unbalance-balance conversion is the simulation of one or more unbalance-balance transformers (baluns) integrated in the measurement circuit in order to convert the DUT ports from an unbalanced state into a balanced state and virtually separate the differential and common mode signals. The analyzer measures the unbalanced state but converts the results and calculates mixed mode parameters, e.g. mixed mode S-parameters. No physical transformer is needed.
To perform balanced measurements, a pair of physical analyzer ports is combined to form a logical port. The balanced port of the DUT is directly connected to the analyzer ports
unbalance-balance conversion avoids the disadvantages of real transformers:
There is no need to fabricate test fixtures with integrated baluns for each type of DUT.
The measurement is not impaired by the non-ideal characteristics of the balun (e.g. error tolerances, limited frequency range).
Calibration can be performed at the DUT's ports. If necessary (e.g. to compensate for the effect of a test fixture), it is possible to shift the calibration plane using length offset parameters.
Differential and common mode parameters can be evaluated with a single test setup.
Defining a logical ports requires two physical analyzer ports. The ports of an analyzer are equivalent and can be freely combined. Moreover, it is possible to assign arbitrary, independent reference impedance values to each unbalanced port and to the differential and common mode of each logical port. The following types of balanced devices can be measured with 2-port, 3-port and 4-port analyzers:
2-port analyzers: Reflection measurements on 1 balanced port
3-port analyzers: Reflection and transmission measurements on 1 balanced port
4-port analyzers: Reflection and transmission measurements on 1 or 2 balanced ports
A balanced port configuration is defined by simply selecting the pairs of physical ports that are combined to form balanced ports and defining the two reference impedances for the differential and common mode at each balanced port. All this is done in the Balanced and Measured Ports dialog. The most commonly used balanced port configurations and impedances are predefined and can be selected in the Measurement Wizard.
Depending on the test setup, the analyzer provides different types of mixed mode parameters.
Performing
a balanced measurement
