SMA cable connected to cavity not simulating properly in CST

Hi, I have a problem with my simulation in CST where I have a rectangular cavity with a simple SMA opening as a set of coaxial cylinders with dimensions I have checked to make 50 Ohms.

I intend to simulate the resonance of EM waves entering the cavity and I calculated the dimensions of the cavity to fit resonance of around 2 GHz, but when simulated, the cutoff frequency of the port (defined to be the plane entering the coax cables) to be way above 2 GHz (18 GHz?) and the cutoff frequency does not depend on the cavity's dimensions but the SMA opening's size.

Also the Zwave does not seem to be 50 Ohms anymore.

Any tips on how to design such a cavity + SMA opening?

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