Design of a 50 ohms balun on CST

Hi everyone
I would like to design a 50 ohms balun on CST and also simulate it. I tried designing one but after simulation it says 'the distance between the element 1 and waveguide port is small. Must be at least three mesh steps'. Advice pls

First advice: Increase the mesh density
Second advice: Post a pic of your simulation structure. It's easier to help.

The highest meshcells is 300,000. Where do I increase the mesh density. The attached file is the design of the balun. I just have a feeling the design is wrong. Thank you

Can you post a better pic of your structure? You can change the mesh density in "Global mesh settings".

Is this clear enough?

Ok, increase the mesh density or try to become familar with adaptive meshing and local mesh setup. You can check your settings with the mesh view.

I will try it. Do you think I should fix another lumped element at the spiral antenna point that is create a point P1 and P2. Because the 50 ohms is feeding into an antenna with an impedance of 183 ohms.

You're using some coaxial feed for your antenna?

Yes. But I read somewhere, it was suggested to use a tapered balun for the antenna. I do not know anything about balun or how it is designed. Coaxial balun looked liked the easy one to design.So confused.

Maybe try for first examination a discrete port.

Ok I will try it then reply on how it went. Thanks

@ johnjoe Had to change the design of the balun for a S-band spiral antenna. The issue now is getting the accurate calculation for the design. I am using a journal 'A printed circuit balun for use with spiral antennas' to get the dimension but can't figure it out. Help plssssssss