Guilin Sun
Ansys Employee

Thank you for detailed description! It seems this is mainly due to PML reflection: when using mesh accuracy 1, it seems ok even though the image is blurred which is understandable. Please try to use more number of PML layers, and also increase FDTD z span as it is much less than one wavelength.

Dipole radiation is very sepcial. In one direction it has strong radiation with 90 deg to PML. This will need very thick PML.

It is not due to dt factor, so please do not change it.