Comparison of Open-Ended Coax and TDR sensors for the measurement of soil dielectric permittivity in microwave frequencies
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Institute of Agrophysics, Polish Academy of Sciences, Doświadczalna 4, P.O. Box 201, 20-290 Lublin 27, Poland
Int. Agrophys. 2004, 18(4): 355-362
The study presents a comparison of two sensors for the determination of the complex permittivity of soil: a three- rod TDR probe and an Open-Ended Coax probe. The measurements were performed using a TDR system working with a 20 ps rise-time step pulse and a Vector Network Analyzer (VNA) operating in the frequency range from 20 kHz to 8 GHz. The sensors were calibrated on liquids of known dielectrical properties and were used to measure the complex permittivity of three types of soil at various moisture levels. The real part of the complex permittivity calculated from S11 parameters measured by VNA for frequencies near 1 GHz is in agreement with the values measured by TDR method using three-rod probes. The values of the imaginary part of the complex permittivity of the soil samples measured by the probes applied also show a good correlation. The comparison of the hardware differences between the systems for the measurement of the complex permittivity of porous materials working in time and frequency domains is also discussed.
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