The response to a spatially incoherent sources can be obtained from the results of multiple coherent simulations.
Solvers: FDTD, VarFDTD
Simulation with two dipoles
Two dipoles are simultaneously excited in a single simulation. As the FDTD simulation is inherently coherent, the interference pattern of the radiated fields by the two dipoles is clearly visible in both the movie monitor (linear scale) and frequency monitor (log scale).
Two simulations with a single dipole
Here are the results when only the top or the bottom dipole is excited.
Obtaining coherent and incoherent results from single-dipole simulations
If you coherently sum the results from the two simulations using each dipole, you get the same (coherent) result as in the simulation using two dipoles.
If you incoherently sum the results, you can get the following result where the interference pattern is no longer observable.