- Impedance parameters
Impedance parameters or Z-parameters are properties used in
electrical engineering ,electronics engineering , and communication systems engineering describe the electrical behavior oflinear electrical network s when undergoing various steady state stimuli by small signals. They are members of a family of similar parameters used in electronics engineering, other examples being:S-parameters , [David M. Pozar, "Microwave Engineering", Third Edition, John Wiley & Sons Inc., 2005; pp. 170-174, ISBN 0-471-44878-8.]Y-parameters , [David M. Pozar, 2005 (op. cit); pp 170-174.]H-parameters ,T-parameters orABCD-parameters . [David M. Pozar, 2005 (op. cit); pp 183-186.] [A.H. Morton, " Advanced Electrical Engineering", Pitman Publishing Ltd., 1985; pp 33-72, ISBN 0-273-40172-6.]The General Z-Parameter Matrix
For a generic multi-port network definition, it is assumed that each of the ports is allocated an integer 'n' ranging from 1 to N, where N is the total number of ports. For port n, the associated Z-parameter definition is in terms of input currents and output voltages, and respectively.
For all ports the output voltages may be defined in terms of the Z-parameter matrix and the input currents by the following matrix equation:
:
where Z is an N x N matrix the elements of which can be indexed using conventional matrix notation. In general the elements of the Z-parameter matrix are
complex number s.The phase part of a Z-parameter is the "spatial" phase at the test frequency, not the temporal (time-related) phase.
Two-Port Networks
The Z-parameter matrix for the
two-port network is probably the most common. In this case the relationship between the input currents, output voltages and the Z-parameter matrix is given by::.
where
:
:
For the general case of an n-port network, it can be stated that:
Impedance relations
The input impedance of a two-port network is given by:
:
where ZL is the impedance of the load connected to port two.
Similarly, the output impedance is given by:
:
where ZS is the impedance of the source connected to port one.
Converting Two-Port Parameters
The two-port S-parameters may be obtained from the equivalent two-port Z-parameters by means of the following expressions. [Simon Ramo, John R. Whinnery, Theodore Van Duzer, "Fields and Waves in Communication Electronics", Third Edition, John Wiley & Sons Inc.; 1993, pp. 537-541, ISBN 0-471-58551-3.]
:
:
:
:
Where
:
The above expressions will generally use complex numbers for and . Note that the value of can become 0 for specific values of so the division by in the calculations of may lead to a division by 0.
S-parameter conversions into other matrices by simply multiplying with e.g. are only valid if the characteristic impedance is not frequency dependent.
Conversion from
Y-parameters to Z-parameters is much simpler, as the Z-parameter matrix is basically thematrix inverse of the Y-parameter matrix. The following expressions show the applicable relations::
:
:
:
Where
:
In this case is the
determinant of the Y-parameter matrix.References
Bibliography
*David M. Pozar, "Microwave Engineering", Third Edition, John Wiley & Sons Inc.; ISBN 0-471-44878-8.
*Simon Ramo, John R. Whinnery, Theodore Van Duzer, "Fields and Waves in Communication Electronics", Third Edition, John Wiley & Sons Inc.; ISBN 0-471-58551-3.ee also
*
Scattering parameters
*Admittance parameters
*Two-port network
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