2-50
Making Mixer Measurements (Option 089 Only)
Isolation Example Measurements
SWR / Return Loss
Reflection coefficient (Γ) is defined as the ratio between the reflected voltage (V
r
) and
incident voltage (V
i
). Standing wave ratio (SWR) is defined as the ratio of maximum
standing wave voltage to the minimum standing wave voltage and can be derived from the
reflection coefficient (Γ) using the following equation. Return loss can be derived from the
reflection coefficient as well.
NOTE Mixers are three-port devices, and the reflection from any one port depends
on the conditions of the other two ports. You should replicate the operating
conditions the mixer will experience as closely as possible for the
measurement. For all mixer SWR measurements, use the same power level
that the mixer will use during normal operation.
When you measure the RF port SWR, you should have the LO drive level present and set
to the expected frequency and power levels. Different LO drives and frequencies may yield
different values for SWR at the same RF frequencies. The IF port should be terminated in
a condition as close to its operating state as possible.
The measurements of LO port SWR and IF port SWR are very similar. For IF port SWR,
you should terminate the RF port in a matched condition and apply the LO signal at its
normal operating level. For the LO port SWR, the RF and IF ports should both be
terminated in conditions similar to what will be present during normal operation.
Γ
V
r
V
i
-----=
SWR
1 Γ+
1 Γ–
---------------=
Return loss 20– Γlog
=
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