Hi everyone!
I'm not sure 'cause I never worked with it but I think it must be impossible to stimulate the port with two signals in quadrature in a transient solver simulation since the input signals can't be everlasting sinusoids.
By the way, when you set farfield monitors and simulate your structure, you should find, in the folder containing the farfields results, two files in which the anthenna pattern is reported relatively to the left circular polarized part of the farfield and to the right one respectively.
Is it what you were looking for?