A Dielectric Sensor Based on Differential Microstrip Lines Coupled With Multiple Magnetic-LC Resonators

A differential microstrip lines-based microwave microstrip sensor loaded with multiple magnetic-LC (MLC) resonators is proposed in this manuscript. The proposed microstrip sensor is evolved from a traditional microstrip sensor, which has a single resonator unit excited by a single microstrip line. Based on the traditional one, the differential microstrip lines are added, which can improve the level of common-mode (CM) suppression. In the MLC resonator structure, a meander slot is embedded into the resonator to enhance the electrical field intensity. Three MLC resonators are etched on the bottom layer of the substrate, which can produce three transmission zeros (TZs) of differential mode (DM) due to the mutual coupling between these resonators and their own RLC equivalent circuit models. The three TZs can be regarded as three modes, the TZ in low-frequency band is the first odd-mode, the middle frequency TZ is even-mode, and the high-frequency TZ is the second odd-mode. As the resonance strength of the second odd-mode is relatively low; thus, it is ignored and the first odd-mode and even-mode are considered. Odd- and even-modes can be utilized to retrieve the permittivity of material under test (MUT). In the measurement, the error removal model is established to guarantee the experimental accuracy of MUT. The proposed microstrip sensor has average sensitivities of about 5.53% and 4.55% for odd- and even-modes, respectively. The proposed sensor has some superiorities to previous designs in terms of design structure, CM suppression, and multimode detection.