Hi,
Am designing SIW with a cut-off of 15 GHz using CST.
in this regard, I have selected RF-Circuits and components-planar filter templates.
designed SIW with microstrip feed. by default template, all directions are electric boundaries. but the result is not good.
if I change the boundaries of Z min and Z max as open, am getting S parameters as I expect(almost at 16 GHz)
Is it correct to have this boundary condition for SIW filter design?
It would be very helpful if you clarify this doubt.
thanks in advance
Where was Zmax, where you were putting a perfect short circuit? Did you have any air above the microstrip or other parts?
@ Malcomm White.
Am attaching the Designed structure. Kindly have a look at it.
Those boundary conditions seem to be what I expect. This is right for a circuit with no lid. You should be able to put a lid on the top - that would be the electric boundary condition. I don't know why that didn't work. Perhaps the top electric boundary was too close to the track (the box isn't high enough), that would make the track look a bit like unbalanced stripline rather than microwave. The lid has to be far enough away from the track so you don't get significant power on top of the microstrip. If not there might be enough propagation between the lid and the track for some power to bypass the SIW and give confusing results, because it would have a different wavelength and so cause ripples in the S21. You could find that out by putting something lossy in the SIW so nothing gets through, or on top of it, where there should be no fields, and see what happens.
Look at the Port mode pattern, and see if the fields go up to the lid (top electric boundary). I think they might.
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