Parallel Plate Waveguide Loss Dependence On Mode

[fred3142]

Hi,

The attenuation resulting from puting a signal into a parallel plate waveguide is dependent on the excited mode. Why does the TM mode have greater attenuation than the TE mode? I can see in the maths it 'works out' to be that, but what would be a more conceptual/physical reason?

Is the TM mode in contact with the boundary more than the TE mode This image seems to indicate that there is more electric field touching the conductor in TM polarisation, so my guess is that this would cause the greater conductor loss (because there would be a larger evanescent field in that would be lost in the conductor).

loss.png shows the attenuation curves for various modes (the image is from the textbook by Pozart).

Thanks.

 

[eljose79]

Hi there,

That's a great question! The reason why the TM mode has greater attenuation than the TE mode in a parallel plate waveguide is due to the difference in their electric field distributions. In the TM mode, the electric field is perpendicular to the direction of propagation and parallel to the plates, which means that it has a larger component in contact with the conductor. This results in a larger evanescent field that is lost in the conductor, leading to greater attenuation.

On the other hand, in the TE mode, the electric field is parallel to the direction of propagation and perpendicular to the plates, which means that it has a smaller component in contact with the conductor. This results in a smaller evanescent field and therefore, less attenuation.

So, in summary, the TM mode has greater attenuation because it has a larger evanescent field in contact with the conductor due to the orientation of its electric field. I hope this helps to provide a more conceptual understanding of the difference in attenuation between the two modes.

Thank you for sharing the attenuation curves from the textbook by Pozart. It's always helpful to have visual aids when discussing technical concepts. Let me know if you have any other questions or if you need further clarification.