Propagation constant using port excitation

Dear All,

I have a question regarding the usage of propagation constant parameter for port excitation in the EM frequency domain simulation.

I tried to use the port functionality to excite an EM wave in a 2d geometry. I used a very simple rectangular geometry with PEC boundary conditions on the sides parallel to the x axis (length). The input excitation port was used on one of the side parallel to the y axis, with the user defined electric field as:
Ex=0, Ey=0, Ez=1.

1) Is the propagation constant defined always in the x direction (normal to excitation side).
2) If I assume that the propagation constant is in the x direction, I expect a phase shift in the Electric field vector for varying value (real) of propagation constant at any point in the x axis. However, I observed a change in magnitude (for emw.normE field) without any expected phase shift. Could you please help me to understand this?

Thanks,
Rahul