CST Microwave Problem - High reflection problem

Hi everyone,
I have a problem. I am simulating a structure w/ a waveguide port. S11 parameter is linearly higher than 1 when I use open (add) space Boundary condition. Physically not meaningful, energy conservation.
But, when I use open BC, this time I obtain error as:
" Inhomogeneous material at open boundary detected. (The structure must be identical in the open boundary plane and the next two mesh steps. ) "
Can anyone help me w/ this problem.
Thanx in advance.

I have the same question, hope the answers!

Without knowing the specifics of the file I'm guessing, but check these two things:
1. That there is sufficient space between the plane of the waveguide port and the boundary. This error will be generated if the boundary 'touches' (or is within a mesh cell of) the port you are exciting. The 'boundary conditions' dialog lets you insert additional space if required, and
2. That your mesh is sufficiently fine for the structure you are simulating. I've found the default meshing strategy gets it right most of the time but on occassion a manual adjustement can help solve a bunch of cryptic errors and non-physical results! You can amend the mesh globally (or by raising the maximum simulation frequency), or more specifically by right clicking on the desired component in the navigation tree and selecting 'local mesh properties' from the context menu. The maximum mesh steps in all three axes can then be specified in the fields at the bottom of the displayed dialog box. Naturally, increasing the mesh density increases the simulation time though... :)