Time and frequency domain modelling of a normally incident plane wave at a periodic structure

Inhalt:
Many microwave devices fall into the general class of spatially periodic structures, such as optical gratings, frequency selective surfaces (FSS), and electromagnetic band gap (EBG) devices. The finite difference time domain (FDTD) method and the finite element frequency domain (FEFD) method have been employed in the modelling of periodic structures. The finite element time domain (FETD) method is also well suited to model the wideband performance of such complex structures. However, very little work has been done using this technique. Here, for the first time, we present FETD results based on an exact Floquet harmonic boundary condition. Only a single unit cell is modelled in the analysis as, for an infinite periodic structure, Floquet’s theorem applies. The validity of our FETD formulation is confirmed by comparing its result with those of the FEFD method. Two numerical models are considered for this purpose: (a) a dielectric slab grating, and (b) a strip grating.