Soil Permittivity Retrieval by Frequency-Domain Noncontact Free-Space Measurements

An improved deembedding technique is devised for accurate relative complex permittivity$\varepsilon _{rs}$determination of granular soil samples poured into a container using time-gated free-space measurements. Unlike other similar methods in the literature, our technique combines the following unique features: 1) it is calibration-independent, meaning that it can reduce calibration errors arising from improper calibration standards; 2) it is free-from precise location of the container involving the sample, thereby providing flexibility in positioning the container anywhere between reference planes; and 3) it determines unique and stable (ripple-free)$\varepsilon _{rs}$thanks to the implementation of time-gating procedure. Free-space measurements were conducted at X-band (8.2–12.4 GHz) of two different soil samples to validate and assess its performance against other frequency-domain or time-domain methods available in the literature. The effects of any relative offset in antennas positions and angle misalignment on$\varepsilon _{rs}$determination by our method are examined.