Dear Muhammmed Ali Işık ,

As a proposal you can use regular polygons instead of a circle. Then you can use rectangular waveguides.

Best wishes

See this question

https://www.researchgate.net/post/How_to_simulate_circular_array_of_antennas_in_CST#view=60004fdfe0a06e2d3b71c9c4

You can try using discrete port in place of waveguide port. Less picky in terms of alignment to Cartesian planes.

Dear Muhammmed Ali Işık ,

As a proposal you can use regular polygons instead of a circle. Then you can use rectangular waveguides.

Best wishes

https://www.edaboard.com/threads/wave-plane-or-waveguide-port-in-cst.57307/

https://iopscience.iop.org/article/10.1088/1742-6596/1402/4/044032/pdf

Md Nazmul Hasan thank u so much for the answer. But i think my question was not clear. So let me explain better. I wanna desing an array in circular form, like microstrip antennas placed as 45 degree angle around an object. I insert the picture of the system. But whenever i tried this, CST always gives me the error i mentioned above. Strangely when i placed the antennas in 90 degree angle, then system works without error. Do u have any idea why?

PS: i watched most of your videos already, they are so helpful :)

Your question was perfectly clear. Some of the answers are wrong.

Waveguide ports in CST have to be parallel to the x, y or z planes. If they are rectangular, the sides also have to be parallel to one of the axes. If you want to use waveguide ports and the places you want them aren't parallel to any of these you have to follow these rules to get a port then and bend and/or twist the transmission line round to where you want your feed to be.