waveguide port cst stability
@itzikhaim
Hello,
ok may be we can work it out.
You got exactly my problem. Too large size enables higher order modes (hollow waveguide modes) to propagate. Too low size decreases the accuracy of the calculated s-matrix and sometimes results in stability problems, because the energy cannot leave the calc. room.
Anyway, I do only excite mode 1, which is the QTEM mode of the microstrip in my case. DOES THE W.PORT ALREADY BRING THE TE-MODE or DOES THE TE-MODE DEVELOP WITHIN MY CIRCUIT. I would understand the last.
The next problem is to determine, when the higher order mode becomes propagatable. I use the 2D frequency domain eigenmode solver of the waveguide port. If I reduce the size, there is critical size, where all higher order modes are described with an -40dB distance. So I know they are decreasing.
But the -40dB distance is sometimes longer than my circuit dimensions. Means, if these modes develop, they would be there. ???
The next problem is, within coplanar waveguid structures, there are some natural higher order modes. We should consider them. But just considering them and not exciting them, makes it impossible to extract a Touchstone file or even to Renormalize the S-Matrix.
My solution to this problem for now, is to use the MUR-Boundary on the port.
Means special solver setting: Absorb unconsidered modes at port.
So you can only consider mode one, but the other modes are also absorbed.
This topic is very important to me.
So if anybody has any comments, please write it.
Thanks to itzikhaim for reply.