Hello I have defined my single waveguide port to have 2 modes for CP antenna exitation.
but CST for some reason made each mode into separate port .
So i have S(1)(2) type of params
although i only have one port.
What is the physical meening of such S-params?
Thanks.
I don't use CST, but in other software the same is also done. It simply means the scattering parameter at port m with respect to mode n. So for example, you have the reflection coefficient (S11,11) as seen by mode 1, but also the reflection coefficient S(12,12) as seen by the second mode at port 1.
The underlying assumption here is that the modes are linearly independent at the port.
They are the modes supported by whatever waveguide you are exciting your network with. In the case of a solid metal waveguide, these would be the various waveguide modes; or in the case of multiple conductors the lowest-order modes would be the multiconductor transmission line modes.