thank you snkhan,
I have tested and seen it right!
Actually, when we use a "full plane" wave guide port, we have a Line impedance near of 50 ohm, however, the radiation and total efficiency is very low (only less than 20%)! It is found that these efficiency would be raised with the reducing of port, and the Line impedance is reduced as a results!
Any idea?
Added after 3 hours 12 minutes:
Hi all,
with CST, the simulations in different versions will give different results, is it right?
I checked with the same structure, and same every setting condition, the Line impedances are quite different, i.e, the line impedance in the older version is nearer 50 ohm than the newer one.
Anyway, we should believe the results in the new version, am I right? I know the mesh generation mechanism is usually better in the new version, but the different should be acceptable!
Now, i am trying to get port around 50 ohm value, but it is not easy!
Please have a glance on my design (above). If I use open (add space) in all direction, the simulation become unstable (energy not be converged). Then I used only open boundary at the port location (end of the ground), the simulation is stable, but the far field is noticed is unaccuracy at some low frequencies!
Thanks for your helps!
Added after 46 minutes: