Improved Angular-Domain Reflection-Only Soil Permittivity Extraction Method Using Spectral Free-Space Measurements

An extraction method is devised for accurate relative permittivity εr of soil samples using angular-domain reflection-only spectral free-space measurements. Different from the angular-domain extraction method which uses an error model considering the return loss function Hi(ω) and the product of transmitting and receiving transfer functions Ht(ω) and Hr(ω), the proposed error model considers not only Hi(ω) and Ht(ω)Hr(ω) but also the feedback loss transfer function Hf (ω). In addition, the proposed method generalizes the normal-incidence extraction method using Ht(ω), Hr(ω), and Hf (ω) to any oblique incidence. An improvement in εr determination by considering the Hf (ω) term in our angular-domain extraction algorithm is shown by a numerical analysis and free-space measurements of two soil samples. It is also validated by measurements that relative errors in εr determination decrease if Hf (ω) term is considered in the extraction procedure. The proposed extraction method was also tested for a combination of different incidence angles and for an inaccurate sample thickness.