Wideband Frequency Domain Method of Soil Dielectric Property Measurements

Abstract

The measuring methods of the complex relative permittivity (CRP) of the sample in the single coaxial cell at frequencies from tens of hertz to several gigahertz are represented. The frequency range is covered by two instruments: by an LCR meter (frequencies up to 5 MHz) and by a vector network analyzer (VNA) (frequencies from 0.3 MHz to several gigahertz). In the high band (0.1-8.5 GHz), the cell is a coaxial line segment filled with the investigated substance. To determine the CRP, the complex transmission coefficient (scattering matrix parameter S <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">12</sub> ) of this cell is measured by using a VNA. For measurements in the middle range (0.3-100 MHz), the cell is included into the break of the central conductor of a coaxial line of a large cross section. The admittance of the cell is determined by measuring the scattering matrix parameter S <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">12</sub> of the coaxial line of the large cross section. At frequencies below 1 MHz, the cell admittance is measured in the usual way by the LCR meter. Thus, CRP measurements of a substance placed in the same cell are carried out in the whole frequency range from 42 Hz to 8.5 GHz. The examples of CRP measurement of soils with different values of the dielectric constants and loss factors are given. It is shown that the CRP measurement error depends on the values of CRP and frequency. The measurement result error of relative dielectric permittivity obtained with the aid of this method is from 0.4% to 2%.