Chapter 4: Single- and Multiport Networks
Ever since single- and multiple port networks were first introduced into the electrical engineering profession through Guillemin and Feldkeller, they have quickly become indispensable tools in restructuring and simplifying complicated circuits as well as in providing fundamental insight into the performance of active and passive electronic devices. Moreover, the importance of network modeling has extended far beyond electrical engineering and has influenced such diverse fields as vibrational analysis in structural and mechanical engineering as well as biomedicine. For example, today's piezoelectric medical transducer elements and their electrical-mechanical conversion mechanisms are most easily modeled as a three-port network.
The ability to reduce most passive and active circuit devices, irrespective of their complicated and often nonlinear behavior, to simple input-output relations has many advantages. Chief among them is the experimental determination of input and output port parameters without the need to know the internal structure of the system. The "black box" methodology has tremendous appeal to engineers whose concern is mostly focused on the overall circuit performance rather than the analysis of individual components. This approach is especially important in RF and MW circuits, where complete theoretical field solutions to Maxwell's equations are either too difficult to derive or provide more information than is normally needed to develop functional, practical designs involving systems such as filters, resonators, and amplifiers.
In the following sections, our objective is to establish the basic network input-output parameter relations, including impedance, admittance, hybrid, and ABCD-parameters for linear circuits. We then develop conversions between these sets. Rules of connecting networks are presented to show how more complicated circuits can be constructed by series and parallel connections as well as cascading of individual network blocks. Finally, the scattering parameters are presented as an important practical way of characterizing RF/MW circuits and devices through the use of power wave relations.