compute the modes(cutoff frequencies) using 2D-FDTD analysis

Can anyone tell me if I can compute the modes(cutoff frequencies) of a circular
waveguide using 2D-FDTD analysis?In my approach no symmetry in the φ direction
is assumed.I use cylindrical coordinates(2D-FDTD analysis in the r-φ plane).

If someone could answer I would appreciate!It's urgent!

dear friend :
I WANT TO STIMULATE THE dielectric slab with 3D FDTD WITH 3D PML BOUNDARY CONDITION ,BUT MY CODE DOESN'T WORK ,CAN YOU SEND MY A CODE ABOUT 3D FDTD WITH 3D PML?I WILL BE APPRICIATED.MY EMAIL IS
shenhongj2008@hotmail.com