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We have studied the frequency dependence of the dielectric constant of YBa2Cu3O7 Josephson junctions fabricated on bicrystalline substrates with different angles tilted around alpha and c axis. The ratio of the dielectric constant to the thickness of the barrier, epsiv/t, can be deduced by measuring the voltage of Fiske steps Veta = etaOslash0c macr/ omega, where eta is the resonance number, omega the junction width and Oslash0 the magnetic flux quantum. Changing a technological parameter as omega we are modifying Veta, so the resonant frequency f n = V eta/Oslash0 for each fixed eta . This makes possible to generate experimentally a dispersion relation of the dielectric constant of the barrier, epsiv(f n) = epsiv(omega) . For all the bicrystalline geometries investigated, data can be fitted to the expression of epsiv(omega) that describes the behavior of the dielectric constant close to a resonance in a dielectric medium with losses. Consistent with the analysis of transport parameters, the values deduced for the resonance frequency and damping constant show a tendency to a more semiconductive behavior with the increase of the misorientation angle. In terms of the equivalent circuit RLC, we can obtain additional information on the inductive response of the barrier.