cst pec touching boundary

Hi
What is the exact difference between "open" and "open (add space)" boundary conditions ?
Anyone can help ?

both boundary condtions use PML (perfectly matched layer). The "add space" enlarges the calculation box automatically for antenna problems, i.e. radiation patterns.

Ok good. Is that mean that I have to specify "open (add space)" for the radiation side(s) ?
I'm simulating simple antenna structures using CST. The antenna is kind of slot or some other shapes as well. Anyway, I'm getting two kind of errors, and I don't know exactly what they means? and why they appear? and how to overcome this problem.
1- Some PEC material is touching the boundry ! This may lead to inaccurate farfield results. Please check your structure.
I have copper not PEC. And it is touching the edge from the port side.
2- Some higher propagation modes at port 1 are not considered in time domain caculations. This possibly leads to an inaccurate energy balance. Consider to reduce port size or decrease the upper frequency limit.

In your structure at the port can propagate some more modes. Try to set more modes in options of port. To problem 1 - It is rather difficult to say something useful without a good illustration.

You should apply "Open (add space)" for radiating directions. Just remember that this is an automatic setting and can be set manually with "Open"+distance of walls under "background properties".
Referring to the error messages:
1. Please check that you are using "Normal" background ("background properties").
2. Use "Open (add space)" for all directions and see if the message reappears.
3. About higher propagating modes - I agree with demonis, and we can help better if you post the model files here.
Good luck,
P.

Thanks a lot for all of you.
Please check the following three structures:
v0: Parallel symmetry planes! No farfield calculation possible.
v1: Some PEC material is touching the boundary! This may lead to inaccurate
farfield results. Please check your structure.
v2: No error messages. No warnings.
So, I like to understand what's going on. What is the wrong with CST?
Regards

About v1: You have no warnings when you set all boundary conditions to open(add space). Otherwise you have not enough space in calcilation domain for precise farfield calculation
PS:
I have also checked vo and v2. In v2 i have the same errors as in vo.
If you want to calculate farfield you must set boundary condition open ( add space)
Are you sure that you use in your structure a right mode of CPW-line?

Thanks a lot.
I know that I have to set "open(add space)" in the radiation sides.
Shall I do that for all sides ? even for x & y ?
Do you mean by CPW mode, that it should be quasi static mode ? or something else ? I think there is no problem in these cases.

You can manually control boundary conditions by settung it in Solve/Background Material/. You can set for x and y directions smaller values as for z direction (only if structure radiates in z direction). If you have a reflector you can set a Zmin smaller as for Zmax.
In you filed you use a mode like in microstrip line. It is also a mode like a slot line (mode 2 for your case, but i am not sure)