3. At frequencies higher than 3 GHz, transmission of
electromagnetic energy along the transmission lines
and cables becomes difficult.
This is due to the losses that occur both in the solid
dielectric needed to support the conductor and in the
conductors themselves.
SOLUTION
A metallic tube can be used to transmit
electromagnetic wave at the above frequencies
4. Waveguides are basically a device ("a guide") for
transporting electromagnetic energy from one region
to another
The electric and magnetic fields associated with the
signal bounce off the inside walls back and forth as it
progresses down the waveguide
The waveguide acts as a high pass filter in that most
of the energy above a certain frequency (the cutoff
frequency) will pass through the waveguide, whereas
most of the energy that is below the cutoff frequency
will be attenuated by the waveguide.
7. The size of the waveguide determines its
operating frequency range.
The frequency of operation is determined by the
dimension ‘a’.
This dimension is usually made equal to one –
half the wavelength at the lowest frequency of
operation, this frequency is known as the
waveguide cutoff frequency.
At the cutoff frequency and below, the
waveguide will not transmit energy. At
frequencies above the cutoff frequency, the
waveguide will propagate energy.
8. Angle of incidence(A) Angle of reflection (B)
(A = B)
(a)At high
frequency
(b) At medium
frequency
( c ) At low
frequency
(d) At cutoff
frequency
9. There are various type of mode, but rectangular wave
guide work in TE mode.
The general symbol of representation will be
TE m, n where the subscript m indicates the number
of half wave variations of the electric field intensity
along the ‘a’ ( wide) dimension of the waveguide.
The second subscript n indicates the number of half
wave variations of the electric field in the ‘b’ (narrow)
dimension of the guide.
The TE 1, 0 mode has the longest operating wavelength
and is designated as the dominant mode. It is the mode
for the lowest frequency that can be propagated in a
waveguide.
Dominant mode: the mode with lowest frequency
10. For a standard rectangular waveguide, the cutoff
frequency is given by
22
2
1
b
n
a
m
f c
11. Dark side:
Physical size is the primary lower-frequency limitation of waveguides. The
width of a wave guide must be approximately a half wavelength at the
frequency of the wave to be transported. For example, a waveguide for use at
1 megahertz would be about 500 feet wide. This makes the use of
waveguides at frequencies below 1000 megahertz increasingly impractical.
The lower frequency range of any system using waveguides is limited by the
physical dimensions of the waveguides.
Waveguides are difficult to install because of their rigid, hollow-pipe shape.
costly
BRIGHT SIDE:
Minimum loss of power in case of waveguide
Power handling capability is 10 times than coaxial cable
HIGH frequency signal are easily transported.
12. Consider a rectangular wave guide with transverse
dimension 2m*1m driven with an angular
frequency f=109 rad/s. Which transverse electric
(TE) modes will propagate in the wave guide ?
(NET-JUNE 2015)
(A) TE10 ,TE01 and TE20
(B) TE10 ,TE11 and TE20
(C) TE01 ,TE10 and TE11
(D) TE01 ,TE10 and TE22
