cst multipin port

Anyone can give me an example of simulation in CST of a coplanar microwave circuit? So I can see how to setup the ports

Thanks

Hi,

just check the branch line coupler in the MWS examples. They use Multipin port with several current sets. You can do the same with your coupler.

F.

Thank you for your advice.... I opened the lange coupler in the CST example directory but I've seen that the port are simple and not multipin... Which one are correct? Multipin Waveguide ports or simple Waveguide ports?

Hi.

depends.. If the signal line are rather far away from each other, you can assign one port for each line. Make sure that the ports do not overlap.
If the line are closer to each other you can use a multipin port with several current sets instead.

F.

Here you can find the structure that I posted in another Discussion on this forum, can you tell me if the port setup is correct? Thank you!:

h**p://www.edaboard.com/download.php?id=103698

The discussion is on:

h**p://www.edaboard.com/ftopic82440.html

Hi,

you you just posted the geometry (*.mod and *.par) file. The download just contains a picture.

F.

Here you can find the entire CST project, when I simulate this structure I find incorrect results (I find that the ports are shorted) can you help me to set correctly the simulation?

Thank you

Hi,

I had a quick look at your structure. The Vias in your model are Vacuum. Are you sure this is correct? Furthermore the Ports 2 & 3 are directly located at a GND bridge. Because the GND bridges are not connected with the main GND (vias problem) the port mode solvers sees some "floating" metal plates right at the port. Please change this. Finally, I would move the ports 2 & 3 away from the bridges anyway. If the bridge is finally connected the port mode solver will calculate a mode which includes the bridges. This will certainly vary from your CPW mode. Whenever you have something like this it should be INSIDE the structure and not right at the port.

F.

You're right, the via must be conductive but the bridges, if you zoom the structure are not connected with the port... Do you think that the multipin ports are correct?

Hi,

I still would move the ports away by extending the CPW. You will get higher order modes at the bridge and these modes should not be to close to the ports.

Your dimensions are not correct. Currently the coupler is about 1m in size! The Port definition in general should be O.K. when you corrected all this. Just check the impedance of the correcte modle. What impedace you you expect?

F.

I corrected the dimensions of the project ( um ) but I don't understand why the bridges make higher order modes? Can you explain me please?

Hi!

this can be explained using a simple coax step. Far away from the step, I have a very nice TEM field pattern. When you get very close to the step, the field pattern changes because of the field disturbance generated by the step. The results field can consider being a sum of all the higher order coax modes. These modes can usually not propagate thru the coax because they are bellow cut-off. They are just present near the step.

By the way: this is how Mode Matching programs work. They find the weight coefficients for the higher order modes at both sides of the step...

In your CPW you will have the same effect. Around the GND bridges, the field pattern has to change to fulfil all boundary conditions given by the geometry. These changes are local and they can not propagate. However the WG port does not like these "disturbances" right at the port because the port tries "per definition" to excite the Structure with a pure mode.

This is why it makes sense to have the port somewhat away from the next discontinuity


F.

thx for your infomation

it's helpful for me

hello all.pleas tell me how i open .dsn