One-Port Vector Network Analyzer Characterization of Soil Dielectric Spectrum

Accurate determination of soil complex-dielectric-permittivity spectrum is important for various applications, especially for the development of soil moisture sensors that can be used, e.g., in agriculture and for environmental monitoring. Wideband measurement of soil dielectric spectrum requires the use of large-diameter coaxial transmission-line cells connected to a vector network analyzer (VNA). We present a new method for soil dielectric-spectrum characterization in the frequency range of 0.05-3 GHz. Our methodology is based on a wideband one-port VNA measurement of a soil sample inserted into a large-diameter coaxial cell. The key part of our approach is the use of a variable load terminating the coaxial cell to extract the scattering parameters of the sample, which are then fed into a dielectric permittivity extraction algorithm. The system provides quick and repeatable measurements without the use of flexible microwave cables. Also, application of a portable one-port VNA significantly lowers the cost of the system in comparison to two-port setups. We verify our methodology based on measurements of reference materials-polytetrafluoroethylene, isopropanol, and ethanol-and then apply it to characterize the soil samples with different moisture content and salinity. Experimental results confirm the validity of our approach.