A thought on waveguides(TEM mode)

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vig
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I have been wondering about the physical reason why a TE wave that goes STRAIGHT through the waveguide(without any reflections) can't propagate and would like some one to clarify the same
OK..so if i consider a UNIFORM PLANE TE WAVE that goes straight thorough, then by definition of uniform plane wave, the amplitudes across the wavefront must be constant. But, as the wavefront approaches the plates, the amplitude of the E and H field both go down to zero. Thus, the only solution being that the amplitude of E (and H) are uniformly zero.

However, for a wave that is oblique to the surface, the wave STRIKES the walls of the metallic plates, implying that a REFLECTED field is generated to make the resultant field on the conductor is zero, implying that the wavefront of the OBLIQUE wave CAN have equal amplitude throughout..

It would be great if someone clarifies this understanding!
Thank you!
P.S: I have gone through the mathematical derivations, but just tried to explain it physically with my limited knowledge...
 

Answers and Replies

  • #2
marcusl
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A TE mode wave will propagate down a waveguide, unless it is beyond cutoff. There is a way of visualizing a propagating wave as a superposition of two plane waves that zigzag down the guide. Is this construction that you are looking at?
 
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  • #3
Claude Bile
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You can describe any waveguide mode as an infinite sum of monochromatic, uniform plane waves propagating at different angles via the principle of superposition.

The "angular spectrum" (plane wave amplitude vs propagation angle) is related to the amplitude distribution of the waveguide mode via a Fourier transform.

Does that clarify things?

Claude.
 
  • #4
vig
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A TE mode wave will propagate down a waveguide, unless it is beyond cutoff. There is a way of visualizing a propagating wave as a superposition of two plane waves that zigzag down the guide. Is this construction that you are looking at?
Thanks for the reply..I know TE modes propagate..What I meant was a TE wave that goes STRAIGHT through...so it essentially is a TEM wave with Electric field being transverse to the direction of propagation....
 
  • #5
marcusl
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First of all, TE and TM waves do propagate down the guide. I assume that's what you mean by "straight through"--after all, there's no other way down a waveguide than straight. Second, TEM modes do not exist in a waveguide. They require a center conductor such as in coax cable.
 

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