Waveguide

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A hollow metallic table of uniform cross section for transmitting electromagnetic waves by successive reflections from the inner walls of the tube is called waveguide.

Difference between Transmission line & waveguide
Transmission lineWaveguide

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2)Two or more conductors separated by some insulating medium (two wire, coaxial, etc)2)Hollow metallic conductors or tube of uniform cross section for transmitting electromagnetic waves by successive reflections fro inner walls of the tube.
3) Normal operating mode is TEM or quasi-TEM mode3) Operating modes are TE or TM modes
4)No cut-off frequency for TEM mode4) Must operate the waveguide at a frequency above the respective TE or TM mode cut-off frequency
5) All frequency can be transmitted5)Only higher frequency i.e frequency ≥ cut-off frequency
6) Signal attenuation at higher frequencies due to conductor & dielectric losses6) Lower signal attenuation at high frequencies
7)Small cross sectional transmission lines (like coaxial) can only transmit low power levels due to relatively high fields concentrated at specific locations within the device7)Metal waveguides can transmit high power levels. The fields of the propagating wave are spread more uniformly over a larger cross sectional area than the small cross section transmission line
8) Large cross-section transmission lines can transmit high power levels8) Large cross-section(low frequency) waveguides are impractical due to large size & cost

Similarities:-

1)Wave travelling in a waveguide has a phase velocity & will be attenuated as in a transmission line.

2) When the wave reaches the end of the waveguide, it is reflected lineless. The load impedance is adjusted to absorb the wave.

3) Any irregularity in a waveguide produces reflection just like an irregularity in a transmission line

4) Reflected wave can be eliminated by proper impedance matching in a transmission line.

5)When both incident & reflected waves are present in a waveguide, a standing wave pattern results as in a transmission line.

Types of waveguides

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Circular waveguide:- It tends to twist the waves as these travel through them.

Difference between TE and TM mode

TE ModeTM Mode
1)Electric field is transverse to the direction of propogation1)Magnetic field is transverse to the direction of propogation
2)No electric line is in direction of propogation i.e Ez=02)No magnetic line is in direction of propogation i.e Hz=0
3)Magnetic line is not purely transverse to direction of propogation i.e Hz≠03)Electric line is not purely transverse to direction of propogation i.e Ez≠0
4)TE10 is the dominant mode4)TM11 is the dominant mode
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Created by Vishal E on 2017/08/04 13:03