ABSTRACT
This chapter presents the concept of n-port as that of a circuit structure whose interaction with the outside world takes place through n terminal pairs or ports. It also presents the general physical properties of such structures. The chapter introduces still another representation derivable from the general description. This involves the so-called scattering matrix which always exists whenever the n-port is passive and well defined. For the sake of definiteness, the chapter deals with n-ports composed of a finite number of ideal resistors, inductors, capacitors, gyrators, transformers, independent and dependent voltage and current generators. The equations of an n-port are obtained from those of the complete network on which it is based by first omitting the equations of the terminations and then eliminating the internal variables. To obtain a representation corresponding to a set of ordinary differential equations with constant coefficients in the time domain, the original equations must have coefficients which are polynomials.
