28-11-2012, 03:47 PM
Advanced Electromagnetism
AdvancedElectromagnetism-Part6.pdf (Size: 1.81 MB / Downloads: 333)
Transmission lines are used (as are waveguides) to guide
electromagnetic waves from one place to another. A coaxial
cable (used, for example, to connect a radio or television to an
aerial) is an example of a transmission line.
Transmission lines may be less bulky and less expensive than
waveguides; but they generally have higher losses, so are more
appropriate for carrying low-power signals over short distances.
Advanced Electromagnetism 1 Part 6: Transmission Lines
Transmission Lines
In this part of the course, we shall consider:
• a simple LC model of a general transmission line;
• the speed of propagation of a wave in a transmission line;
• the characteristic impedance of a transmission line;
• impedance matching at the termination of a transmission
line;
• practical transmission lines (parallel wires; coaxial cable).
Voltage Standing Wave Ratio
At any given time, the voltage varies sinusoidally with position
along the transmission line.
But the amplitude of the variation varies (with time) from
1 − |K| to 1+|K|.
The voltage standing wave ratio (VSWR) is defined as the
ratio of the maximum to the minimum voltage amplitude: