We present in this paper a simulation of a Superconductor-Insulator-Superco
nductor (SIS) sub-harmonic mixer working at a fundamental frequency of 250G
Hz. With a full five-port model, the mixer performances are studied as func
tions of principal parameters including embedding admittances, local oscill
ator (LO) power and voltage bias, and the results are compared with that fr
om a quasi five-port model.