Defined Coherence Mode   

With option R&S ZVA-K6, True Differential Mode, the vector network analyzer can also generate several continuous signals with specific relative amplitude and phase. Typical application examples are measurements on balanced DUTs or the supply of antenna arrays which are designed for a well-defined radiation pattern.

True differential mode and defined coherence mode cannot be active at the same time because they require a different source port configuration. Both modes require an analyzer with at least two independent internal sources, i.e. a minimum of 3 ports. Defined coherence mode is compatible with arbitrary single-ended or balanced port configurations.

On R&S ZVA-Z67 network analyzers, all ports have independent internal sources. You can use defined coherence mode with an arbitrary combination of two source ports.
Defined coherence mode can be used for frequency-converting measurements: The two combined ports providing the coherent signal must be at the same frequency. The remaining analyzer ports may measure at a different frequency.   

The source ports and the properties of the coherent signals are all defined in the Defined Coherence Mode dialog. After a system error correction, the coherent signals with the selected properties are available at the calibrated reference plane.

Defined Coherence mode relies on Enhanced Wave Correction. A consistent system error correction is essential for accurate coherent waves at the reference planes. You should always perform a full n-port calibration (TOSM, UOSM or one of the Txx calibration types) of all physical ports involved and change the reference impedances, if they differ from the default settings. A subsequent source power calibration is recommended.
The system error correction applies to all a- and b-waves of the n calibrated ports, not only to the waves with a fixed amplitude and phase relation.  
You can also use offset parameters in order to move the reference plane where the analyzer provides an accurate coherent signal.

Defined Coherence Mode Dialog

Enables the defined coherence mode for signals from different source ports and defines the signal properties.  

• Reference Port selects one of the physical analyzer ports as a reference port. The reference port is the source port for the reference signal; its properties are defined in the Port Configuration dialog. The amplitude and phase of all coherent signals are defined relative to the reference signal.

• Gen ensures a permanent signal; it is identical with the Gen setting in the Source section of the Port Configuration dialog. Coherent signals must be permanent. System error corrections must be performed with alternating source signals (Gen off).

• Def'd Phase Coherence defines the signals from the analyzer ports as coherent or non-coherent signals. For coherent signals, the specified amplitude and phase relation is maintained across the entire sweep. Non-coherent signals have an arbitrary relative phase. It is possible to select one signal per internal source as a coherent signal; see Coupled Test Ports.  
  Examples: On a four port analyzer, ports 1 and 2 and ports 3 and 4 uses the same generator (coupled ports). If port 1 is the reference port, either port 3 or port 4 can be selected as the source port for the second, coherent signal.

• Relative Amplitude defines the amplitude of the coherent signals relative to the reference signal. The Relative Amplitude replaces the source power of the port (defined in the Port Configuration dialog)) as long as Def's Phase Coherence is selected.

• Relative Phase defines the phase of the coherent signals relative to the phase of the reference signal; see below.  

Relative phase examples