“…For that purpose, additional elements to the sensing lines, e.g., couplers, or dividers/combiners, are required. Concerning differential-mode resonant sensors, the sensing element is typically a pair of transmission lines loaded with a planar resonator, either a metallic or a slot resonator [24], [25], [253], [254], [255], [256], [257], [258], [259], [260], [261], [262], [263], [264]. In these sensors, the canonical output variable is the differential resonance frequency between the pair of resonator-loaded lines.…”