In this paper, a method to characterize complex permittivity of dielectric is presented. The back-scattered signal from a resonant scatterer placed in contact with the dielectric is used to estimate the dielectric properties. The proposed method was tested in simulation and validated in practice using different dielectric samples and different dielectric thicknesses. This method is wireless, non-destructive, with no restriction on the sample thickness and is done using a VNA and an antenna. Discussions on the geometry of the resonator as well as the calibration step is proposed in order to improve the sensing capability of the approach. Monte-Carlo simulation has been performed to define a confidence interval for the values extracted with the proposed approach in the range 1 to 3.5 for permittivity and 0 to 0.2 for tan δ with a SNR of 20dB. For example, a permittivity εr = 3.54 ± 0.06 and tan δ = 0.0024 ± 0.003 has been measured for Rogers RO4003C and εr = 2.31 ± 0.05 and tan δ = 0.004 ± 0.002 for Duroid RT5880 with different thicknesses. It is also shown in simulation that the approach is compatible with materials having loss tangents up to 0.5, and real permittivity up to 10.