectors. The calibration procedure helps you to
eliminate the affect of these on return loss measurements.
For “Return Loss Measurement” on page 171, the reflection factor of the
component is known. Here we refer to the reflection factor as R
Ref
. This
gives the following equation:
For “Measuring the Power when there are No Reflections” on page 190,
the value of the reflection factor is zero. This gives the following equation:
For “Measuring the Reflections from the DUT” on page 191, the value of
the reflection factor of the DUT is called R
DUT
. This gives the following
equation:
P
Ref
c
1
M
Ref
R
Ref
c
2
M
Ref
+=
(2)
P
para
c
2
M
para
=
(3)
P
DUT
c
1
M
DUT
R
DUT
c
2
M
DUT
+=
(4)
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