Guilin Sun
Ansys Employee

Totally agree with Stefan! The waveguide can support only one fundamental mode, but it does not forbid the dipole to radiate power to other radiation modes. If you have lab experience in lauching fiber modes, you will know that the initial section of the fiber will be bent to get ride of all other non-fundamental modes.

Regarding to Stephan's radial propagation source in a plane, it can only happen if the radiation cancells each other. I think it is difficult, ecept a cylindrical line source, which has the same radial property at each plane in the 3rd dimension, and therefore it is a 2D problem. But if you need to interact with the sources from intermittent simulation result, you may need to do iterated simulations, somehow.