Hi,
What is the tesbench used for characterization of ft of MOSFET?
Ft requires short circuit current gain but how much current should be at the input?
There is AC current at gate and drain in a RF circuit, and
RFIC designers will talk about fT and fmax variously, whichever
seems most pertinent to their circuit.
1/(Rg*Cdg) probably comes close to one or the other.
That's your Miller bandwidth killer. Optional constants
sold separately, two pi to a customer.