Quadrature in->differential out mixer.How determine Gain,

Dear all,

I am design the Quadrature input (Q_In, Q_Ip and Q_Qn, Q_Qp) and Differential output (D_n, D_p) mixer. How could I determine the Gain and NF of it? Do my propose idea correct or not?
(1) Gain simulation
(Differential output (D_n, D_p)) / I_phase or Q_phase differential input
Does this gain correct to reflect the gain of this mixer?

(2) NF simulation
Differential output (D_n, D_p) as a output in the simulation setting. The input in the simulation is set either (Q_In, Q_Ip) or (Q_Qn, Q_Qp). The simulated result is higher 3dB than the real case. Does this simulation setting correct?

Thanks

wccheng