Answer
When 'CAL – Start Cal – Calibration unit' is selected, the firmware automatically detects which port of
the VNA is connected to which port of the cal unit. If an attenuator of 10 dB or higher is inserted, then
that port cannot be detected and it is therefore not put on the list. But it can be inserted manually:
Select "Modify Calibration Settings". Another window will open.
Set the check mark next to the missing port.
--> An error message appears: "Each VNA test port to be calibrated requires an unambiguously
assigned cal unit port"
--> The missing port has been added to the "Port Assignment" table
To eliminate the error message, the cal unit port has to be assigned:
Select the missing port of the cal unit in the "Cal Unit" row.
Close the window with "OK".
Now the calibration can be started with "Take Cal Sweep".