Upload
channing-snow
View
71
Download
2
Tags:
Embed Size (px)
DESCRIPTION
Waves and Transmission Lines. Wang C. Ng. Traveling Waves. Envelop of a Standing Wave. Load. Waves in a transmission line. Electrical energy is transmitted as waves in a transmission line. Waves travel from the generator to the load (incident wave). - PowerPoint PPT Presentation
Citation preview
Waves in a transmission line
• Electrical energy is transmitted as waves in a transmission line.
• Waves travel from the generator to the load (incident wave).
• If the resistance of the load does not match the characteristic impedance of the transmission line, part of the energy will be reflected back toward the generator. This is called the reflected wave
Reflection coefficient
• The ratio of the amplitude of the incident
wave (v+ ) and the amplitude the reflective
wave (v-) is called the reflection coefficient:
v
v
Reflection coefficient
• The reflection coefficient can be determine from the load impedance and the characteristic impedance of the line:
0
0
ZZ
ZZ
L
L
Resistive Load
• ZL = 0.5 Z0
= - 1/3
• v - = -0.333 v + at the load
• As a result, vL = v + + v - = 0.667 v +
Resistive Load
• ZL = 2 Z0
= + 1/3
• v - = 0.333 v + at the load
• As a result, vL = v + + v - = 1.333 v +
Reactive Load (Inductive)
• ZL = j Z0
= + j1
• v - = v +90 at the load
• As a result, vL = v + + v - = (1 + j1) v +
= 1.414 v +45
Reactive Load (Capacitive)
• ZL = -j Z0
= - j1
• v - = v +-90 at the load
• As a result, vL = v + + v - = (1 - j1) v +
= 1.414 v +-45
-j2
-j4
-j1
-j0.5
j0.5
j1
j4
j2
j0 0 0.5 1 2 4
zL = 1 + j 2
0.7 45
45
0
135
90
180
225
270
315
zL 1 j 2
zL 1
zL 1
0.5 0.5i
0.707
arg 45deg
-j2
-j4
-j1
-j0.5
j0.5
j1
j4
j2
j0 0 0.5 1 2 4
zL = 0.5- j 0.5 0.45 -120
45
0
135
90
180
225
270
315
zL 0.5 j 0.5
zL 1
zL 1
0.2 0.4i
0.447
arg 116.565 deg