# Help me visualize TE/TM modes

1. Mar 14, 2013

### dexterdev

Hello PF,

I have a doubt. polarization refers to the plane of Electric field right?, then linearly polarized wave is TEM and circularly may be TE/TM right? Please someone clear my doubt...

-Devanand T

2. Mar 15, 2013

### the_emi_guy

Polarization is generally associated with TEM waves and is often (if not mostly) the relationship between the E-field direction and the horizon. Polarization can be shifted from horizontal to vertical, for example, by simply rotating an antenna.

The TE and TM modes inside of waveguides are a different story. The orientations of the fields are governed by the dimensions of the waveguide and the particular mode. I cannot rotate an antenna inside of a waveguide and change the polarization of the internal fields like you can with TEM waves in free space. I can rotate the entire waveguide and the internal fields will have rotated relative to the the external horizon but this is of no interest.

Very briefly...

TE and TM occur when waves are guided (rectangular microwave waveguide, fiber optic cable).
TE means that the E-field is always orthogonal to the direction of propagation (often called z-axis of guide). H-field will have a component along z-axis.

TM means that the H-field is always orthogonal to z-axis (making closed loops in x-y axis). E-field will have component along z-axis.

The mode is analogous to the vibrational modes on a violin string. The string has a node at each end that prevents movement. The lowest frequency mode has the string motion maximum in the center between the nodes. The next mode has a node in the center of the string and maximum amplitude at the 1/4 and 3/4 points, and is at twice the frequency.

In a waveguide there are two mode indices (m,n) because there are two dimensions involved.

Do Google searching for images of modes within rectangular waveguide. Pictures really help understanding this.

3. Mar 15, 2013

### dlgoff

I google searched "em modes". Here's the first hit on my list. I don't think you'll find a much better explanation IMO.

"whites.sdsmt.edu/classes/ee481/notes/481Lecture10.pdf" [Broken]

Last edited by a moderator: May 6, 2017
4. Mar 15, 2013

### dexterdev

Thank you for the help...