Differential techniques are widely used in communication and sensor systems, as these techniques have been shown to improve the performance. This paper shows how differential sensing of permittivity can be conducted in a simple way. For that purpose, a microstrip line loaded with a pair of stepped-impedance resonators is used in two different resonator connections: parallel and cascade. Each resonator is individually perturbed dielectrically so that: 1) when the two individual permittivities are identical, the structure exhibits a single resonance frequency and 2) when the permittivities are different, resonance frequency splitting occurs, giving rise to two resonances (all these resonances are seen in the form of transmission zeroes). The two sensing approaches are successfully validated through electromagnetic simulations and experiments. By virtue of a differential measurement, robustness against changing ambient factors that may produce sensor miscalibration is expected.