Free space quasi-optical instrumentation for dielectric measurements of highly scattering materials in millimeter waves

Complex dielectric permittivity of dyed corn meal has been studied over a wide range of frequency, from 70 to 120 GHz. Transmittance and reflectance spectra have been recorded by using a free space quasi-optical millimeter-wave spectrometer, equipped with a high-power backward-wave oscillator as the source of tunable coherent radiation. The complex permittivity of dyed corn meal has been calculated by using analysis of recorded high-precision reflectance and transmittance spectra. The density dependence of complex dielectric permittivity of dyed corn meal has been studied.