Hi antenna_beginner, I am a beginner too. I am working on HFSS not CST, but i believe the design should be same even with different softwares. In Coaxial/Probe feeding technique we subtract or remove a circular slot from ground plane and create 3 cylinders(probe, pin, coax) and a circle(waveport) but i am sure about making patch+inner cylinder and ground+outer cylinder as one object each.
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Follow below clip on youtube to understand better:
https://youtu.be/ntPqoZ2NI90