Chapter 12 12-23
Theory of Operation
Signal Separation (8753ET)
Signal Separation (8753ET)
The A21 Dual Directional Coupler
Signal separation in the analyzer is accomplished with a dual directional coupler which, by
itself, comprises the analyzer’s built-in test set. The dual directional coupler is connected
to the reflection test port. It is used to separate the incident signal going to the device
under test from reflected signals coming from the device under test. A portion of the
incident signal is applied to the R sampler/mixer via one of the coupled arms of the dual
directional coupler. Meanwhile, the reflected signal is routed from the reflection test port
via the other coupled arm to the input of the A sampler/mixer in the receiver.
If the 8753ET network analyzer is equipped with a step attenuator in the source assembly
(Option 004), one of the coupled arms of the dual directional coupler is not used for
transmitting part of the incident signal to the R sampler/mixer. Instead, the R sampler
signal is taken directly from the source prior to the step attenuator.
Signals applied to the transmission test port are fed directly to the B sampler/mixer.
Figure 12-9 8753ET Dual Directional Coupler without Option 004
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