Any circuit that is excited by a single, independent source applied to one port and having a load connected to another port can be considered as a two-port circuit. Active, electronic devices and their associated circuits are the prime examples of two-port circuits. A two-port circuit is characterized, in general, by sets of four parameters defined in terms of open-circuit or short-circuit terminations at each port. The analysis based on this characterization provides a useful and powerful alternative to conventional circuit analysis discussed in previous chapters.