Transmission lines carry various signals such as telephone, computer data, TV and telegraph. They have a characteristic impedance that is the ratio of voltage to current. If the voltage and current ratios are equal at the input and output of a transmission line, it has perfect performance. The propagation constant describes the attenuation and phase change of signals as they propagate along the transmission line. It is made up of the attenuation constant, which determines the magnitude ratio between the input and output, and the phase constant.

1. UNIT I TRANSMISSION LINE THEORY
General theory of Transmission lines
D.Gopinath AP/ECE
Ramco Institute of technology
Academic year (2017-18 Odd)

4. Transmission Line in communication carry
1)Telephone signals
2)Computer data in LAN
3)TV signals in cable TV network
4)Telegraph signals
5)Antenna to transmitter link

10.  Characteristic impedance, Zo
◦Ratio of voltage to current, V/I = Z
◦From transmission line model
CjG
LjR
Zo




11. currentOutput
currentInput
ePerformanc 
If the ratios of voltage to current at input and
output of the network are equal then
2
1
2
1
V
V
I
I


12.  The magnitude ratio does not express the complete
network performance , the phase angle between the
currents being needed as well.
 The use of exponential can be extended to include the
phasor current ratio.
N
e
I
I
V
V

2
1
2
1

13. Hence
 j
 j
ee
I
I 

2
1
If  A
I
I
2
1

e
I
I
A 
2
1 
 j
e

14.  The term γ has been given the name propagation
constant
 =attenuation constant, it determines the
magnitude ratio between input and output quantities.
 It is the attenuation produced in passing the network.
 Units of attenuation is nepers

e
V
V

2
1


15. 

16. TEXT BOOKS
 1. John D Ryder, “Networks, lines and fields”, 2nd
Edition, Prentice Hall India, 2010.
REFERENCES
 E.C.Jordan and K.G. Balmain, ―Electromagnetic
Waves and Radiating Systems‖
 Prentice Hall of India, 2006.
 G.S.N Raju "Electromagnetic Field Theory and
Transmission Lines‖ Pearson
 Education, First edition 2005.