The analysis of passive two-port networks is an outgrowth of reciprocity theorems first derived by Lorentz.In two-port mathematical models, the network is described by a 2 by 2 square matrix of complex numbers. Any linear circuit with four terminals can be regarded as a two-port network provided that it does not contain an independent source and satisfies the port conditions.Įxamples of circuits analyzed as two-ports are filters, matching networks, transmission lines, transformers, and small-signal models for transistors (such as the hybrid-pi model). For example, transistors are often regarded as two-ports, characterized by their h-parameters (see below) which are listed by the manufacturer. It also allows similar circuits or devices to be compared easily. This allows the response of the network to signals applied to the ports to be calculated easily, without solving for all the internal voltages and currents in the network. A two-port network is regarded as a "black box" with its properties specified by a matrix of numbers.
The two-port network model is used in mathematical circuit analysis techniques to isolate portions of larger circuits. In a two-port network, often port 1 is considered the input port and port 2 is considered the output port. The ports constitute interfaces where the network connects to other networks, the points where signals are applied or outputs are taken. Two terminals constitute a port if the currents applied to them satisfy the essential requirement known as the port condition: the electric current entering one terminal must equal the current emerging from the other terminal on the same port. A two-port network (a kind of four-terminal network or quadripole) is an electrical network (circuit) or device with two pairs of terminals to connect to external circuits.
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