Microstrip Lines Loaded with Bandstop Resonators for High Resolution Permittivity Sensing

This paper focuses on the design of microwave permittivity sensors based on microstrip lines loaded with shunt connected series LC resonators. The LC resonator is made of a thin inductive trace connected to a capacitive square patch in the ground plane using a via hole. By producing two branches of the same configuration connected to each other using a T junction, differential sensing is achieved enabling robust detections against environmental factors causing measurement errors and miscalibration. The sensor operation principle is analyzed and validated through lumped-element circuit analysis and practical measurements.