The document discusses transmission lines, which are used to carry information signals in electrical, optical, or electromagnetic forms. It covers the primary line constants such as resistance, inductance, capacitance, and conductance, and introduces secondary line constants including attenuation, phase shift, and propagation coefficients. Additionally, the attenuation coefficient is defined as the measure of signal strength reduction along a transmission line.

1. Transmission lines
Author: Irfan Sultan
Instructor (Telecom.)
Govt. College of Technology

2. Contents
 Introduction to Transmission Lines
 Transmission Line Parameters
 Transmission Line Equations

3. Transmission Lines
 A transmission line is a medium or structure which is used to carry an information
or data signal from one place to another.
 An information signal can be propagated in the following three forms:
 Electrical
 Optical (Light)
 Electromagnetic (EM) Wave
 Hence there are three main types of transmission lines:
 Wires
 Optical Fibers
 Waveguides

4. Transmission Lines
Wires Optical Fibers Waveguides

5. Transmission Line Parameters
 The quantities which are used to study or show the behavior of a transmission line
are called Primary Line Constants. These are normally called Transmission Line
Parameters.
 There are four Primary Line Constants.
 Resistance (R)
 Inductance (L)
 Capacitance (C)
 Conductance (G)

6. Transmission Line Parameters
 Transmission lines are modeled by means of the parameters resistance, inductance, capacitance
and conductance.
 Resistance and inductance together is called transmission line impedance.
 Capacitance and conductance in parallel is called admittance.
 Resistance: It is also called Loop Resistance per Unit Length. It is equal to the sum of the resistances of both
the conductors of a line. Its unit is Ω/m.
 Inductance: It is also called Loop Inductance per Unit Length. It is equal to the sum of the inductances of both
the conductors of a line. Its unit is H/m.
 Capacitance: It is denoted by C. it is equal to the shunt capacitance per unit length b/w two conductors. Its
unit is farad/m.
 Conductance: It is denoted by G. It is equal to the shunt conductance per unit length b/w two conductors. It is
reciprocal of resistance and is measured in Siemens/m or mho/m.
 Note: R, L, G and C are also called Primary Line Constants of Transmission Line. These values, normally,
vary with frequency but in transmission line theory they are assumed constant.

7. Transmission Line Equations
 The quantities which are used to study or show the effects on a signal which
propagates through a transmission line are known as Secondary Line Constants,
and the equations which are used for these secondary line constants are called
Transmission Line Equations.
 There are the following basic three secondary line constants:
 Attenuation Coefficient
 Phase Shift Coefficient
 Propagation Coefficient
 There are other secondary line constants too (Phase velocity, Velocity Factor and
Wavelength) but they are out of the scope of this chapter.

8. Attenuation Coefficient
 When a signal is applied on a transmission line the strength of the signal is reduced as
the signal travels on the line.
 The secondary line constant which represents the reduction or attenuation in the
voltage or current (or strength) of a signal along the transmission line is called
Attenuation coefficient.
 It is denoted by 𝜶 (Alpha)
 Its unit is Neper/km and it is also, sometimes, measured in dB (Decibels).
 Formula: 𝜶 =
𝐑
𝟐𝐙𝐨
Neper/km
 Where, R = Resistance and
 Zo is Characteristics Impedance of transmission line
 1 Np = 8.686 dB