Agilent Technologies ENA Series User Manual page 300

Fixture Simulator
Evaluating Balanced Devices (balance-unbalance conversion function)
Figure 7-8 Types of balanced devices that can be evaluated with E5070B/E5071B
In the terminology of the E5070B/E5071B, ports after the balance conversion are called
logical ports (or DUT ports).
You can freely assign the test ports of the E5070B/E5071B to logical ports (ports a to d in
Figure 7-8).
294 Chapter 7