Course Notes for EE1266 Applications of fields and waves
Chapter 1: Lecture 1
1
NOTES for Transmission Lines I
This lecture covers Chapter 2.1 to 2.4
1. Transmission lines (T-lines), wavelength,
propagation mode
2. Lumped-element model
3. Telegrapher’s equation and solution
1. Transmission lines, wavelength, and TEM wave
• Transmission lines are a carrier to transmit transverse EM
waves (or other waves in general). T-line connects
generator circuits (GC) to loads. And yes, transverse EM
(TEM) wave is a special EM wave, which will be defined
below.
• When do we need to consider a “line” to be T-line? Well,
when the wavelength of TEM waves is comparable or
smaller than length of “the line”, then you will need the
knowledge you learn here, because “the line” becomes a
T-line. Just give a few rough examples
o A coaxial cable of 1 m is just “a line” if it transmits
signal with frequency of 1 MHz. Because the
wavelength of the TEM wave at this frequency is c/f~
100-300 meter (the speed of the light is smaller than
300 M meter/s). However when the signal has
frequency of 1 GHz, “this line” becomes a T-line
because the wavelength of the EM wave is <0.3 meter,
therefore the voltage along the line varies along “the
line”.
o Conducting wires on a CPU chip can be a few meter
long. They are just “a line” when clock frequency is
~10 MHz (20 years ago). They becomes T-lines today
because CPU runs 3 GHz clock.
• Below are some examples of T-line, apparently, no all the
line can be consider as T-line. Strictly speaking, only
structures support TEM waves can be considered as T-
lines. Because the E-filed starts from one conducting plate
Course Notes for EE1266 Applications of fields and waves
Chapter 1: Lecture 1
2
and end at the other one, which the voltage between two
conducting plates are well-defined, and we can use
lumped-element model to describe the structures (R. L, C
circuits).
2. Lumped-element model
Beca