## Two Port Network Two Port Network

Network:-
When a number of impedance are connected together to form a system that consists of interconnected circuits performing specific or assigned functions’ it is called a “network” or circuit.

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An “Electrical network” with which the present text is concerned is a combination of numerous electric element (e.g. R’L’C etc).

Network element:-
A network element is a component of a circuit having different characteristics.

Types of network element:-
• Linear and nonlinear elements
• Active & passive elements
• Unilateral and bilateral elements.

Linear and non-linear elements:-
A linear elements shows linear characteristics of voltage Vs current simple R’L’C are linear elements. The value of resistance’ inductance and capacitance do not change with a change in applied voltage.
For non-linear elements the current passing through it does not change linearly with the linear change in applied voltage at a particular frequency. Semi-conductor device are usually. Examples of non- linear elements.

Active and passive components:-
If a circuit elements has the capability of enhancing the energy level of a signal passing through it. It is called on active elements. Vacuum tubes and semi-conductor devices are active elements.
If a circuit elements do not have capability to enhance the energy level of the signals are known as passive elements.

Unilateral and bilateral elements:-
If the magnitude of the current passing through an element is affected due to change in the polarity of the applied voltage. Then the element is called unilateral element.
If the current magnitude remains the same even if the applied e.m.f’s polarity is changed, it is called a bilateral element.
Unilateral elements offer varying impedances with variations in flow of current.
Bilateral elements offer same impedance irrespective of flow of current.
A resistor, inductor, capacitor are bilateral network elements.
Diodes, transistor etc are unilateral elements.

Classification of network:-
On the basis of network elements the networks are classified as

Linear network:-
That network or circuits whose parameters remain constant with change in applied voltage or current are called linear networks. Linear networks obeys ohm’s law i.e. IV.
Examples: -  Resistance, inductance, capacitance.

Non linear network:-
That network whose parameters change with change in applied voltage or current are called non linear networks. Non linear network not obeys ohm’s law i.e. I.
Examples: - diodes, transistors.

Unilateral networks:-
It is a circuit or network whose characteristic or properties is change due to chnge in direction of current is called unilateral network.
Examples: - diodes, transistors.

Bilateral network:-
It is a network or circuit whose characteristic or properties may not change due to change in direction of current is called bilateral network.
Examples: - elements made of high conductivity material.

Active network:-
That network or circuit which consists of active element like battery or transistor it contains one or more than one voltage source.

Passive network:-
That network or circuit which consists of passive elements i.e. resistance, inductance & capacitance is called passive network passive network does not contain any voltage sources.

Lumped network:-
Electrical networks whose components are physically separable are known as lumped network.

Distributed network:-
Electrical networks whose parameters are not physically separable are known as distributed network.
Example: - transmission line etc.

Recurrent network:-
When a large circuit consists of similar networks connected one after another, the network is called as recurrent network or cascaded network. It is also called as ladder networks.

Non-Recurrent network:-
Single network or circuit is called non-recurrent network.

Classification of network according to port:-
There are three types of network according to port given as.

One port network:-
Any active or passive network having only one pair of terminal that is either connected at input side or output side is called one port network.

Two port network:-
Any active or passive network or circuit having two pair of terminals, where one pair of terminal is connected at input side and other pair of terminal is connected at the output side is called two port networks.

N-port network:-
Any active or passive network or circuit which consists of ‘n’ pair of terminals is called n-port network. In n-port network, the driving source may be considered is more than one pairs of terminals.

Depending up on the shape the network:-
T-type network:-
When a network looks like a alphabet letter ‘T’ is called T-section or ‘T’ type network.

network:-
When a network is looks like as  is known as - network.
L-network:-
When a network looks like L is known as L-network.

Lattice network:-
A lattice network where the series arms are given by the impedances connected between (a & c) and (b and d). The diagonal arms are frequency terms as cross arm.

Bridge T network:-
That network in which the series arms of a T-section are bridged by  an impedance. Then the network is called bridge T-network.

Properties of asymmetrical networks:-
The network which is not symmetrical with respect to its input and output port is known as asymmetrical network.
An asymmetrical network has four electrical characteristics.
1)Iterative impedance
2) Image impedance
3) Image transfer constant
4) Iterative transfer constant.

Iterative impedance:-
The iterative impedance of any network section is defined by a particular impedance of any network section is defined by a particular impedance at its one pair of terminals. When the same impedance is connected across the other pair of terminals. Iterative impedance at the input and output terminals being Zt1 & Zt2 for asymmetrical networks.