1_Introduction + EAM Vocabulary + how to navigate in EAM.pdf
ppt-of-waveguide
1. 1
Amity School of Engineering
Waveguide
Conventional transmission lines develop too much loss at
microwave frequencies.
Hollow waveguides present an alternative.
Electromagnetic waves reflect from the walls of the wave guide as
it travels its length.
Brass, aluminum or silver plated.
RECTANGULAR, elliptical and circular
2. 2
Amity School of Engineering
Overview of guided waves in TE, TM and TEM modes.
As frequency increases beyond the lower boundary that has been assigned
as the microwave threshold (1 GHz) conventional R.F. techniques become
less effective.
Lead inductance and capacitance as well as connecting traces on substrates
become issues affecting circuit performance.
An example is TRANSIT TIME.
Physical construction of devices must change.
4. 4
Amity School of Engineering
Waveguide Modes
A waveguide operates most efficiently within modal boundaries.
A given waveguide cross section will have a cutoff frequency where a
signal below it will not propagate.
What type of filter does this act as?
Not all modes strike the walls at the same angle therefore the distance
traveled varies.
This is called multimode propagation.
Effective velocity reduces.
Pulse spreading results and subsequent pulses following closely will
interfere. (Dispersion)
5. 5
Amity School of Engineering
dielectricinwavelengthcutoff
awherea
c
c
=
==
λ
λ
dimensionlong
2
a
c
c
c
cc
c
f
f
c
a
f
c
f
c
a
2
2
2
=
=
=== λλλ
6. 6
Amity School of Engineering
Modes of propagation
10TE
# of variations along b
# of half cycles along a
9. 9
Amity School of Engineering
22
1
2
1
−=
−=
f
f
c
a
cv c
g
λ
Group velocity- used to determine the length of time a signal takes
to travel the length of the waveguide.
11. 11
Amity School of Engineering
22
1
2
1
−
=
−
=
f
f
c
a
c
v
c
p
λ
12. 12
Amity School of EngineeringImpedance of a waveguide.
2
1
377
−
=
f
f
Z
c
O
13. 13
Amity School of Engineering
The calculation for wavelength in a
guide requires phase velocity.
22
1
2
1
−
=
−
=
=
f
fc
a
or
f
v
g
p
g
λ
λ
λ
λ
λ
