*.step-n.XX.dft

Format

 XX%dft(1,1)      XX%dft(1,2)      ...      XX%dft(1,Ndft)
 XX%dft(2,1)      XX%dft(2,2)      ...      XX%dft(2,Ndft)
     .                .            ...          .                    
     .                .            ...          .                    
     .                .            ...          .                    
 XX%dft(N,1)      XX%dft(N,2)      ...      XX%dft(N,Ndft)        //all are complex numbers.

n : the time-step.
XX : Ex, Ey, Ez, Hx, Hy, or Hz.

N : The number of grid in the simulation.
N_dft : the number of frequency used for discrete fourier transform.