Agilent Technologies 8163A User Manual page 175

A Background to Return Loss Measurement
Agilent 8163A/B, 8164A/B, and 8166A/B User's Guide, Fourth Edition
That is:
where:
The constants t , t , k
1 2 1
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
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 154, the reflection factor of
the component is known. Here we refer to the reflection factor as R
This gives the following equation:
P
For "Measuring the Power when there are No Reflections" on
page 172, the value of the reflection factor is zero. This gives the
following equation:
For "Measuring the Reflections from the DUT" on page 173, the value
of the reflection factor of the DUT is called R
following equation:
P
D UT
P = t k k P R + t s M
2 1 2 src 2
M = t P
1 src
t
2
--- - k
c = k
1 1 2
t
1
t
2
--- - s
c =
2
t
1
P = c M R + c M
Þ
1 2
and k are multipliers giving the proportion of
2
= c M R + c
Ref 1 Re f Ref 2
P = c M
para 2
para
DUT
= c M R + c
1 DU T DU T 2
Return Loss Measurement
(1)
2
Ref
(2)
M
Ref
(3)
. This gives the
(4)
M
DU T
175
.