Thank you, FvM. However, my question is a different one: is it possible to introduce a frequency-variable impedance into a lumped port, just as you would do with a N-port network in Ansoft Designer, for instance, where you could use the S matrix of a s2p file among other formats. The thing is: I am to going to plug my design into an antenna whose impedance profile over the band is not constant, as you can expect, and it is not good enough to assign a fixed valued impedance at the end port.