Transmission and Reflection of a Three layered Structure

Hi All,

I had designed a three layered structure. Using PORT 1, I excited the EM wave from the top of the ITO(Indium Tin Oxide) and placed second port(PORT 2) at the bottom of Ag(Silver). I had calculated the reflection and transmission of the sample using S-parameters and the program is going well. I had used Fresnel equations model in the model library as my basis for the three layered structure.

But in addition to this I want to calculate the reflection and transmission of the amorphous Silicon layer(which is placed between the ITO and Ag). I had tried to do it with ports but I cant place ports at the first and second boundary as shown in the attached file.

Is their any way to find this(other than by analytical method). Please take a look at the attached figure of my model.

Thanks in advance.

Regards
Binoy