Slides For Emf

Transmission concepts understand the concept

line

Two of Transmission line student should know the answer of this question Q - What is a transmission line and how does it differ from the general electrical circuit? •The answer is that any two conductors between which voltage is applied can be considered to be a transmission line • •In general , there is no clear - cut distinction between the usual concept of a circuit and a transmission line except for extreme cases with usual circuits on one end and transmission lines on the other •Fortunately , many applications fall into one of these extreme cases , but this is occurring less and less as advances are being made in high - speed

Power Frequency (f) is @ 60 Hz

Wavelength (λ ) is 5 106 m ( Over 3,100 Miles)

Trans missio n Line

Power Plant

Could be considered as Transmission Line?

Consumer Home

Transmission Lines Class 6

•If the cables are suspended in air then the power will transferred at the speed of velocity of light i . e 186000 miles / second •There is a potential difference along the wire itself as a result of finite time required to reach the point B •whether or not a line is to be considered as a transmission line depends on both the length of the line and the frequency of the applied voltage or , more specifically , it depends on the ratio of the length of line to the wavelength of the

When does a L-line become a TLine?

§Whether it is a

bump or a mountain depends on the ratio of its size (tline) to the size of the vehicle (signal wavelength)

When do we need to use transmission line analysis techniques vs. lumped circuit analysis?

§Similarly, whether or

Wavelength/edge rate

Transmission Lines Class 6

Tline

not a line is to be considered as a transmission line depends on the ratio of length of the line (delay) to the wavelength of the applied frequency or the rise/fall edge of the signal

Key point about transmission line operation Voltage and current on a transmission line is a function of both time and position . I I

V = f ( z, t ) I = f ( z, t )

2

1

To infinite V1

V2

To infinite dz

• The major deviation from circuit theory with transmission line , distributed networks is this positional dependence of voltage and current ! • Must think in terms of position and time to understand transmission line behavior Transmission Lines Class 6

Tra n sm issio n lin e e q u iv a le n t circu its H I +∆I I I I +∆I +

+

+ +

E V I

-

-

-

-

V +∆V I +∆I

V I

H

V +∆V I +∆I

•Both Electric and Magnetic fields are present in the transmission lines – These fields are perpendicular to each other and to the direction of wave propagation for TEM mode waves, which is the simplest mode •Electric field is established by a potential difference between two conductors . –Implies equivalent circuit model must contain capacitor. •Magnetic field induced by current flowing on the line –Implies equivalent circuit model must contain inductor.

•A transmission line can be represented as the cascade networks ( subsections ) of these equivalent models • •The total impedance can be obtained as the series impedance of subsections

Ideal transmission lines lL lC

•Ideal ( lossless ) Characteristics of Transmission Line –Ideal TL assumes: •Uniform line •Perfect (lossless) conductor (R0 0) •Perfect (lossless) dielectric (G0 0)

Electromagnetic

waves

Electromagnetic radiation is a form of transmitted energy . Electromagnetic radiation is so-named because it has electric and magnetic fields that simultaneously oscillate in planes mutually perpendicular to each other and to the direction of propagation through space.

Polarizatio is n the distribution

•Polarization of the electric field in the plane normal to the propagation direction. • •It is a property of waves that describes the orientation of their oscillations.

Linear Polarization electrodynamics , linear polarization

In or plane polarization of electromagnetic radiation is a confinement of the electric field vector or magnetic field vector to a given plane along the direction of propagation

Circular polarization In electrodynamics, circular polarization of electromagnetic radiation is a polarization such that the tip of the electric field vector, at a fixed point in space, describes a circle as time progresses.

Right circular

•It is a special case of more general type called Elliptical polarization

Left circular

Elliptical polarization polarization is the

Elliptical polarization of electromagnetic radiation such that the tip of the electric field vector describes an ellipse in any fixed plane intersecting, and normal to, the direction of propagation.

Polarization Ellipse y E2 E b a

 E1

x

•At a fixed value of “ Z “ the electric vector E rotates as a function of time, and the ellipse described by the tip of the vector is called as a polarization ellipse.

Consider a light ray with an instantaneous E-vector as shown r E ( ω,t ) = xE x (ω ,t )+ yE y ω( ,t

y

Ey x

)

Ex =E 1 sin(− tω β z )

Ex

E y =E E1 in E2 in δ

2

sin(− tω + β z δ)

is the amplitude of wave linearly polarized x direction is the amplitude of wave linearly polarized y direction is the time-phase angel by which Ey leads Ex