“Impedance parameters”的意思、由来-开放百科全书

Z-parameters are also known as open-circuit impedance parameters as they are calculated under open circuit conditions. i.e., I_x=0, where x=1,2 refer to input and output currents flowing through the ports (of a two-port network in this case) respectively.

The Z-parameter matrix

A Z-parameter matrix describes the behaviour of any linear electrical network that can be regarded as a black box with a number of ports. A port in this context is a pair of electrical terminals carrying equal and opposite currents into and out-of the network, and having a particular voltage between them. The Z-matrix gives no information about the behaviour of the network when the currents at any port are not balanced in this way (should this be possible), nor does it give any information about the voltage between terminals not belonging to the same port. Typically, it is intended that each external connection to the network is between the terminals of just one port, so that these limitations are appropriate.

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 the port current and port voltage,

and

respectively.

For all ports the voltages may be defined in terms of the Z-parameter matrix and the currents by the following matrix equation:

where Z is an N × N matrix the elements of which can be indexed using conventional matrix notation. In general the elements of the Z-parameter matrix are complex numbers and functions of frequency. For a one-port network, the Z-matrix reduces to a single element, being the ordinary impedance measured between the two terminals.The Z-parameters are also known as the open circuit parameters because they are measured or calculated by applying current to one port and determining the resulting voltages at all the ports while the undriven ports are terminated into open circuits.

Two-port networks

The Z-parameter matrix for the two-port network is probably the most common. In this case the relationship between the port currents, port voltages and the Z-parameter matrix is given by:

Impedance relations

Relation to S-parameters

where

is the identity matrix,

is a diagonal matrix having the square root of the characteristic impedance at each port as its non-zero elements,

and

is the corresponding diagonal matrix of square roots of characteristic admittances. In these expressions the matrices represented by the bracketed factors commute and so, as shown above, may be written in either order.^[5]^[6]

Two port

In the special case of a two-port network, with the same characteristic impedance

at each port, the above expressions reduce to

The two-port S-parameters may be obtained from the equivalent two-port Z-parameters by means of the following expressions^[7]

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.

Relation to Y-parameters

Conversion from Y-parameters to Z-parameters is much simpler, as the Z-parameter matrix is just the inverse of the Y-parameter matrix. For a two-port:

Notes

1. ^{{cite book| author = David M. Pozar| title = Microwave Engineering| date = 2004-02-05| publisher = Wiley| isbn = 978-0-471-44878-5| pages = 170–174 }}
2. ^David M. Pozar, 2005 (op. cit); pp 170-174.
3. ^David M. Pozar, 2005 (op. cit); pp 183-186.
4. ^A.H. Morton, Advanced Electrical Engineering, Pitman Publishing Ltd., 1985; pp 33-72, {{ISBN|0-273-40172-6}}.
5. ^¹²{{cite book| last = Russer| first = Peter| title = Electromagnetics, microwave circuit and antenna design for communications engineering| year = 2003| publisher = Artech House| isbn = 1-58053-532-1 }}
6. ^Any square matrix commutes with itself and with the identity matrix, and if two matrices A and B commute, then so do A and B⁻¹ (since AB⁻¹ = B⁻¹BAB⁻¹ = B⁻¹ABB⁻¹ = B⁻¹A)
7. ^{{cite book| author = Simon Ramo|author2=John R. Whinnery |author3=Theodore Van Duzer | title = Fields and Waves in Communication Electronics| date = 1994-02-09| publisher = Wiley| isbn = 978-0-471-58551-0| pages = 537–541 }}