active s is the reflection coefficient of one port when another port is excited...
for example, a 2 port system ,the total reflect wave at port 1 is S11*V1+S12*V2
the total reflection coefficient is total reflect wave at port 1 over total incident wave at port 1,then reflect coefficient is (S11*V1+S12*V2)/V1,which is the active S(1:1)
因为传统S参数,每次只在一个端口进行激励,其他端口进行完全匹配。但是在HFSS多端口激励中,传统S参数不能用。只能用Active S param,这样可以考虑其他端口向这个端口传输的能量(即其他端口的耦合分量)。假设有K个端口激励。欲求ActiveSmm:
传统S参数和Active S param的关系ActiveSmm = a1/am*Sm1+a2/am*Sm2+a3/am*Sm3+...+am/am*Smm+....+ak/am*Smk.
其中ak为第K个端口入射波。am为第m个端口入射波,smm为传统S参数