Add to ORKG4International audienceAdvanced dielectric spectroscopy enables studying of the ferroelectric complex permittivity. Interpretation with the hyperbolic law provides a better fundamental understanding of the material's tunability: bulk contribution, domain wall vibration and displacements may be discerned. Applications, like mobile telecommunication terminals may profit for the design of miniaturized and tunable antennas. As an example, conception and realization of a notch slot antenna with an integrated ferroelectric thin film varactor is presented