[SOLVED] Number of modes for microstrip inside of cavity

[niccoh]

I need to simulate a microstrip to microstrip (different substrates) transitions which lie inside a metal cavity.

See (b)



[found at mwrf . com / site-files / mwrf .com /files /archive /mwrf .com /Files /30 /19725 /fig_02 .gif]

The cavity cross-section is about a square.

When I simulate by setting the wave ports to the cavity face at the input and output of the trace I get the warning that multiple modes are propagating at these gamma values... I still converge and get my sweep for an S11/S21 measurement. When I go back and set the number of modes of the wave port to identify and simulate all those modes I get a different result for dominant mode when looking at S11/S21.



How do I know which one I should go with? This structure is fed by a coax a little before which has only 1 mode propagation but I don't want to have to model that aswell as that's more computations.

Thank you

 

[PlanarMetamaterials]

The latest version of HFSS seems to enjoy doing this for no particular reason. It will tell you that there are additional supported modes, even if they are modes like the TM10 surface-wave mode, and not necessarily TEM.

I would ignore it if you are only exiting one TEM mode.

 

[niccoh]

Yes there's two that look to be just your standard TE10 waveguide mode just once each side length of the port is large enough to support it. This will be excited by a TEM mode from a coax I just didn't want to have to simulate that.

Thank you!