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waveguide and single modes
Posted 05.04.2011, 01:24 GMT-4 RF & Microwave Engineering 1 Reply
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I'm doing electromagnetic wave propagation in 3D waveguides. My question is how to get single modes? Not just the fundamental mode, but also higher order modes like TE_11, TE_21, and etc.
In my rectangular 3d waveguide, I use frequency domain study and specify TE_11 at the ports. But for frequencies just above the cut off of TE_11 and below the next mode, I get E-field distribution that looks like it's a combination of modes, definitely doesn't look like single mode distribution. I wonder why this would happen ? My guess is it is because frequencies above cut frequency of TE_11 allows other lower order modes too.
But there must be some way to get single modes of higher order in COMSOL right? Can you please tell how to get this right?
Thank you so much! I appreciate it!
Tina Huang
Hello Yuting Huang
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I noticed the same thing when I was recently simulating waveguide modes for teaching and visualization purposes. TE_mn modes just don't look realistic, for instance, from an arrow volume -plot you can see that the E-field has a longitudinal component. The TM-modes, on the other hand, look much better.
Supposedly, this might relate to a numerical coupling between TE and TM modes, as in FEM, the solution is based on minimizing the error with respect to the energy, and the actual field valus may not be that accurate. Or then there just is something wrong with the TE excitation.
Also, with Comsol 4.1, I was not even able to simulate the ports with TM modes at all, it always ended up with an error. Now, with 4.2, the TM ports seem to work as well.