A broadband free-space dielectric properties measurement system at millimeter wavelengths

A free-space measurement system operating in the 75-95 GHz range is used to measure the complex transmission coefficient of a vertical polarized wave through a planar sample for different incidence angles. The complex permittivity is obtained form the measurement data by means of a nonlinear least-squares estimate. The multiple reflections between the transmitting and receiving horn antenna are removed by the time domain gating technique. A dielectric lens collimates the beam of the transmitting horn antenna for minimisation of diffraction effects at the edges of the sample. The performance of the measurement setup has been tested using glass samples. An accuracy of better than 0.04% and 0.5% for the real part and imaginary part of the complex permittivity, respectively, has been achieved.