I am trying to get the transmission through a waveguide for the fundamental TE and TM modes. For one of the modes if I sweep the number of modes vis the mode convergence sweep there is a point where the transmission drops for including a particular number of modes and then picks back up with more modes.
Can someone explain the cause of this? It appears the results are more stable for using a smaller number of modes?
Here is the mode convergence sweep (This is the S42 value, and I launch the fundamental TE and TM modes into port one as the sources)
This is the simulation file if helpful
2018_11_03_1550_Bridge_Coupling_BT_4000_WT_800_Swp_BW_WW.lms (355.0 KB)