How to define CPW in CST MWS ?

what is the best way to draw a waveguide port (coplanar waveguide) for antenna feeding in CST ?
should i draw a box extruding from the substrate's surface or can i define the port's face directly on the substrate's face ?
i ve tried the first option but my result is totally different from the designer's. either the reflection is very high or there is so much riple.

Hi abti,
highlight the centre conductor and extend the port in the z and (x/y) direction by an amount enough for the port modes to propagate, (also enclosing part of ground). If it is an antenna, use all open boundary. Run once and if there are ripples in return loss, active AR filter in the next run.
Hope this helps.
Element7k

Hi Element7k,
thanx a lot. that really helps. i chose electric boundary for Zmin and that was the mistake. now i got the line impedance calculated.
but now i m having a problem in farfield. the solver said that some PEC material touches the boundary which can lead to inaccurate farfield result. the thing is i didn't even define any PEC material in my structure. ( i chose open boundary for all but for Zmax i put open boundary add space- because of the farfield).
(i wanted to attach my model, but the file mod is not allowed here)

Hi abti,
pls zip up ur project by using macro --> file. Then do the upload please. Maybe check your backgnd material.
Cheers,
Element7k

Hi Element7k,
the pc i'm working on CST broke down and they still couldn't fix it. So i am now working on unix with HFSS. Can i send u a private message if i need any help with CST once the pc is ok ?

for my opinion, pick the edges points and the center point of the ground plane then choose WG port

Hello,
I'm using CST v.5. I tried to simulate simple structure. It is CPW ended with slot antenna. I have ground metal as well.
I've defined the waveguide port as six times the feeder width.
The line impedance in 2-D result is only 14 Ohm. It should be around 60 Ohm.
Any help please.