Characterization of Dielectric Substrates Using Dual Band Microwave Sensor

In this work, a compact, inexpensive, and efficient dual band microwave sensor is proposed. The sensor is based on two Complementary Symmetric Split-Ring Resonators (CSSRRs) and possesses a high $Q$ factor and wide sensing range. These CSSRRs are coupled electrically with two inductive patches to the Microstrip Transmission Line (MTL). This combination provides two dual bands, first at 5.35 GHz with a notch depth of -55.20 dB and second at 7.99 GHz with a notch depth of -22.54 dB. The sensor works in transmission mode and senses shift in frequency. Some commonly available dielectric substrates with relative permittivity ranges between 1 and 12 are considered Material Under Test (MUT), and detailed sensitivity analysis is being performed for each band. The dual band sensor is fabricated on a low-cost, widely available FR4 substrate and measured by CEYEAR AV3672D vector network analyzer. Additionally, the least square curve fitting method is used to develop a mathematical model for the measured results. An excellent agreement is observed between simulated, measured, and formulated results.