Characteristics parameters of the two port network

Jun 17 • Notes • 25961 Views • 13 Comments on Characteristics parameters of the two port network

The characteristics parameters of the two port network are given below:

Image Impedance

It is the impedance which when connected to the input and the output of the transducer,it will make both the impedances equal at the input and the output terminal.It is basically the concept which is used in the field of the network analysis and design and also in the field of the filter design.It applies to the seen impedance which is determined by looking through the ports of the network.

The Two-port network can be properly used to describe the concept of the image impedance in the better way.

two port network

two port network

The impedance zi1 – when considered from the port 1

Zi2 –image impedance when considered from the port 2

The image impedance will not be equal until the network is the symmetrical network or anti-symmetrical with respect to the ports.

Characteristic impedance

The characteristics impedance also known as the surge impedance is usually considered in the case of the transmission line and is represented as Z0. The characteristics impedance is defined as the ratio of the amplitude of the voltage and the current taking the consideration of  the single wave through the line.The surge impedance is usually allocated through the transmission line with its geometry and the material.It is to be noted that this impedance is independent of the line length.SI unit – ohm


It is defined as the particular value of the load impedance which has the ability to produce an input impedance with the value as same as the value of the load impedance.In the two port system when it is connected at the one end then it produces equal impedance when looking at each other.

Image transfer coefficient

It is usually considered for the linear passive type of the two-port network,such network must be terminated with the image impedance of the network.Let

V1 – voltage at the input terminal

I1 – current at the input terminal

V2 – voltage at the output terminal

I2 – current at the input terminal

Hence,the image transfer coefficient can be calculated as half the logarithm of the product of V1 andI1 divided by the product of the V2 and I2 .

Represented as,

½  log ((V1 I1 ) / (V2 I))

Propagation constant

This constant is usually considered for the wave and is defined as change in the phase angle with respect to the per unit change in the distance travelled by the wave.In other words we can say as the rate of the change in the phase of wave with distance.The constant is represented as  the term K.

Lattice and bridged network

A network that is made up  of four branches connected in series to form a mesh; two nonadjacent junction points serve as input terminals, and the remaining two junction points serve as output terminals.The lattice networks are being widely used in the areas like  grid computing,sensor networks  and in many more areas.The main points which highlights the lattice networks are

1)Its optimal routing policies

2)limits on the capacities of its elements

3)Its performance with the finite amount of the buffers

A bridge-T network with a fourth branch connected between an input and an output terminal and across two branches of the network.

Insertion Loss

The insertion loss can be explained as the loss in load power because of the insertion of a particular component or device  in a transmission system.It is represented in the ratio of the decibels of the power received at the side of the load before the insertion of the component to the power received at the load side after the insertion of the component or the device. 


An Attenuator is  a special type of electrical bidirectional circuit made up of entirely resistive elements. It is nothing but a two port resistive network designed to weaken or attenuate the power being supplied by a source to a level that is suitable for the connected load.The amount of the power is reduced which is being delivered the load. These have the basic applications in radio, communication and transmission line etc.

Attenuator Connection

The network of the attenuator  can be designed to produce a fixed degree of attenuation or to give a variable amount of attenuation.The standard attenuators networks generally known as an attenuator  pad are available from 0dB to more than 100dB. The Variable and switched attenuator are the adjustable resistor type of the networks that show a calibrated increase in attenuation for each switched step.

attenuator connection

attenuator connection

Simple passive attenuators

Attenuators are the reverse of amplifier which  reduces gain with the resistive voltage divider circuit. The amount of attenuation  is determined by the ratio of output/input in the network.

However using voltage , current or even power ratios to determine or express the amount of attenuation that a resistive attenuator network may have the attenuation factor, can be confusing, so far the passive attenuator its degree of attenuation is normally expressed using a logarithm scale which is given in decibels making it easier to deal with small numbers.

Degrees of Attenuation

An attenuators performance is expressed by the number of decibel the input signal has decreased per frequency decade.

Decibel attenuation

dBv = 20log10 Vout/Vin (dB)

Decibel is logarithmic ratio therefore has no units.

Symmetrical & assymetrical attenuators

Symmetrical attenuator:

A perfectly symmetrical attenuator is that whose input and output terminals can be transposed.

T-pad attenuator, Pi-pad attenuator, and bridge-T attenuator is a symmetrical attenuator.

T-pad Attenuator

It is an unbalanced type of the attenuator network which consists of three non-inductive type of the  resistive elements connected  to form T configuration.

T-pad attenuator

T-pad attenuator

The T-Pad attenuator is symmetrical in its design when we  look from either end and this attenuator design can be used to impedance match either equal or unequal transmission lines.

Bridge-T Attenuator

It is another purely resistive design that is a variation on the symmetrical T-pad attenuator. As it name implies the bridged-T attenuator has an additional resistive element forming a bridge network across the two series resistors of the standard T-pad. This additional resistors enables the circuit to reduce the level of a signal appears to bridge across the T-pad network.

bridge - T attenuator

bridge – T attenuator

Asymmetrical Attenuator:

It can match the impedance in only one direction. It can be either  balanced or unbalanced.

It is simply a voltage divider circuit used in electrical & electronic circuit  to generate a lower voltage. The difference this time is that this type of attenuator is used in frequency dependent circuit to create loss in transmission or to match the impedance of unbalanced source and load networks. The L-pad attenuator network comprises of two purely resistive elements in series with each other connected across a voltage source.


unsymmetrical attenuator

unsymmetrical attenuator

Related Questions and answers

Q.what is image impedance??

The image impedance as the type of the impedance which when connected to the input and the output of the transducer it will make both the impedances equal.

Q.what is iterative impedance??

It is defined as the particular value of the load impedance which has the ability to produce an input impedance with the value same as the value of the load impedance.

Q.what is meant by insertion loss??

It is defined in the load power due to the insertion of the component or device at some point in the transmission system.

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13 Responses to Characteristics parameters of the two port network

  1. Anonymous says:
  2. Anonymous says:
  3. Simbarashe says:
  4. Jhansi says:


  5. parmesh kumar yadav says:


  6. parmesh kumar yadav says:


  7. Abdul Ahad says:

    in two port network if i take inpuserially and ouput parrallely then what will be the charateristics

  8. aishwarya r dhoot says:

    give parameters of filters in network analysis & define propagation constant

  9. Barun Singh says:

    A great and needful information for an electrical student or may be for any stream electrical student.I electrical engineering almost every instrument is made up of 2 port devices like In motor Input port is electrical supply and the output port is mechanical works.there are many more examples like transformer generators etc

  10. Shivangi Nupur says:

    this article reads about…..Characteristics parameters of two port network, it gives brief description of two port network, its concepts,principles and thoeries have been well explained. This article is for electrical and electronic students .

  11. boopathy sathish says:

    Characteristics parameters of two port network, A complete knowledge of two port network, its concepts and principles have been well explained. This article helps electrical and electronic students very much.

  12. Seetha Manoharan says:

    Two port networks having more importance in electronics. this article is helpful to know its characteristics.

  13. Dinesh says:

    This a very interesting concept.
    and raising my expectation about this article

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