Waveguide filters in CST

Hi All,
My question regards the design and analysis of waveguide (WG) filters in CST.
My main goal is to accurately simulate a combiner of 2 or more WG filters.
I have managed to simulate a single two ports WG filter with the Frequency and the Eigenmode solvers. When I tried to simulate the full structure (more than 3 ports) the results made no sense at all.
I'd appreciate all your comments, and especially about:
1. How accurate is CST in this area of design?
2. Any previous topics about these subjects.
3. What is the recommended CST setup for this type of problem (i.e. solver settings, BC, meshing etc.) ?
Best regards,
P.

CST is a good tool for waveguide filters applications independently of ports number.
I had nice results with Transient Solver. If you want to save time, you can use AR-filter option for TS-settings. For Meshing settings use: Lines per wavelength - 30 and Refine at pec edges by factor - 4...6. Also you can use Adaptive meshing.
At the attachment file you can see example for TS+AR-filter and Frequency and Eigenmode solvers simulation.