Antenna toolbox convergence problems

Hello,

I am trying to simulate an antenna with discontinuities by using sparameters methods. I have observed that antenna solver can sometimes result in positive s11 values or NaN solution. This is the case even though maximum mesh edge length is lambda/20. Is there a debugging option or what could be the reason of this weird behavior?

Thanks in advance

[Maadhav Akula]

It would be helpful if you can share the antenna upon which you are working on.