The structure of periodic ferrite with thin's modulation which load on periodic ferroelectric studied. The dispersion characteristics was calculated using the modification of finite element method. It is shown, that when ferroelectric load superimposed on the thickest part of the ferrite then changes of permittivity of ferroelectric load influence to band's gap width. It explains the reasons for the choice of such structure for such effect. The mechanism of the change of bandgap's widh for waves propagating in structure was explained.