differential microstrip waveguide

Hi seniors,

I would like to simulate a differential microstrip line, and the waveguide port with multipin port is used. However, The line impedance can not be simulated correctly. Most of my simulation result are 85ohms of 100ohms geometry. Could someone provide any suggestion?

BTW, simulation file is attached.

Thanks![/b]

Hi yhchen,
welcome to the forum,

I have a couple of questions:
1. Did you calculate the desired parameters for your line?
2. Did you get the theoretical desired impedance?

If you did so, then the problem with your design is Mesh-related.
Your model shows very thin meshing in the port area- especially in the line area.
My suggestions:
a. Increase mesh density in the line area. The transverse mesh cells sholud be about h_substrate/4.
b. Decrease the port size - about 8x(line width) X 5x(h_substrate).
c.Boundaries for the surrounding box can be Electric - reduces calculation time.

Good luck,
P.

Hi P.,

Thanks
All parameters that I set in CST are calculated for 100ohm differential line, but the simulation result is different from desired.

The port size was decreased and boundaries were changed to Electric. However, I can not increase transverse mesh density by increasing "Lines per wavelength" or "Lower mesh limit".

yhc

Select the desired component -> right click -> mesh properties -> and then set the mesh density of the desired component.
If the mesh doesn't change, increase the "lower mesh limit". I do not recommend modifying "lines per wavelength" for this kind of problem.

Regards,
P.

Thanks a lot!
However, I still can not get calculated impednace from CST.