rectangular waveguide reflectivity

Hi,

Can anyone explain to me how to obtain the reflection coefficient of a rectangular waveguide?

I have been using the FDTD3D program from taflove with neccessary changes, mur's 1st order ABC.

If possible, pls send me a revelant program.

Thanxs a million.

Reflection coefficient is dependent on Length and load/termination.

I do not really understand what you mean. Can you pls elaborate.

What type of source to be used?