Parallel Plate waveguide

I am trying to simulate a parallel plate waveguide with HFSS ... I am using the Perfect - E and Perfect - H boundary condition for the side walls ... I used the waveports for the excitation ... however, as I plot the Imag(Gammma), I saw a lot of propagating modes inside the structure before propagation of TE1 or TM1 modes ... I am totally confused about these modes ... Does anybody has some experiences in simulation of Parallel Plate waveguide?

the HFSS tutorial as i remember presents a complete detailed project of simulation of a waveguide and its explanation thereof.

yes sure, but only for rectangular waveguide ...