y_params = s2y(s_params'z0) converts the scattering parameters s_params into the admittance parameters y_params. The s_params input is a complex n-by-n-by-m array, representing m n-port S-parameters. z0 is the reference impedance; its default is 50 ohms. y_params is a complex n-by-n-by-m array, representing m n-port Y-parameters