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How can I find eigenmodes propagating in given direction?

Posted Aug 27, 2013, 5:47 a.m. EDT RF & Microwave Engineering Version 4.2, Version 4.2a, Version 4.3, Version 4.3a, Version 4.3b 3 Replies

Vladimir Parfenyev
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Hi!

I have a general question about eigenmode problem in RF module. How can i find only eigenmodes propagating in given direction? For example, let's consider an infinite number of parallel cylinders lying on substrate. I can model such a geometry using pereodic boundary conditions. I would like to find eigenmodes of this system propagating parallel to the substrate and perpendicular to the cylinders. How can i find such a solution?

Thank you in advance!

3 Replies Last Post Aug 30, 2013, 4:32 p.m. EDT
Edgar J. Kaiser Certified Consultant
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Posted: 1 decade ago Aug 27, 2013, 8:11 a.m. EDT
Hi,

so far I havent done too much with EM eigenmodes, but I think they have a k vector. Then the dot product of the mode's k vector and your preferred direction should be a measure for the alignment of the mode.

Cheers
Edgar

--
Edgar J. Kaiser
emPhys Physical Technology
Hi, so far I havent done too much with EM eigenmodes, but I think they have a k vector. Then the dot product of the mode's k vector and your preferred direction should be a measure for the alignment of the mode. Cheers Edgar -- Edgar J. Kaiser emPhys Physical Technology
Vladimir Parfenyev
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Posted: 1 decade ago Aug 27, 2013, 8:35 a.m. EDT
Thank you, Edgar!

But the solver of eigen mode problem doesn't allow to specify a direction of the k-vector of the sought modes (or i don't know how to do it). Of course it is possible first to find all modes and after it one can select desired modes, however such a solution seems irrational. May be someone know how to force the solver look over only the necessary solutions?
Thank you, Edgar! But the solver of eigen mode problem doesn't allow to specify a direction of the k-vector of the sought modes (or i don't know how to do it). Of course it is possible first to find all modes and after it one can select desired modes, however such a solution seems irrational. May be someone know how to force the solver look over only the necessary solutions?
Frank McDermott
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Posted: 1 decade ago Aug 30, 2013, 4:32 p.m. EDT
Use Floquet periodic boundary conditions. Your "unit cell" would be one cylinder diameter wide - the height and width are determined by what you're interested in (see below). By setting the Floquet (Bloch) wavevector (kx,ky,kz under the periodic condition settings) you will determine the solutions you will find.

If your cylinders are infinitely long then the problem is 2D.
If you only care about guided modes than you can also use periodic BCs above and below ensuring that the domain is large enough that the solutions don't couple to each other.

If you do care about leaky modes (into radiation or the substrate ) then use PML above and below.




Use Floquet periodic boundary conditions. Your "unit cell" would be one cylinder diameter wide - the height and width are determined by what you're interested in (see below). By setting the Floquet (Bloch) wavevector (kx,ky,kz under the periodic condition settings) you will determine the solutions you will find. If your cylinders are infinitely long then the problem is 2D. If you only care about guided modes than you can also use periodic BCs above and below ensuring that the domain is large enough that the solutions don't couple to each other. If you do care about leaky modes (into radiation or the substrate ) then use PML above and below.

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