An attractive microwave free-space method is proposed for permittivity extraction of soil samples using calibration-free time-domain measurements. Different than other similar methods in the literature which use the layer-stripping approach in forward direction in the extraction process, its formalism is based on the layer-stripping approach in backward direction, whereby allowing extraction of permittivity from interfacial reflection coefficient only without resorting to any thickness information, especially useful for time-domain analysis of multilayer structures having multiple reflection terms. Effects of angle misalignment, loss, and surface roughness on the extraction performance of the proposed method are analyzed by numerical examples. Permittivity measurements of three low-loss flat solid samples (polypropylene, polyethylene, and polyoxymethylene) were first performed by a free-space setup operating over 1−18 GHz frequency range to validate our methodology and compare its accuracy against other similar methods in the literature. Thereafter, permittivity measurements of two soil samples sieved with similar and different sizes (coarse- and fine-grained soil samples) by the same free-space setup were then considered to access the applicability and performance of our method for electromagnetic property analysis of homogeneous and partially inhomogeneous soil samples.

A free-space microwave method is proposed for accurate dielectric constant εrmeasurement of flat dielectric samples using time-domain measurements. It does not require any reference data (calibration-independent) and thickness information for εrmeasurement. Besides, it uses only two power peaks of reflected signals of one sample with offset metal termination. It is first validated by simulations and numerical analysis. Free-space εrmeasurements of three low-loss dielectric samples (polypropylene, polyethylene, and polyoxymethylene) are then performed for validation of our method. Its accuracy is compared with the accuracies of similar methods in the literature.

A new microwave method is proposed for accurate determination of complex permittivity$\varepsilon _{\textrm {rs}} = \varepsilon _{\textrm {rs}}^{\prime }--j \varepsilon _{\textrm {rs}}^{\prime \prime }$of soil samples inserted over a holder within the Electronic Industries Association (EIA) 1-5/8” coaxial measurement cell. Such a determination could be indirectly correlated with the volumetric moisture content of soil samples by microwave measurements. The method has three main advantages. First, it utilizes a simple calibration procedure involving uncalibrated measurements of an empty cell, the same cell loaded with a soil holder (a dielectric sample), and the same cell with a soil sample over this holder, thus eliminating the need for any formal calibration procedure. Second, it uses one measurement cell for extracting$\varepsilon _{\textrm {rs}}$. Third, it does not require any numerical toolbox for determining$\varepsilon _{\textrm {rs}}$. The method is validated by simulations of a synthesized soil sample and by experiments with a low-loss polyethylene sample. Its accuracy is examined in reference to: 1) two measurement cells with different lengths (length independence); 2) the position of the holder in the cell; and 3) an offset in sample length. Calibration curves (the volumetric moisture content$\theta _{V}$versus$\varepsilon _{\textrm {rs}}^{\prime }$) obtained from fitting measured$\varepsilon _{\textrm {rs}}^{\prime }$by our method to$\theta _{V}$at 2 and 3 GHz are compared with other calibration curves in the literature for the analysis of the performance of the proposed method (PM). It is shown that calibration curves obtained from our method are similar to those obtained from other methods requiring complex calibration procedures.

A new de-embedding line–line method has been proposed for accurate complex relative permittivity ($\varepsilon _{r}$) determination of soil samples loaded into an EIA 1-5/8” coaxial transmission line measurement system. The method has three main features. First, it bypasses the requirement of calibration of this system by using only two identical coaxial lines with different lengths. Second, it does not need any numerical technique for$\varepsilon _{r}$determination. Third, it does not require knowledge of electromagnetic properties and thickness information of the bead used for supporting soil samples. The method is next validated by simulations performed using a full 3-D electromagnetic simulation program (CST Microwave Studio) and by$\varepsilon _{r}$measurement of a polyethylene (PE) material. Finally,$\varepsilon _{r}$values of three air-dried and water-saturated soil samples having 90% or more sand content with different electrical conductivities (ECs) and gathered from different areas of the city Gaziantep in Turkey, were measured.

A free-space time-domain method is proposed to retrieve dielectric constant ($\varepsilon _{r}$), conductivity ($\sigma _{e}$), and thickness ($d$) of metal-backed low-loss dielectric samples using calibration-independent reflected power peak measurements. Its algorithm is validated by numerical calculations and simulations (CST Microwave Studio) using a sine-modulated Gaussian window. A sensitivity analysis is followed to examine its performance considering the dependencies of reflected power peaks with respect to$\varepsilon _{r}$and$\sigma _{e}$. Free-space time-domain measurements have been implemented after transforming frequency-domain measurements into time-domain ones to extract$\varepsilon _{r}$,$\sigma _{e}$, and$d$of polypropylene, polyethylene, and polyoxymethylene samples.

A simple procedure is proposed for the unique permittivity determination of low-loss materials using transmission-only measurements. The procedure utilizes phase measurements at two frequencies corresponding to any extreme values of the transmission properties. We derived a simple relation for the permittivity extraction.