This work presents a compact microwave sensor for soil water content (SWC) measurement based on a Complementary Circular Split Ring Resonator (CCSR) as a slot in a rectangular patch antenna. By embedding the resonant element within the patch antenna, the proposed configuration strengthens the interaction between the electromagnetic field and the soil under test, thereby extending the measurement range of SWC. A multi-parameter optimization technique is introduced that combines the analysis of the resonance frequency ( \(f_r\) ), reflection coefficient ( \(S_{11}\) ), and quality factor (Q). In this approach, shifts in \(f_r\) are associated with variations in effective permittivity, while the magnitude of \(S_{11}\) is used to evaluate coupling efficiency and impedance matching. The Q-factor is further extracted to quantify resonance sharpness and stability, improving discrimination among closely spaced moisture levels. The sensor was validated through full-wave simulations and experimental measurements, demonstrating enhanced sensitivity and an extended detection range. The proposed device accurately detects SWC up to 17%, outperforming conventional CSRR-based configurations. The results indicate that the sensor topology, combined with the proposed multi-parameter analysis, provides a robust and reliable platform for SWC sensing. The sensor is well-suited for applications in precision agriculture, environmental monitoring, and other domains that require accurate, wide-range moisture detection.
