Measurement of Soil Moisture Using Microwave Sensors Based on BSF coupled lines

This research introduces the conceptualization and examination of a microwave sensor incorporated with a microstrip band stop filter. The microwave sensor's design and assessment are based on microstrip parallel coupled lines, employing a band stop filter configuration at 2.45 GHz on FR4 substrate. The study encompasses the evaluation of soil moisture spanning from 20 to 80%. The measurement procedure involves a network analyzer, specifically the KEYSIGHT model E5063A, operating within the frequency range of 100 kHz to 4.5 GHz. The investigation centers on scrutinizing the frequency response of the insertion loss (S₂₁) across this spectrum. The outcomes of the experimentation unveil notable disparities in frequency shifts. The resultant frequency values, labeled as (f₀-f₁), manifest at 0, 18, 60, 80, 140, and 200 MHz, sequentially. Remarkably, the correlation between the percentage representation of the frequency shift in the transmission coefficient and the frequency itself emerges distinctly, even as the range of tested samples is fine-tuned.