An admittance is the complex ratio between a current and a voltage. The analyzer provides two independent sets of admittance parameters:
Converted admittances (each admittance parameter is obtained from a single S-parameter)
Y-parameters (complete description of the n-port DUT)
The converted admittance parameters describe the input admittances of a DUT with fully matched outputs.The converted admittances are the inverse of the converted impedances.
The analyzer converts a single measured S-parameter to determine the corresponding converted admittance. As a result, converted Y-parameters cannot completely describe general n-port DUTs:
A reflection parameter Yii completely describes a one-port DUT. For n-port DUTs (n>1) the reflection parameters Yii describe the input admittances at ports i (i = 1 to n) under the condition that each of the other ports is terminated with its reference impedance (matched-circuit parameters).
A two-port transmission parameter Yij (i ≠ j) can describe a pure serial impedance between the two ports.
The converted admittances Yii are calculated from the reflection S-parameters Sii according to:
The transmission parameters are calculated according to:
Examples:
Y11 is the input admittance of a 2-port DUT that is terminated at its output with the reference impedance Z0 (matched-circuit admittance measured in a forward reflection measurement).
The extension of the admittances to more ports and mixed mode measurements is analogous to S-parameters. Ydd44 is the differential mode input admittance at port 4 of a DUT that is terminated at its other ports with the reference impedance Z0. See More Admittances for detailed information.
You can also read the converted admittances in a reflection
coefficient measurement from the inverted
Smith chart.
The Y-parameters describe the admittances of a DUT with output ports terminated in a short circuit (V = 0). The analyzer provides the full set of Y-parameters including the transfer admittances (i.e. the complete n x n Y-matrix for an n port DUT).
This means that Y-parameters can be used as an alternative to S-parameters (or Z-parameters) in order to completely characterize a linear n-port network.
In analogy to S-parameters, Y-parameters are expressed as Y<out>< in>, where <out> and <in> denote the output and input port numbers of the DUT.
In analogy to Z-parameters, the Y-parameters for a two-port are based on a circuit model that can be expressed with two linear equations:
The four 2-port Y-parameters can be interpreted as follows:
Y11 is the input admittance, defined as the ratio of the current I1 to the voltage V1, measured at port 1 (forward measurement with output terminated in a short circuit, V2 = 0).
Y21 is the forward transfer admittance, defined as the ratio of the current I2 to the voltage V1 (forward measurement with output terminated in a short circuit, V2 = 0).
Y12 is the reverse transfer admittance, defined as the ratio of the current I1 to the voltage V2 (reverse measurement with input terminated in a short circuit, V1 = 0).
Y22 is the output admittance, defined as the ratio of the current I2 to the voltage V2, measured at port 2 (reverse measurement with input terminated in a short circuit, V1 = 0).
Y-parameters can be easily extended to describe circuits with more than two ports or several modes of propagation; see section More Y-Parameters.
