Retrieving Material Permittivity Under Oblique Incidence

Noncontact measurement of complex permittivity at microwave frequencies is significantly important in various areas of scientific research and engineering applications. The noncontact solution based on nonlinear inversions proposed before are usually set up in 2D scenario. While in experiments, it is hard to restrict the wave vector of incident wave in the horizon plane. In this work, we theoretically and numerically investigate the performance of the subspace-based optimization method (SOM) for two-dimensional objects when considering an oblique incidence, of which the wave vector deviates from the horizon plane. Analytical and simulation results showed that the theoretical model can effectively estimate the deviation introduced by oblique incidence.